section 10.1 10.1 radioactivity...nuclear chemistry 293 radioisotopes of uranium—primarily...

10.1 Radioactivity

Reading StrategyPreviewing Copy the table below. Beforeyou read the section, rewrite the topicheadings as how, why, and what questions. Asyou read, write an answer to each question.

Key ConceptsWhat happens duringnuclear decay?

What are three types ofnuclear radiation?

How does nuclearradiation affect atoms?

What devices can detectnuclear radiation?

Vocabulary◆ radioactivity◆ radioisotope◆ nuclear radiation ◆ alpha particle◆ beta particle◆ gamma ray◆ background

radiation

In 1896, French physicist Antoine Henri Becquerel (1852–1908) wasexperimenting with uranium salts. He hypothesized that the salts,which glow after being exposed to light, produced X-rays while theyglowed. To test his hypothesis, Becquerel performed an experiment.First, he wrapped a photographic plate in paper. Then, he placed someuranium salts on the plate and set it outside in the sunlight, whichcaused the salts to glow. When Becquerel developed the plate, he got afoggy image. At the time, Becquerel thought that X-rays from the saltshad penetrated the paper and fogged the plate.

Like any good scientist, Becquerel wanted to repeat his experiment,but a spell of bad weather forced him to wait. In the meantime, he left a

wrapped photographic plate and uranium salts in a deskdrawer. After several days, Becquerel decided to developthe plate without exposing the uranium to sunlight. Tohis surprise, he got the foggy image shown in Figure 1A.Later, Becquerel determined that the uranium salts hademitted rays that had never been observed before.

Nuclear DecayBecquerel’s experiment marked the discovery ofradioactivity. Radioactivity is the process in which anunstable atomic nucleus emits charged particles andenergy. Any atom containing an unstable nucleus iscalled a radioactive isotope, or radioisotope for short.

Figure 1 Due to rainy weather,Henri Becquerel postponed hisintended experiment withuranium salts. A Without anyexposure to sunlight, the salts stillproduced a foggy image on aphotographic plate. B For hisdiscovery of radioactivity,Becquerel shared the 1903 NobelPrize for Physics with Marie andPierre Curie.

Question

What is nuclear decay?

b. ?

c. ?

e. ?

Alpha, beta, gamma

d. ?

f. ?

a. ?

Answer

292 Chapter 10

A

B

292 Chapter 10

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Objectives10.1.1 Describe the process of

nuclear decay.10.1.2 Classify nuclear radiation as

alpha particles, beta particles,or gamma rays.

10.1.3 Balance nuclear equations.10.1.4 Identify sources of nuclear

radiation, and describe hownuclear radiation affects matter.

10.1.5 Describe methods of detectingnuclear radiation.

Build VocabularyWord-Part Analysis Point out thetwo vocabulary terms that contain the word radiation (nuclear radiation,background radiation). Explain that theword comes from a Latin word meaning“to spread out from a point.”

Reading StrategyStudent answers may include:a. Nuclear decay is the spontaneouschange of one isotope into another. b. What are the types of nuclearradiation? c. What are the effects ofnuclear radiation? d. One effect ofnuclear radiation is the ionization ofmatter. e. How can nuclear radiation be detected? f. Nuclear radiation can be detected by a Geiger counter or film badge.

INSTRUCT

Nuclear Decay

Many students think that gamma rays, X-rays, and visible light are unrelated.Point out that all three are different partsof the continuous electromagneticspectrum. Explain that the photographicplate in Becquerel’s experiment detectedall three kinds of electromagnetic waves.Just as photographic film can detectvisible light, it can detect X-rays andgamma rays emitted during nucleardecay. Students will read about theelectromagnetic spectrum in Chapter 18.Logical

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Reading Focus

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Section 10.1

Print• Laboratory Manual, Investigation 10B• Reading and Study Workbook With Math

Support, Section 10.1 and Math Skill:Nuclear Equations for Alpha Decay

• Math Skills and Problem SolvingWorkbook, Section 10.1

•Transparencies, Chapter Pretest andSection 10.1

Technology• Interactive Textbook, Section 10.1• Presentation Pro CD-ROM, Chapter Pretest

and Section 10.1• Go Online, Planet Diary, Radioactivity

activity

Section Resources

Nuclear Chemistry 293

Radioisotopes of uranium—primarily uranium-238—werethe source of radioactivity in Becquerel’s experiment. (Recallthat the name of an isotope includes its mass number.)Another common radioisotope is carbon-14, which can befound in fossils like the ones shown in Figure 2.

Unlike stable isotopes such as carbon-12 or oxygen-16,radioisotopes spontaneously change into other isotopesover time. When the composition of a radioisotopechanges, the radioisotope is said to undergo nucleardecay. During nuclear decay, atoms of one elementcan change into atoms of a different element altogether.For example, uranium-238 decays into thorium-234, whichis also a radioisotope.

Types of Nuclear RadiationScientists can detect a radioactive substance by measuring the nuclearradiation it gives off. Nuclear radiation is charged particles and energythat are emitted from the nuclei of radioisotopes. Common types ofnuclear radiation include alpha particles, beta particles, and gammarays. Figure 3 shows the properties of these three types of radiation.

Alpha Decay When a uranium-238 sample decays, it emits alphaparticles. An alpha particle is a positively charged particle made up oftwo protons and two neutrons—the same as a helium nucleus. It hasa 2+ charge. The common symbol for an alpha particle is He. Thesubscript is the atomic number (the number of protons). The super-script is the mass number (the sum of the numbers of protons andneutrons). Another symbol for an alpha particle is the Greek letter �.

Alpha decay, which refers to nuclear decay that releases alpha par-ticles, is an example of a nuclear reaction. Like chemical reactions,nuclear reactions can be expressed as equations. The following nuclearequation describes the alpha decay of uranium-238.

U S Th � He

In alpha decay, the product isotope has two fewer protons and twofewer neutrons than the reactant isotope. In the equation above, themass number on the left (238) equals the sum of the mass numbers onthe right (234 + 4). Also, the atomic numberon the left (92) equals the sum of the atomicnumbers on the right (90 + 2). In other words,the equation is balanced.

Alpha particles are the least penetrating typeof nuclear radiation. Most alpha particles travelno more than a few centimeters in air, and canbe stopped by a sheet of paper or by clothing.

42

23490

23892

42

Figure 3 Within a few years ofBecquerel’s discovery ofradioactivity, Ernest Rutherfordclassified three types of nuclearradiation based on his ownstudies of uranium compounds. Comparing and ContrastingHow do alpha particles, betaparticles, and gamma rays differ interms of charge? In terms of mass?

Figure 2 About 26,000 years ago,more than 100 mammoths died ata sinkhole in Hot Springs, SouthDakota. Scientists figured outhow old the remains were bymeasuring amounts of theradioisotope carbon-14 containedin the mammoth bones.

Radiation Type

Alpha particle

Beta particle

Gamma ray

Symbol Charge Mass(amu)

�, He42

0�1�, e

�

2�

1�

0

4

0

Radium-226

Carbon-14

Cobalt-60

Common Source

Characteristics of Nuclear Radiation

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Types of NuclearRadiationBuild Science SkillsInferring Have students look at Figure 3, which shows the particlesemitted in nuclear decay. Explain that a nucleus that emits an alpha particlegives up two protons and two neutrons(a helium nucleus). A nucleus that emitsa beta particle (an electron) gives up aneutron but gains a proton, because aneutron decomposes into a proton andan electron during beta decay. Ask,Which type of radioactive decaycauses the largest change in theatomic number of a nucleus? (Alphadecay, which reduces the atomic numberof the nucleus by two) Logical, Visual

Build Reading LiteracyCompare and Contrast Refer to page 226D in Chapter 8, whichprovides the guidelines for comparingand contrasting.

Ask students to construct a compare/contrast table. Have them skim thesections on alpha decay, beta decay, and gamma decay. Then, ask students to describe similarities and differences of the decay types in their table. Verbal, Visual

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Customize for English Language Learners

Build a Science GlossaryEncourage English language learners to make a science glossary as they read the section.Suggest that they start with the vocabularyterms and then add any other new terms theyencounter. Encourage students to copy thetable in Figure 3 into their glossary, as these

particles are key to understanding the chapter.Model how to divide words into parts such asprefix, root word, and suffix. Posting a list ofsuffixes and prefixes with their meanings in the classroom will help students when theyencounter new words.

Answer to . . .

Figure 3 Alpha particles have acharge of 2�; beta particles have a charge of 1�; gamma rays have nocharge. Alpha particles have a mass of4 amu; beta particles have a mass of

amu; and gamma rays have no mass.

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Radioactivesample

Paper

Aluminum

Concrete

Lead box

Beta Decay When thorium-234 decays, it releases negativelycharged radiation called beta particles. A beta particle is an electronemitted by an unstable nucleus. In nuclear equations, a beta particle iswritten as e or �. Because of its single negative charge, a beta parti-cle is assigned an atomic number of �1. In Chapter 4, you learned thatan electron has very little mass when compared with a proton. For thisreason, a beta particle is assigned a mass number of 0.

How can an atomic nucleus, which has a positive charge, emit anegatively charged particle? During beta decay, a neutron decomposesinto a proton and an electron. The proton stays trapped in the nucleus,while the electron is released. The following equation describes thebeta decay of thorium-234.

Th S Pa � e

In beta decay, the product isotope has one proton more and one neu-tron fewer than the reactant isotope. The mass numbers of the isotopesare equal because the emitted beta particle has essentially no mass.

Due to their smaller mass and faster speed, beta particles are morepenetrating than alpha particles. As Figure 4 illustrates, beta particlespass through paper, but can be stopped by a thin sheet of metal.

Gamma Decay Not all nuclear radiation consists of charged parti-cles. A gamma ray is a penetrating ray of energy emitted by an unstablenucleus. The symbol for a gamma ray is γ. Gamma radiation has no massand no charge. Like X-rays and visible light, gamma rays are energy wavesthat travel through space at the speed of light.

What is a beta particle?

0–1

23491

23490

0�1

Figure 4 Alpha particles (shownin red) are the least penetratingtype of nuclear radiation. Gammarays (shown in green) are themost penetrating. A concrete slabcan block most but not all of thegamma rays released by aradioactive source. Interpreting Diagrams Whichtype of radiation can penetratepaper but is blocked by aluminumfoil?

For: Activity on radiation

Visit: PHSchool.com

Web Code: ccc-1101

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294 Chapter 10

Use VisualsFigure 4 Emphasize that beta andgamma rays will pass through paper andthat gamma rays will also pass througha thin sheet of aluminum. Ask, Whatmaterials would effectively shield aradioactive source that emitted onlybeta particles? (Aluminum or concrete)Why might concrete be insufficientprotection from gamma rays? (Somegamma rays will pass through concrete,and a concrete wall would have to beseveral meters thick to ensure that thegamma rays were effectively blocked.)Visual, Logical

Stopping RadiationPurpose Demonstrate to students thatradiation can be blocked to varyingdegrees by different materials.

Materials medical X-ray image orphotograph of a medical X-ray image

Procedure Show students the medicalX-ray image. Tell students that wherethe X-rays reached the film, it is black,and where the X-rays were completelyblocked, the film is clear. When lightshines through the clear part of the X-ray, it looks white. Ask, Which blocksX-rays better, bone or soft tissue?(Bone, because the white area on theimage means that the X-rays did notreach the film.) How can X-rays tell you about the thickness of bone?(Thick bone is really clear on the film orwhite in the image because it absorbsmost of the X-rays. Thinner bone is lightgray because some X-rays pass throughthe bone.) What do you think a metalobject would look like on an X-rayimage? (It would be white because itwould block the X-rays.)

Expected Outcome Students shouldbe able to relate the penetrating powerof X-rays to the penetrating power ofnuclear radiation. Visual, Verbal

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Section 10.1 (continued)

Find links to additional activitiesand have students monitorphenomena that affect Earth and its residents.

Explaining Energy The amount of energyemitted in alpha and gamma decay is equal tothe energy difference of the nucleus before andafter emission. However, this is not true in betadecay. Physicists had difficulty explaining thisdiscrepancy, because the law of conservation of energy states that the total energy shouldremain unchanged during the process. In 1930,

physicist Wolfgang Pauli proposed that anundetected particle, called the neutrino, was emitted along with the beta particles,accounting for some of the energy change in beta decay. In 1956, the neutrino wasdirectly observed for the first time by Americanphysicists Frederick Reines and Clyde Cowan.

Facts and Figures


Balancing Nuclear EquationsWrite a balanced nuclear equation for the alpha decayof polonium-210.

Read and UnderstandWhat information are you given?

Reactant isotope � polonium-210

Radiation emitted � He (alpha particle)

Use the periodic table to obtain the atomic number ofpolonium.

Reactant isotope � Po

Plan and SolveWhat unknowns are you trying to calculate?

Atomic number of product isotope, Z � ?

Mass number of product isotope, A � ?

Chemical symbol of product isotope, X � ?

What equation contains the given information?

Po S X � He

Write and solve equations for atomic mass andatomic number.

210 � A � 4 84 � Z � 2

210 � 4 � A 84 � 2 � Z

206 � A 82 � Z

According to the periodic table, the element with an atomicnumber of 82 is lead, Pb. So, X is Pb. The balanced nuclearequation is shown below.

Po S Pb + He

Look Back and CheckIs your answer reasonable?

The mass number on the left equals the sum of the massnumbers on the right. The atomic number on the leftequals the sum of the atomic numbers on the right. Theequation is balanced.

42

20682

21084

42

AZ

21084

21084

42

1. Write a balanced nuclearequation for the alpha decayof thorium-232.

2. Write a balanced nuclearequation for the beta decayof carbon-14.

3. Determine the product of alphadecay for americium-241.

4. Determine the product of betadecay for strontium-90.

Solutions1. 232

90Th h AZX � 4

2HeA � 232 � 4 � 228Z � 90 � 2 � 88X � Ra232

90Th h 22888Ra � 4

2He

2. 146C h A

ZX � 0�1e

A � 14 � 0 � 14Z � 6 � (�1) � 7X � N146C h 14

7N � 0�1e

3. 24195Am h A

ZX � 42He

A � 241 � 4 � 237Z � 95 � 2 � 93X � NpAZX � 237

93Np

4. 9038Sr h A

ZX � 0�1e

A � 90 � 0 � 90Z � 38 � (�1) � 39X � YAZX � 90

39Y Logical

For Extra HelpRemind students that when they write and solve the equation for atomicmass and atomic number, they mustremember to change the sign of theconstant when it is moved to the leftside of the equation. Logical

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text foradditional help.

Additional Problems1. Write a balanced nuclear equation forthe alpha decay of uranium-238. (238

92U h 23490Th � 4

2He)

2. Write a balanced nuclear equation forthe beta decay of sodium-24. (2411Na h 24

12Mg � 0�1e)

Logical, Portfolio

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Answer to . . .

A beta particle is anelectron emitted by an

unstable nucleus.

Figure 4 Gamma rays are the mostpenetrating type of nuclear radiationshown in the diagram.

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During gamma decay, the atomic number and mass number of theatom remain the same, but the energy of the nucleus decreases. Gammadecay often accompanies alpha or beta decay. For example, thorium-234emits both beta particles and gamma rays (abbreviated as �) as it decays.

Th S Pa � e � �

Gamma rays are much more penetrating than either alpha particles orbeta particles. It can take several centimeters of lead or several metersof concrete to stop gamma radiation.

Effects of Nuclear RadiationYou may not realize it, but you are exposed to nuclear radiation everyday. Most of this is background radiation, or nuclear radiation thatoccurs naturally in the environment. Radioisotopes in air, water, rocks,plants, and animals all contribute to background radiation. Most rocks,such as the one in Figure 5, contain at least trace amounts of radioac-tive elements. Another source of background radiation is cosmic rays.Cosmic rays are streams of charged particles (mainly protons and alphaparticles) from outer space. Collisions between cosmic rays and Earth’satmosphere shower the surface below with nuclear radiation. All thisradioactivity may sound dangerous. However, background radiationlevels are generally low enough to be safe.

When nuclear radiation exceeds background levels, it can damage thecells and tissues of your body. Nuclear radiation can ionize atoms.When cells are exposed to nuclear radiation, the bonds holdingtogether proteins and DNA molecules may break. As these moleculeschange, the cells may no longer function properly.

Alpha particles, beta particles, and gammarays are all forms of ionizing radiation. Alphaparticles can cause skin damage similar to a burn,but they are not a serious health hazard unless analpha-emitting substance is inhaled or eaten. Forexample, radon gas is a potentially dangerousnatural source of alpha particles because it canbe inhaled. Radon-222 is formed through a seriesof nuclear decays that begins with uranium-238in rocks deep underground. As radon-222 is pro-duced, it seeps upward toward the surface. Itsometimes collects in the basements of buildingsthat lack proper ventilation, as shown in Figure 6.Prolonged exposure to radon-222 can lead tolung cancer.

0–1

23491

23490

Figure 6 Radon gas is producedunderground as the uranium inrocks and soil decays. As theradon seeps up through theground, it can get into buildingsby passing through cracks or holesin their foundations. Inferring How would ventilationof the basement affect radonlevels in the house shown below?

Figure 5 The mineral autunite isan important source of uranium.

Insulation, modern windows,and modern buildingmaterials keep radon fromescaping.

Radon gas dissolvedin water is releasedthrough agitation.

Radon naturally diffuses up through the ground.

Radon is produced by the nuclear decay of uranium found in rocks and soil.

Radon enters through pinholes and cracks in the foundation.

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Effects of Nuclear RadiationUse Community ResourcesArrange to have someone from yourstate or local health department cometo your class to talk about the hazards ofradon. Have students prepare questionsfor the speaker in advance. The speakercan inform students about the possibledangers of radon in their homes andwhat kinds of tests are available. Thespeaker may also provide information onwhat the EPA considers to be safe radonlevels. Have pairs or groups of studentswrite thank-you notes to the speaker,incorporating a few of the facts thatstudents learned from the presentation.Interpersonal, Group

Integrate Earth ScienceRadon is a naturally occurring radio-active element that is formed in thedecay chain of uranium-238. Uraniumcan be found in almost all rocks and soil.Fortunately, in most areas the amount ofuranium in rocks and soil is very small.Higher concentrations of uranium andits minerals are commonly found in light colored igneous rocks, granite,dark shale, phosphate-containingsedimentary rocks, and metamorphicrocks derived from these rocks. Soilsderived from these rocks also have highuranium concentrations. Encouragestudents to work in small groups toresearch the concentrations of uraniumin their community. They may uselibrary resources, such as the Internet, to assist them in their research.Group, Portfolio

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Radon Radon is a colorless, odorless,tasteless gas. The most stable isotope, radon-222, is produced by the alpha decay ofradium-226. The fact that radon may be aserious health hazard was not recognizeduntil the late 1980s. Today, radon isconsidered by some to be the second leadingcause of lung cancer in the United States,after smoking. Cigarette smokers who

become exposed to radon are at particularlyhigh risk of lung cancer.

There are three naturally occurring isotopesof radon. Radon-222 has the longest half-life,3.82 days. Radon-220, with a half-life of 51.5 seconds, is formed in the decay chain of thorium-232. Radon-219, with a half-life of 3.92 seconds, is formed in the decay chainof actinium-227.

Facts and Figures

Answer to . . .

Figure 6 Radon enters buildings fromunderground. Therefore, ventilatingthe basement of the house in Figure 6would help reduce overall radon levels.

Section 10.1 Assessment

Reviewing Concepts

1. How does an element change duringnuclear decay?

2. What are three types of nuclear radiation?

3. How are atoms affected bynuclear radiation?

4. What devices can be used to detectnuclear radiation?

5. How do types of nuclear radiation differ inelectric charge?

6. Describe the penetrating power of eachcommon type of radiation.

7. What is background radiation? List some ofits sources.

Critical Thinking

8. Predicting What is the effect of beta decayon the composition of a nucleus?

9. Inferring Why do you think airplane pilotswear film badges?

10. Write a balanced nuclear equation forthe alpha decay of radium-226.

11. Write a nuclear equation that describesthe beta decay of hydrogen-3.

When exposure to nuclear radiation is external, the amount oftissue damage depends on the penetrating power of the radia-tion. For example, beta particles can damage tissues in thebody more than alpha particles, but less than gamma rays.Gamma rays can penetrate deeply into the human body,potentially exposing all organs to ionization damage.

Detecting Nuclear RadiationAlthough you can’t see, hear, or feel the radioactivityaround you, scientific instruments can measurenuclear radiation. Devices that are used to detectnuclear radiation include Geiger counters and filmbadges. A Geiger counter, shown in Figure 7, uses a gas-filled tube to measure ionizing radiation. When nuclearradiation enters the tube, it ionizes the atoms of the gas.The ions produce an electric current, which can be meas-ured. The greater the amount of nuclear radiation, thegreater the electric current produced in the tube is.

Recall that in Becquerel’s experiment, nuclear radiation left animage on a photographic plate. Today, many people who work with ornear radioactive materials wear film badges to monitor their exposureto nuclear radiation. A film badge contains a piece of photographicfilm wrapped in paper. The film is developed and replaced with a newpiece periodically. The exposure on the film indicates the amount ofradiation exposure for the person wearing the badge.


Figure 7 Wearing protectiveclothing, a firefighter uses aGeiger counter to test the groundfor radioactivity. Firefighterssometimes help clean upaccidents involvingradioactive materials.

Detecting NuclearRadiationUse VisualsFigure 7 Have students carefullyexamine the photograph. Ask, Why is it important to wear protectiveclothing around radioactive materials?(Protective clothing keeps radioactivematerials away from skin.) Tell studentsthat the EPA recommends heavy clothingas protection from beta radiation. Ask,Does a Geiger counter protect againstthe effects of nuclear radiation? (No. The Geiger counter serves only as amonitoring device, not a shielding device.)Visual, Logical

ASSESSEvaluate UnderstandingRandomly ask students to name thesymbol or charge for each type ofnuclear decay.

ReteachUse Figure 4 to summarize the threedifferent types of nuclear decay andhow each type affects matter.

Solutions10. 226

88Ra h AZX � 4

2HeA � 226 � 4 � 222; Z � 88 � 2 � 86;X � Rn; 226

88Ra h 22286Rn � 4

2He

11. 31H h A

ZX � 0�1e

A � 3 � 0 � 3; Z � 1 � (�1) � 2; X � He; 31H h 3

2He � 0�1e

If your class subscribesto the Interactive Textbook, use it toreview key concepts in Section 10.1.

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6. Alpha particles are the least penetrating.Most alpha particles can be stopped by asheet of paper or by clothing. Beta particlespass through paper, but can be stopped bymetal foil. Gamma rays, which are muchmore penetrating than either alpha particlesor beta particles, can pass through severalmeters of concrete.7. Background radiation is nuclear radiationthat occurs naturally in the environment.Sources of background radiation includecosmic rays, and rocks and minerals thatcontain radioactive elements.

8. In beta decay, a neutron decomposes intoa proton and an electron. Therefore, the massnumber stays the same while the atomicnumber (the number of protons) increases by one. The net effect of beta decay is thatthe number of neutrons in the nucleusdecreases by one and the number of protons increases by one.9. Because they work at high altitudes, pilotsare exposed to high levels of backgroundradiation from cosmic rays. To monitor theirradiation exposure, pilots wear film badges.


1. During nuclear decay, atoms of oneelement can change into atoms of another element.2. Three types of nuclear radiation are alphaparticles, beta particles, and gamma rays.3. Nuclear radiation can ionize atoms.4. Geiger counters and film badges are twodevices used to detect nuclear radiation.5. Alpha particles have a charge of 2�; betaparticles have a charge of 1�; gamma rayshave no charge.


10.2 Rates of Nuclear Decay

Reading StrategyIdentifying Details Copy the concept mapbelow. As you read, complete it to identifydetails about radiocarbon dating.

Key ConceptsHow do nuclear decayrates differ from chemicalreaction rates?

How do scientistsdetermine the age of anobject that containscarbon-14?

Vocabulary◆ half-life

A well-known theory is that early Americans were people fromSiberia who crossed the Bering Strait into Alaska about 13,000 yearsago. However, this theory has been challenged by recent scientific dis-coveries. In the 1990s, archaeologists working at a site in Cactus Hill,Virginia, found stone tools, charcoal, and animal bones that were atleast 15,000 years old. Some of the artifacts were as much as 17,000years old. The age of these artifacts suggests that the first Americans

reached the continent much earlier than for-merly thought. Some archaeologists havesince revised their theories on the origin ofAmerica’s earliest ancestors. One possibleexplanation is that the first Americans werepeople from Europe who crossed the AtlanticOcean by using boats.

Figure 8 shows some of the artifactsfrom the Cactus Hill site. They certainly lookvery old, but the archaeologists needed tofind out how old. One clue that can revealthe age of an object is how many radioactivenuclei it contains. Because most materialscontain at least trace amounts of radioiso-topes, scientists can estimate how old theyare based on rates of nuclear decay.

uses the radioisotope can be used to dateobjects as old as

a. ?

Radiocarbondating

b. ? years

Figure 8 These stone tools fromthe archaeological site in CactusHill, Virginia, are at least 15,000years old. Scientists estimated theage of the site based on rates ofnuclear decay.

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Objectives10.2.1 Define half-life, and relate

half-life to the age of aradioactive sample.

10.2.2 Compare and contrast nuclearreaction rates with chemicalreaction rates.

10.2.3 Describe how radioisotopesare used to estimate the age of materials.

Build VocabularyParaphrase Have students write adefinition of half-life in their own words.After students read the section, ask them to draw a diagram that illustratesthe definition.

Reading Strategya. Carbon-14b. 50,000

INSTRUCTBuild Science SkillsDrawing Conclusions Ask students to look at Figure 8. Tell them that if the object is made of an organic (once-living) material, the object’s carbon-14content can be used to determine itsage. Ask, The tools shown in the photoare made of stone. Do you think thestone tools contain carbon-14? (No,stone is not an organic material.)The caption states that the objects are estimated to be 15,000 years old.If the stone tools were not used todetermine this age, then what was?(The people who made the stone tools also made and used other, organic-basedobjects. These objects, perhaps made ofcloth or wood, were used to determine the age.)Logical

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Reading Focus

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Section 10.2

Print• Laboratory Manual, Investigation 10A• Reading and Study Workbook With

Math Support, Section 10.2• Transparencies, Section 10.2

Technology• Interactive Textbook, Section 10.2• Presentation Pro CD-ROM, Section 10.2• Go Online, NSTA SciLinks, Half-Life

Section Resources

Half-lifeA nuclear decay rate describes how fast nuclear changes take place in aradioactive substance. Every radioisotope decays at a specific rate that canbe expressed as a half-life. A half-life is the time required for one half ofa sample of a radioisotope to decay. After one half-life, half of the atomsin a radioactive sample have decayed, while the other half remainunchanged. After two half-lives, half of the remaining half decays, leav-ing one quarter of the original sample unchanged. Figure 9 illustrates thenuclear decay rate of iodine-131. Iodine-131 has a half-life of 8.07 days.After two half-lives, or 16.14 days, the fraction of iodine-131 remainingis one quarter. After three half-lives, or 24.21 days, the fraction of iodine-131 remaining is one half of one quarter, or one eighth.

Half-lives can vary from fractions of a second tobillions of years. Figure 10 lists the half-lives of somecommon radioisotopes. Uranium-238, for instance, hasa half-life of 4.5 billion years. This means that in 4.5 bil-lion years, there will be half as much uranium-238 onEarth as there is today. You could also say that 4.5 billionyears ago, there was twice as much uranium-238 onEarth as there is today. Unlike chemical reactionrates, which vary with the conditions of a reaction,nuclear decay rates are constant. Regardless of thetemperature, pressure, or surface area of a uranium-238sample, its half-life is still 4.5 billion years.

What is a half-life?


100

50

25

12.5

01 half-life 2 half-lives 3 half-lives

Time

Rad

iois

oto

pe

Rem

ain

ing

(%

)Iodine-131

Xenon-131

Nuclear Decay

Isotope

Half-life Nuclear RadiationEmitted

Half-Lives and Radiationof Selected Radioisotopes

3.82 days

8.07 days

24.1 days

1620 years

5730 years

75,200 years

7.04 � 108 years

1.28 � 109 years

4.47 � 109 years

Radon-222

Iodine-131

Thorium-234

Radium-226

Carbon-14

Thorium-230

Uranium-235

Potassium-40

Uranium-238

�

�

�, �

�, �

�

�, �

�, �

�, �

�

Figure 9 The half-life for thebeta decay of iodine-131 is8.07 days. After one half-life(8.07 days), half of a sample ofiodine-131 will have decayed intoxenon-131. After two half-lives(16.14 days), three quarters of thesample will have decayed.

Figure 10 Nuclear decay ratesare constant. A given radioisotopedecays at a specific rate, or half-life. Calculating What isotope isproduced by the nuclear decayof radon-222?

Half-LifeUse VisualsFigure 9 Ask, What happens to theamount of iodine-131 at the end ofthe first half-life? (Half of the iodine-131atoms change into xenon-131 atoms.)Look at the line on the graph. Why isthe line curved and not straight? (Aftereach half-life, half of the remaining atomshave decayed. After one half-life, one halfof the original atoms remain; after twohalf-lives, a fourth of the original atomsremain; and so on. After n half-lives, ( )n

of the original atoms remain. A graph ofthis relationship is a curve, not a straightline.) Visual

Predicting DecayPurpose Students learn that it is notpossible to predict which atom decays in a radioactive sample.

Materials hot plate, 250-mL or 500-mLbeaker, glass plate, popcorn, cooking oil

Procedure Place the beaker on the hotplate. Pour a small amount of cookingoil into the beaker and add popcorn toform a single layer 1 kernel thick. Putthe glass plate on top of the beaker. Tell students that each kernel representsan atom that will decay. Explain to stu-dents that it is not possible to accuratelypredict which kernel will pop first. Tellstudents that when radioisotopes decay,they decay throughout the samplerather than in one particular area.

Safety Caution students to stand at asafe distance when you heat the cookingoil and pop the corn. Remind studentsnever to eat anything in a laboratory.

Expected Outcome There will be no observable pattern to the order inwhich the kernels pop. Visual, Logical

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Customize for for Inclusion Students

Visually ImpairedGive students 75 metal washers. Have thestudents count out 40 washers and line themup in a single row. Explain that after the firsthalf-life of a radioisotope, half of the atomsdecay. Next, have them count out 20 washersand put them in a single row next to the firstrow of washers. Have them repeat this againfor the second half-life with 10 washers, andthen count out 5 washers for the third half-life.

With all the rows even at the left, the studentsshould be able to determine the shape of the“graph” by touching the right edge of eachrow. Inform students that in reality, exactly half of the particles do not decay each half-life, but that this process averages out to the half-life rate over a long period of time. However,reinforce that the general shape of the “graph” is accurate.

Answer to . . .

Figure 10 Polonium-218. Theequation is:22286Rn h 218

84Po � 42He

A half-life is the timerequired for one half of

a sample of a radioisotope to decay.


Modeling Half-Life

Procedure1. Put 100 1-cm squares of wallpaper in a large

plastic bag. Construct a data table with 2columns and 9 blank rows. Label the columnsSpill Number and Number of Squares Returned.

2. Close the bag and shake it to mix up thesquares. Then, spill them onto a flat surface.

3. Remove the squares that are face-side up.Record the number of squares remainingand return them to the bag.

4. Repeat Steps 2 and 3 until there are nosquares left to put back into the bag.

Analyze and Conclude1. Analyzing Data How many spills were

required to remove half of the squares? Toremove three fourths of the squares?

2. Using Graphs Graph your results. Plot spillnumber on the horizontal axis and the numberof squares remaining on the vertical axis.

3. Using Models If each spill represents oneyear, what is the half-life of the squares?

Suppose you have a one-gram sample of iridium-182, which under-goes beta decay to form osmium-182. The half-life of iridium-182 is 15 minutes. After 45 minutes, how much iridium-182 will remain inthe sample? To solve this problem, you first need to calculate how manyhalf-lives will elapse during the total time of decay.

Half-lives elapsed � � � 3

After three half-lives, the amount of iridium-182 has been reduced byhalf three times.

� � �

So after 45 minutes, � 1 gram, or 0.125 gram, of iridium-182remains while 0.875 gram of the sample has decayed into osmium-182.

Radioactive DatingNow suppose you have a sample that was originally iridium-182, butthree quarters of it have since decayed into osmium-182. Based on thefraction of iridium-182 left (one quarter), you can calculate the age ofthe sample to be two half-lives, or 30 minutes old.

The artifacts from Cactus Hill were dated by measuring levels ofcarbon-14, which has a half-life of 5730 years. Carbon-14 is formed inthe upper atmosphere when neutrons produced by cosmic rays col-lide with nitrogen-14 atoms. The radioactive carbon-14 undergoesbeta decay to form nitrogen-14.

C S N � e0–1

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45 min15 min

Total time of decayHalf-life

For: Links on half-life

Visit: www.SciLinks.org

Web Code: ccn-1102

300 Chapter 10

300 Chapter 10

Modeling Half-Life

Objective After completing this activity, studentswill be able to• analyze data to calculate the “half-life”

of a model radioactive element.

Students may think that a half-life is half the time it takes for a radioactivesubstance to decay completely. This labcan help dispel this misconception.

Skills Focus Analyzing Data,Calculating, Using Graphs

Prep Time 20 minutes

Materials 100 1-cm squares of wall-paper, large plastic bag, graph paper

Advance Prep Use a paper cutter tocut up the wallpaper quickly.

Class Time 20 minutes

Teaching Tips• Students can cut up the paper squares

themselves.• Explain to students that, on average,

half the remaining squares will beremoved each time Step 4 is repeated.

• Ask students: How does this labmodel radioactive decay? (Like thewallpaper squares, half the radioactiveelement decays during each half-life.)

Expected Outcome Students will needto spill and remove paper squares six tonine times to remove all of the squares.

Analyze and Conclude1. On average, half the squares will beremoved in one spill and three-fourths ofthe squares will be removed in two spills.2. Students’ graphs should reflect theinformation in their data tables.3. One yearVisual, Logical

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Radiocarbon Dating An American chemist,Dr. Willard F. Libby, developed this technique in the late 1940s. Radiocarbon dating is used to date once-living materials. The date whenthe organism died is the date when it stoppedabsorbing carbon-14.

Radiocarbon dating cannot be used to datethe remains of organisms that died after the1940s. Starting in the 1940s, the testing ofnuclear bombs and use of nuclear reactors hasdramatically increased the amount of carbon-14and other radioisotopes in the environment.

Facts and Figures

Download a worksheet on half-lifefor students to complete, and findadditional teacher support fromNSTA SciLinks.


Reviewing Concepts

1. How are nuclear decay rates different fromchemical reaction rates?

2. How can scientists determine the age ofan object that contains carbon-14?

3. If a radioactive sample has decayed until onlyone eighth of the original sample remainsunchanged, how many half-lives have elapsed?

4. What type of nuclear radiation is emittedwhen carbon-14 decays?

Critical Thinking5. Predicting Can radiocarbon dating be used

to determine the age of dinosaur fossils?Explain. (Hint: Dinosaurs roamed Earth morethan 65 million years ago.)

6. Inferring All of the isotopes of radon havehalf-lives shorter than four days, yet radon isstill found in nature. Explain why all the radonhas not already decayed.

7. Calculating A certain isotope of technetiumhas a half-life of six hours. If it is given to apatient as part of a medical procedure, whatfraction of the radioisotope remains in the bodyafter one day?

Carbon reacts with oxygen in the atmosphere and forms carbondioxide. As plants absorb carbon dioxide during photosynthesis, theymaintain the same ratio of carbon-14 to carbon-12 as in the atmos-phere. Likewise, animals have the same ratio of carbon isotopes as theplants they eat. When a plant or animal dies, however, it can no longerabsorb carbon. From this point on, the organism’s carbon-14 levelsdecrease as the radioactive carbon decays. In radiocarbon dating,the age of an object is determined by comparing the object’s carbon-14 levels with carbon-14 levels in the atmosphere. For example, if theratio of carbon-14 to carbon-12 in a fossil is half the ratio in the atmos-phere, then the organism lived about 5730 years ago.

Because atmospheric carbon-14 levels can change over time, thecalculated age of the fossil is not totally accurate. To get a more accu-rate radiocarbon date, scientists compare the carbon-14 levels in asample to carbon-14 levels in objects of known age. Such objects mightinclude trees (which can be dated by counting tree rings) or artifactsfrom a specific historical period.

Radiocarbon dating can be used to date any carbon-containingobject less than 50,000 years old, such as the artifact in Figure 11.Objects older than 50,000 years contain too little carbon-14 to bemeasurable. To date objects thought to be older than 50,000 years,scientists measure the amounts of radioisotopes with longer half-lives than carbon-14. Geologists, for instance, use the half-lives ofpotassium-40, uranium-235, and uranium-238 to date rock formations.The older the rock, the lower are the levels of the radioisotope present.


Figure 11 Radiocarbon datinghas helped archaeologists learnmore about ancient civilizations.Excavations in Abydos, a majorarchaeological site of ancientEgypt, have unearthed fascinatingartifacts. This mummy case,containing the remains of a cat, is1900 years old.

Explanatory Paragraph Archaeology is thestudy of past cultures. Explain how a conceptin chemistry led to advances in archaeology.


Radioactive DatingBuild Science SkillsMeasuring Ask students to choose a radioactive isotope for dating ahypothetical fossil. Tell students thatarchaeologists hypothesize that the fossilis about 20,000 years old. Have studentslook at the half-lives of radioisotopes inthis section. Ask, Which isotope wouldyou recommend that the scientistsfirst try? (Carbon-14) Why would thatisotope be a good choice? (It is a goodchoice because the half-life of carbon-14 is5370 years. The half-life of radium-226,at 1620 years, is too short. The half-life ofthorium-230 is 75,200 years, which is toolong. Using either of these could result in aless accurate measurement.)Logical, Verbal

ASSESSEvaluate UnderstandingRandomly ask students to determine thenumber of particles present after one,two, or three half-lives have passed froma specified initial number of particles.

ReteachUse Figure 10 to review how differentradioisotopes may be used to dateobjects of different ages. Emphasize thatsome radioisotopes with shorter half-lives are useful for dating young objectswhile radioisotopes with long half-livesare useful for dating old objects.


Half-life is a concept in nuclear chemistrythat has led to profound advances inarchaeology, the study of past cultures. A half-life is the time required for one halfof a sample of a radioisotope to decay.Using radioisotopes such as carbon-14,scientists have been able to accuratelydate fossils and archaeological sites up to 50,000 years old.

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5. Dinosaur fossils, about 65 million years old, are too old to be radiocarbon dated.Radiocarbon dating can only be used to date objects less than 50,000 years old.6. Radon isotopes are still found in naturebecause they are continually formed by thedecay of longer-lived radioisotopes. 7. Assuming the technetium is eliminated onlyby radioactive decay, then Half-Lives elapsed �Total time of decay/Half-Life � 24 hours/6 hours� 4. After four half-lives, the amount has beenreduced by half four times. ( )4 �

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1. Unlike chemical reaction rates, nucleardecay rates are constant.2. The age of an object is determined bycomparing the object’s carbon-14 levels withcarbon-14 levels in the atmosphere.3. Three half-lives ( � � � ) have elapsed.4. When a carbon-14 nucleus decays, it emitsa beta particle.

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302 Chapter 10

Should Radon Testing in Schools Be Mandatory?

Radon Testing in Schools Should Be MandatoryThe EPA estimates that indoor radon exposurecontributes to 21,000 lung cancer deaths in theUnited States each year. After smoking, radon is thesecond-leading cause of lung cancer.

Students and teachers spend extended periodsof time indoors at school. A nationwide survey ofradon levels in schools found that nearly one in fiveschools has at least one classroom with radonexceeding the EPA's action level of 4 pCi/L.

Indoor radon can be easily tested. If elevatedradon levels are found, they can be reduced usingproven techniques. But without mandatory testing,school administrators may not be aware of thepotential risk of radon exposure in their schools.

Radon Testing in Schools Should Not Be MandatoryThe EPA’s radon guidelines are based mainly onstudies of workers in uranium mines. Radon levels inthese mines were far greater than those found inhomes or schools. In addition, the miners engagedin tiring labor, resulting in heavy breathing of thesurrounding air. Lastly, most of the miners weresmokers. The data from these studies areappropriate for predicting the risk of radon exposurefor uranium miners—but not for the general public.

The EPA’s action level of 4 pCi/L is notuniversally accepted. In Canada and Europe, forexample, radon guidelines are much less strict. Untilscientists gather more data about the risk ofresidential radon exposures, radon testing in schoolsshould not be mandatory.

Radon (Rn) is a radioactive element that forms from the nuclear decay ofuranium in rocks and soil. A colorless, odorless gas, radon can enter buildingsthrough drains, cracks in the floors and walls, and even the water supply. Indoorradon levels tend to be highest in places that are close to the soil and have littleventilation, such as basements or crawl spaces.

When a person inhales radon-contaminated air, the lungs trap radioactiveparticles. As these particles decay, radiation is released into the lung tissue. Overtime, repeated exposure to high radon levels can result in lung cancer.

The Environmental Protection Agency (EPA) identifies 4 picocuries per liter(pCi/L) of air as the national “action level” for radon. (A picocurie is a unit ofradioactivity.) If an indoor space has a radon level of 4 pCi/L or higher, the EPArecommends that steps be taken to reduce it. Such steps might include installing aventilation system and sealing cracks in the building's foundation

The Viewpoints

1. Defining the Issue In your own words, explainthe issue that needs to be resolved about indoorradon.

2. Analyzing the Viewpoints List twoarguments of those who think that radon testingshould be mandatory in schools. List twoarguments of those who think that radon testingshould not be mandatory in schools.

3. Forming Your Opinion Should there bemandatory radon testing in schools? Whichargument did you find more convincing?

Research and Decide

For: More on this issueVisit: PHSchool.comWeb Code: cch-1100

302 Chapter 10

Should Radon Testing inSchools Be Mandatory?BackgroundPrior to 1984, radon gas was considereda health risk only for workers in uraniummines. Then, in 1984, a nuclearengineer set off an alarm while passingthrough a radiation monitor at theLimerick Nuclear Power Plant. Theengineer, Stan Watras, was leaving workat the time. Since there was no nuclearfuel on site, there was no major sourceof radiation contamination at the plant.The Health Physics staff at the plantdetermined that the source of theradiation was Mr. Watras’s house inBoyertown, Pennsylvania. The staff tookremedial actions to fix Mr. Watras’home. Mr. Watras and his family still livein the house today.

The Watras case put radon testing in thenational spotlight. In October of 1988,Congress passed legislation thatestablished a national goal that indoorradon levels not exceed ambientoutdoor radon levels (0.2–0.7 pCi/L). Apicocurie (Ci) is a unit of radioactivityequal to 0.037 disintegrations persecond. The law set aside funds forstates to initiate radon testing in schoolsand workplaces.

Answers1. The issue that needs to be resolved iswhether indoor radon poses a health riskserious enough in schools to warrantmandatory testing. 2. Two reasons why radon testingshould be mandatory in all schools isthat radon is the second leading causeof lung cancer in the United States andthat many classrooms are above theEPA’s action level of 4 pCi/L.3. Answers will vary based on whicharguments students choose.

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Have students further researchissues related to this topic.

10.3 Artificial Transmutation

Key ConceptsHow do artificialtransmutations occur?

How are transuraniumelements produced?

Vocabulary◆ transmutation◆ transuranium elements◆ quark

Reading StrategyMonitoring YourUnderstanding Previewthe Key Concepts, topicheadings, vocabulary, andfigures in this section. Listtwo things you expect tolearn. After reading, statewhat you learned abouteach item you listed.

During the Middle Ages, a number of people, like the ones shownin Figure 12, were obsessed with the idea of changing lead into gold.For centuries, these early scientists, known as alchemists, tried to usechemical reactions to make gold. But no matter how many recipesthey tried, the alchemists only succeeded in making compounds thatcontained lead. What were they doing wrong?

Nuclear Reactions in the LaboratoryThe alchemists were trying to achieve transmutation. Transmutation isthe conversion of atoms of one element to atoms of another. It involvesa nuclear change, not a chemical change.

Nuclear decay is an example of a transmutation that occurs natu-rally. Transmutations can also be artificial. Scientists can performartificial transmutations by bombarding atomic nuclei with high-energy particles such as protons, neutrons, or alpha particles.

Early experiments involving artificial transmutation led to impor-tant clues about atomic structure. In 1919, a decade after he discoveredthe atomic nucleus, Ernest Rutherford performed the first artificialtransmutation. Rutherford had been studying the effects of nuclearradiation on various gases. When Rutherford exposed nitrogen gas toalpha particles, he found that some of the alpha particles wereabsorbed by the nitrogen nuclei. Each newly formed nucleus thenejected a proton, leaving behind the isotope oxygen-17.

N � He S O � H

Note that H represents a proton. Rutherford’s experiment providedevidence that the nucleus contains protons.

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What I Expect What I Learnedto Learn

a. ? b. ?

d. ?c. ?

Figure 12 This painting of analchemist’s laboratory was madearound 1570. The alchemistsfailed in their attempts to turnlead into gold.

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FOCUS

Objectives10.3.1 Describe and identify

examples of transmutation.10.3.2 Describe how transuranium

elements are synthesized.10.3.3 Explain how particle

accelerators have been used in scientific research.

Build VocabularyParaphrase Ask students to write thevocabulary words on a sheet of paper.Instruct students to write a definition, intheir own words, for each term as theyencounter the term while going throughthe chapter. After writing their owndefinition, they should also write acomplete sentence with the term.

Reading StrategyPossible answers: a. Examples of artificialtransmutation b. Rutherford’s trans-mutation of nitrogen-14 into oxygen-17; the synthesis of neptunium-239c. Uses of transuranium elementsd. Smoke detectors (americium-241);space probes (plutonium-238)

INSTRUCT

Nuclear Reactions in the Laboratory

The alchemists of the Middle Ages neversucceeded in turning lead into gold. This doesn’t mean, however, that it isimpossible. Modern scientists, includingGlenn Seaborg in 1980, have reportedlyturned lead into gold. However, this has only been done with very minuteamounts of lead. Challenge students tofind out why scientists do not manufac-ture gold for profit using transmutation.(The process of using nuclear reactions tochange lead into gold is more expensivethan the worth of the gold. Currently, it ischeaper to mine gold ore.) Verbal

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Reading Focus

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Print• Reading and Study Workbook With


Technology• Interactive Textbook, Section 10.3• Presentation Pro CD-ROM, Section 10.3

Section Resources

Section 10.3


304 Chapter 10

Transuranium ElementsElements with atomic numbers greater than 92 (uranium) are calledtransuranium elements. All transuranium elements are radioac-tive, and they are generally not found in nature. Scientists cansynthesize a transuranium element by the artificial transmutationof a lighter element.

Neptunium was the first transuranium element synthesized. In1940, scientists at the University of California, Berkeley, bombardeduranium-238 with neutrons, producing uranium-239. The uranium-239underwent beta decay to form neptunium-239.

U S Np � e

Although most transuranium elements have only been producedfor research, some are synthesized for industrial or consumer use. Forexample, americium-241 is a transuranium element used in smokedetectors. As americium-241 decays, it emits alpha radiation. Thisradiation ionizes the air inside a smoke detector to allow an electriccurrent to flow. When smoke enters the smoke detector, it disrupts

the current and the alarm goes off. Another useful transuraniumelement is plutonium-238. Figure 13 shows a space probe that runs

on electrical energy generated by the decay of plutonium-238.

What is a transuranium element?

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Modeling Transmutation

Materialsperiodic table, 2 sheets of unlined white paper,32 green beads, 32 purple beads

Procedure1. Use the periodic table to complete the

following nuclear reaction. Then, write it onone of the sheets of paper.

B � He S X � H

2. Count the number of protons and neutronspresent in each reactant and product.

3. Using the green beads to represent protonsand the purple beads to represent neutrons,

make a model of each reactant and productbelow its symbol on the sheet of paper.

4. Repeat Steps 1 to 3 using the following nuclearreaction and the second sheet of paper.

N � He S X � H

Analyze and Conclude1. Applying Concepts What was the missing

product in each of the equations? How didyou know what the missing product was?

2. Using Models Make a model of the nuclearreaction between an alpha particle and anatom of aluminium-27. (Hint: One of the twoproducts is a proton.)

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Figure 13 In 1977, the NationalAeronautics and Space Adminis-tration (NASA) launched twoidentical spacecraft, Voyager 1 andVoyager 2. These spacecraft,which are still exploring the outersolar system, are powered by thealpha decay of plutonium-238.Inferring What isotope isproduced by the alpha decayof plutonium-238?

304 Chapter 10

TransuraniumElements

Modeling Transmutation

ObjectiveAfter completing this activity, studentswill be able to • balance equations that describe

simple nuclear reactions.

Skills Focus Calculating, Using Models

Prep Time 5 minutes


Safety Caution students to avoiddropping beads on the floor where theymay lead to slips and falls.

Expected Outcome The products arecarbon-13 and oxygen-17.

Analyze and Conclude1. The missing products were carbon-13and oxygen-17. The models shouldshow that the total number of protonsand neutrons on the left side of theequation is the same as on the right.After counting the number of greenbeads (protons) in the missing productisotope, its identity can be determinedby referring to the periodic table. Themass number of the missing productisotope is the sum of its protons and neutrons.2. Use the following equation to checkstudents’ models.2713Al � 4

2He h 3014Si � 1

1H

Visual

Build Reading LiteracyVisualize Refer to page 354D inChapter 12, which provides theguidelines for using visualization.

Have students keep their books closed.Tell them to listen carefully while youread the paragraph about synthesizingneptunium. Ask students to describehow they visualize what happens in thetransmutation. Then, ask students towork in pairs and discuss how theyvisualized the process. Visual

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Customize for Inclusion Students

GiftedChallenge students to find the names ofdifferent types of subatomic particles besidesprotons, neutrons, and electrons. For example,have them research the six types of quarks.(The six quarks are often called up, down,charmed, strange, top, and bottom.) Then, havestudents find out when they were discovered

and what properties are known about them.Have students create a presentation thatexplains the characteristics and discovery ofseveral subatomic particles. (Other subatomicparticle types or categories include leptons,muons, tau particles, neutrinos, bosons,fermions, gluons, mesons, and baryons.)


Reviewing Concepts

1. How do scientists performartificial transmutations?

2. How are transuraniumelements produced?

3. How does artificial transmutation differ fromnuclear decay?

4. Write the equation for the transmutation thatoccurs when an alpha particle combines withan oxygen-16 atom, emitting a proton.

5. Does fermium-257 undergo nucleardecay? Explain.

Critical Thinking6. Predicting Bombarding a lithium-6 atom

with a neutron produces helium-4 andanother particle. What is that particle?

7. Predicting Curium was first synthesized bybombarding a target isotope with alphaparticles, which produced curium-242 and aneutron. What was the target isotope? (Hint:Use the symbol n to represent a neutron.)

8. Inferring Why can’t the transuraniumelements be made by exposing otherelements to naturally occurring alpharadiation?

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Particle AcceleratorsIn Rutherford’s transmutation experiment, the radioactiveelement radium was used as a source of alpha particles.However, sometimes transmutations will not occur unless thebombarding particles are moving at extremely high speeds.In order to perform such transmutations, scientists usedevices called particle accelerators. In a particle accelerator,charged particles can be accelerated to speeds very close to thespeed of light. The fast-moving particles are guided toward atarget, where they collide with atomic nuclei. With the helpof particle accelerators, scientists have produced more than3000 different isotopes.

Scientists also conduct collision experiments in order tostudy nuclear structure. Since the discoveries of the proton,neutron, and electron, more than 200 different subatomicparticles have been detected. According to the current modelof the atom, protons and neutrons are made up of evensmaller particles called quarks. A quark is a subatomic parti-cle theorized to be among the basic units of matter. Bothprotons and neutrons belong to a class of particles that are made up ofthree quarks. Six types of quarks are currently thought to exist. Two ofthese types were discovered at Fermi National Accelerator Laboratory,also known as Fermilab. Figure 14 shows one of the devices used atFermilab to detect subatomic particles.


Summary Write a brief summary of the firstartificial transmutation, performed by ErnestRutherford. (Hint: Your summary shoulddescribe an example of a nuclear reaction.)

Figure 14 This particle detectorrecords subatomic particlesproduced in the Tevatron, themost powerful particleaccelerator in the world. TheTevatron is located at Fermilab inBatavia, Illinois.

Particle AcceleratorsBuild Science SkillsInferring Ask students to read the firstparagraph of Particle Accelerators. Ask,What evidence supports the claim that most transuranium elements canexist only when atoms are bombardedwith particles at very high speeds?(Transuranium elements generally do notoccur in nature, so the conditions underwhich they are formed are not likely to be found in nature. Most transuraniumelements have been produced only underconditions that can be achieved by using a particle accelerator.) Logical

ASSESSEvaluate UnderstandingAsk students to write three completedequations for transmutations. Havestudents take turns giving the reactantsfor the equation while another studentdetermines the product with the correctnumber of protons and neutrons foreach transmutation.

ReteachHave students look at the transmutationequations in the section and ask them toexplain how transmutation differs fromnuclear decay.

Rutherford performed the first artificialtransmutation while studying the effectsof nuclear radiation on gases. After heexposed nitrogen gas to alpha radiation,he observed that some of the alphaparticles were temporarily absorbed bythe nitrogen nuclei. Each newly formednucleus then ejected a proton, leavingbehind oxygen-17. In this transmu-tation, nitrogen-14 was converted into oxygen-17.

If your class subscribes to the Interactive Textbook, use it toreview key concepts in Section 10.3.

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4. 168O � 4

2He h 199F � 1

1H5. Fermium-257, with an atomic number of100, is a transuranium element and thereforeundergoes nuclear decay.6. Hydrogen-37. Plutonium-2398. Because naturally occurring alpha particlesdo not have enough energy to be used in the synthesis of transuranium elements. The synthesis of transuranium elementsrequires high-energy particles.


1. By bombarding atomic nuclei with high-energy particles such as protons, neutrons, oralpha particles2. By the artificial transmutation of lighterelements3. Artificial transmutation is a nonnaturalprocess in which a nucleus is bombarded withhigh-energy particles. Nuclear decay is anatural process in which an unstable nucleusemits charged particles and/or energy.

Answer to . . .

Figure 13 Uranium-234. Theequation is:23894Pu h 234

92U � 42He

An element with anatomic number greater

than 92


Nuclear MedicineExposure to nuclear radiation is often harmful to thehuman body. However, scientists have also found nuclearradiation to be a powerful tool in the field of medicine.

PET scannerPET (positron emissiontomography) scans use

radioactive tracers toexamine parts of the body,

such as the brain. Thepatient receives an injection

of radioactive tracer. Thetracer produces gamma

rays that are detected bythe scanner.

Because radioisotopes are detectable by their radiation, they canbe used as tracers that map out specific locations in the body. Forexample, the radioisotope iodine-131 is absorbed by the thyroidgland in the throat in the same way that iodine-127 is. If iodine-131 is injected into the body, the radiation it emits will show howwell the thyroid gland is functioning.

Radioactive tracers can also be used to pinpoint the locationof cancer cells. Cancer cells multiply rapidly and absorb glucosemuch faster than normal cells. If the glucose molecules are“tagged” with a radioactive tracer, such as flourine-18, thelocation of the cancer cells can be found by tracking areas of highglucose concentration.

Radioisotopes with short half-lives are chosen for medicaluses. These isotopes decay so rapidly that after only a day or two,practically none of the isotope remains.

PET scan of brainThis scan shows the level of activity indifferent areas of the brain. Glucosetagged with flourine-18 is absorbedmore rapidly in areas of high brainactivity and by cancer cells. Here, redshows the greatest activity and bluethe least.

Tagged glucoseis absorbedslowly in theblue areas,indicatingnormal tissue.

Red color showsgreater glucoseabsorption in possiblycancerous areas.

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306 Chapter 10

Nuclear MedicineBackgroundPET (positron emission tomography)scanning can detect subtle changes inthe body’s metabolism and chemicalreactions. The PET scanner detectsradiation produced by a positron-emitting radioisotope injected into thebody. Chemical compounds containingradioisotopes of carbon, nitrogen, oroxygen are commonly used as tracers.

Once the tracer enters the body, ittravels through the bloodstream to thetarget organ. When the tracer reachesthe target organ, the chemical that it isattached to begins taking part in thechemical reactions. Positrons, theantimatter equivalent of electrons, arereleased from the tracer and collide withelectrons. Each collision annihilates apositron and an electron and releasestwo gamma rays. The PET scannerdetects these gamma rays. The data isfed into a computer and a three-dimensional image is produced of theprocesses occurring in the target organ.

PET scans are used to evaluate anumber of different medical conditions.They can be used to detect cancers,determine the extent to which cancer hasspread, and determine the effectivenessof cancer treatment. PET scans can helpdiagnose brain conditions such asepilepsy and Alzheimer’s disease. Theycan also evaluate cardiac conditions such as heart muscle function andcoronary artery disease.

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■ Write a paragraph describing how radioactivetracers are used in medicine. Indicate whatqualities make a particularradioisotope useful as aradioactive tracer in thehuman body.

■ Take a Discovery Channel VideoField Trip by watching“Nuclear Medicine.”

Going Further

Producing an imageThe scanner detects the

gamma rays and producestwo-dimensional images

like slices through thebrain. The scanner’s

computer then constructs athree-dimensional image

based on the scans.

Gamma ray

Positron

Electron

Gamma raysGamma rays are produced when thetracer emits a positron. A positron is aparticle with the mass of an electron buta charge of 1+. The positron is destroyedupon contact with an electron from anearby atom in the body, and emits twogamma rays in opposite directions.

Atom of tracer isotope

Brain

Gamma-ray detectors

Gamma ray


Video Field Trip

Build Science SkillsUsing Models

Purpose Students model the radiation detected by a PET scanner.

Materials 500-mL beaker; sponges;shallow pans; food coloring; 1-cm stripsof thin and thick cardboard, newspaper,and waxed paper; paper towels


Advance Prep Fill the beaker with waterand add several drops of food coloring.For each group, prepare a solution-soakedsponge placed flat in a pan.

Procedure Distribute several differentstrips to students and have them make a pattern on top of the sponge. Tellstudents to leave some areas of thesponge uncovered. Then, have studentsgently press the paper towel on top ofthe sponge for three seconds and removeit, placing the paper towel faceup next tothe sponge. Ask, How does the patternon the paper towel compare to thepattern of squares on the sponge?(They are similar, but not identical. Thewaxed paper and heavy cardboardcompletely blocked the absorption of thesolution. The newspaper did not block theabsorption at all, and the light cardboardpartially blocked the solution.) If the paper towel were a PET scan, whichareas would show the most activity?(The areas that absorbed the most coloredwater.) Which areas would show theleast? (The areas that absorbed the least.)

Expected Outcome Students will gaina better understanding of how PETimages are formed.Logical, Kinesthetic

Going FurtherDoctors can diagnose certain types ofcancer by using radioactive tracers, orradioisotopes that are injected into apatient. The nuclear radiation emittedby the radioactive tracer is detected byimaging equipment such as a PETscanner. For a radioactive tracer to bepractical, it must be readily absorbed bythe organ(s) that doctors wish to study,and it must have a short half-life so as tominimize the patient’s exposure tonuclear radiation.Verbal, Portfolio

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After students have viewed the Video Field Trip, ask them the following questions: What is nuclearmedicine? (The use of small amounts of radioactivematerials that enable a physician to look inside the body and to treat diseases such as some forms of cancer.) What did Marie and Pierre Curiediscover? (Student answers may include: Theydiscovered radium and polonium.) What did

Irene Curie discover? (She discovered artificial radioactivity by determining that aluminum remained radioactive after being bombarded withradioactive particles.) If radioactive substances are used today to treat certain types of cancer,how was it possible for Marie Curie and IreneCurie to develop a form of cancer by workingwith radioactive substances? (When treating certaintypes of cancer, only small dosages of radioactivity areused. However, when Marie and Irene Curie did theirresearch, they were in contact with large amounts ofradioactive substances for prolonged periods of time.)

Video Field Trip

Nuclear Medicine


308 Chapter 10

FOCUS

Objectives10.4.1 Compare and contrast

nuclear forces.10.4.2 Describe the process of

nuclear fission.10.4.3 Explain how nuclear

reactors are used to produce energy.

10.4.4 Describe the process of nuclear fusion.

Build VocabularyWord-Part Analysis Remind studentsthat they can use what they know aboutword parts to figure out the meanings of words. Point out fission and fusion.Tell students that -ion means “the actof” or “the result of an act.” Explain thatfiss- comes from a Latin word meaning“split” and that fus- comes from anotherLatin word meaning “melted.”

Reading Strategy a. Is the splitting of a large nucleus intotwo smaller fragments b. Widely usedas an energy source c. Is the fusing oftwo small nuclei into one larger nucleusd. Still being researched and developedas an alternate energy source

INSTRUCT

Nuclear ForcesUse VisualsFigure 15 Have students carefullyexamine the illustration. Ask, Why arethere no electric forces betweenprotons and neutrons? (Neutrons have no charge.) What force is able toovercome the electrostatic forces ofrepulsion that exist between protonsin a nucleus? (The strong nuclear force)Visual, Logical

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2

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Reading Focus

1

Section 10.4

Print• Reading and Study Workbook With


Technology• Interactive Textbook, Section 10.4• Presentation Pro CD-ROM, Section 10.4• Go Online, NSTA SciLinks, Fission

Section Resources

308 Chapter 10

10.4 Fission and Fusion

Reading StrategyComparing and Contrasting Copy theVenn diagram below. As you read, contrastfission and fusion by listing the ways they differ.

Key ConceptsUnder what conditionsdoes the strong nuclearforce overcome electricforces in the nucleus?

What property of fissionmakes it so useful?

Vocabulary◆ strong nuclear force◆ fission◆ chain reaction◆ critical mass◆ fusion◆ plasma

Alternative energy sources may someday replace fossil fuels such ascoal and oil. One alternative energy source that is widely used today isnuclear energy. Nuclear energy is the energy released by nuclear reactions.

Shortly after the discovery of radioactivity, scientists realized thatatomic nuclei contained vast amounts of energy. By the late 1930s,scientists discovered that transmutations involved more than justthe conversion of one element into another—they also involved theconversion of mass into energy.

Nuclear ForcesWhat holds the nucleus together? Remember that the protons in thenucleus are all positively charged, so they tend to repel one another.Clearly, there must be an attractive force that binds the particles of thenucleus. Otherwise, the protons would simply push one another away.

The strong nuclear force is the attractive force that binds protonsand neutrons together in the nucleus. Because the strong nuclear forcedoes not depend on charge, it acts among protons, among neutrons,and among protons and neutrons. Over very short distances, thestrong nuclear force is much greater than the electric forces amongprotons. For example, at distances as short as the width of a proton,the strong nuclear force is more than 100 times greater than the electricforce that repels protons. However, the strong nuclear force quicklyweakens as protons and neutrons get farther apart. Figure 15 summa-rizes the forces acting on protons and neutrons in the nucleus.

c. ?a. ?

d. ?b. ?

Fission Fusion

releaseslarge

amountsof energy

Neutron

ProtonProton

Neutron

Neutron

ProtonProton

Neutron

Strong Nuclear Forces

Electric Forces

Figure 15 Two kinds of forces actupon particles in the nucleus.Strong nuclear forces, which areattractive, act on protons andneutrons alike. Electric forces inthe nucleus are repulsive, and actonly among protons. Using Models What atomicnucleus is represented above?


The Effect of Size on Nuclear Forces Electric forces inatomic nuclei depend on the number of protons. The greater thenumber of protons in a nucleus, the greater is the electric force thatrepels those protons. So in larger nuclei, the repulsive electric force isstronger than in smaller nuclei.

The effect of size on the strong nuclear force is more complicated.On one hand, the more protons and neutrons there are in a nucleus,the more possibilities there are for strong nuclear force attractions.However, as the size of the nucleus increases, the average distancebetween protons and neutrons increases. Because the strong nuclearforce only acts over short ranges, the possibility of many attractionsis never realized in a large nucleus. As a result, the strong nuclear forcefelt by one proton or neutron in a large nucleus is about the same asin a small nucleus, as shown in Figure 16.

Unstable Nuclei A nucleus becomes unstable, or radioactive, whenthe strong nuclear force can no longer overcome the repulsive electricforces among protons. While the strong nuclear force does not increasewith the size of the nucleus, the electric forces do. There is, therefore, apoint beyond which all elements are radioactive. All nuclei with morethan 83 protons are radioactive.

FissionIn 1938, two German chemists, Otto Hahn and Fritz Strassman, per-formed a series of important transmutation experiments. Bybombarding uranium-235 with high-energy neutrons, Hahn andStrassman hoped to produce more massive elements. Instead, theirexperiments produced isotopes of a smaller element, barium. Unableto explain their data, Hahn and Strassman turned to a colleague forhelp. In 1939, Lise Meitner, shown in Figure 17, and Otto Frisch,another physicist, offered a groundbreaking explanation for the exper-iments. The uranium-235 nuclei had been broken into smallerfragments. Hahn and Strassman had demonstrated nuclear fission.Fission is the splitting of an atomic nucleus into two smaller parts.

Figure 16 The size of a nucleusaffects how strongly it is boundtogether. A In a nucleuscontaining two protons and twoneutrons, the strong nuclearforces easily overcome the electricforce between the protons. B In anucleus containing many protonsand neutrons, the larger numberof electric forces makes thenucleus less stable.

A Nuclear Forces Acting on a Protonof a Small Nucleus

B Nuclear Forces Acting on a Protonof a Large Nucleus

Electricforces

Strong nuclearforces

ElectricforceStrong nuclear

forces

Figure 17Austrian physicistLise Meitner(1878–1968),shown here, andOtto Frisch werethe first scientiststo describenuclear fission.Meitner correctlypredicted thatfission releaseslarge amountsof energy.

FissionBuild Reading LiteracySequence Refer to page 290D in thischapter, which provides guidelines forusing a sequence.

Have students read the text on nuclearfission on pp. 309 and 310. Then, havestudents do the following:1. Ask students to make a sketch similarto Figure 18. Tell students that they canuse circles to represent the nuclei.Students should use larger circles torepresent the uranium nuclei.2. Have students label and describewhat happens as a neutron strikes theuranium-235 nucleus and the steps thatfollow. Start with the neutron as Step 1.Each following step should be num-bered in sequence.3. Students’ sketches should include asmuch detail as they find from the text,Figure 18, and the caption.Visual, Portfolio

Integrate Language ArtsTell students that scientists in severalcountries were instrumental to theunderstanding of nuclear fission. TheEnglish scientist James Chadwickdiscovered the neutron in 1932. In1934, Italian scientists led by EnricoFermi conducted experiments involvingthe slow-neutron bombardment ofuranium. Fermi’s results promptedGerman chemists Otto Hahn and FritzStrassman, and Austrian physicist LiseMeitner, to further investigate theproducts formed when uranium isbombarded with neutrons. Meitner and Otto Frisch built on the results ofthis research and in 1939 described thefission process. Have students write abrief biography of one of the scientistswho contributed to the understandingof nuclear fission. Verbal

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Customize for English Language Learners

Cloze ReadingSelect and copy an appropriate paragraph fromone of the sections, such as the secondparagraph on p. 309. Leave the first and lastsentences intact, since they are usually theintroductory and concluding sentences. For thesentences in the middle, remove key vocabularywords and replace them with a blank. For

example, leave blanks for protons and neutronsin the second sentence of this paragraph, forproton in the third sentence, and for short in the fourth sentence. Have students read theparagraph and fill in the blanks with theappropriate words. You may create a word bankfor students to use when filling in the blanks.

Answer to . . .

Figure 15 A helium nucleus


310 Chapter 10

Figure 18 illustrates the fission of a uranium-235 nucleus. Noticethat one of the products of the reaction is energy. In nuclearfission, tremendous amounts of energy can be produced from verysmall amounts of mass. For example, the nuclear energy released bythe fission of 1 kilogram of uranium-235 is equivalent to the chemi-cal energy produced by burning more than 17,000 kilograms of coal.

Converting Mass Into Energy In the nuclear equationshown in Figure 18, the mass numbers on the left equal the mass num-bers on the right. Yet when the fission of uranium-235 is carried out,about 0.1 percent of the mass of the reactants is lost during the reac-tion. This “lost” mass is converted into energy.

In 1905, more than 30 years before the discovery of fission, physi-cist Albert Einstein had introduced the mass-energy equation. Itdescribes how mass and energy are related.

Mass–Energy EquationE � mc2

In the mass-energy equation, E represents energy, m represents mass,and c represents the speed of light (3.0 � 108 m/s). The conversion ofa small amount of mass releases an enormous amount of energy.Likewise, a large amount of energy can be converted into a smallamount of mass. The explosion of the first atomic bomb in 1945 offereda powerful demonstration of the mass-energy equation. The bomb con-tained 5 kilograms of plutonium-239. Fission of the plutoniumproduced an explosion that was equivalent to 18,600 tons of TNT.

Recall how the law of conservation of mass applied to chemicalreactions. In nuclear reactions, however, the energies involved are muchlarger. To account for the conversion of mass into energy, a modifiedconservation law is used. According to the law of conservation of massand energy, the total amount of mass and energy remains constant.

Figure 18 The fission ofuranium-235 yields smaller nuclei,neutrons, and energy. The nuclearequation for this reaction can be written as follows.

U� n SKr� Ba�3 n�energy

Comparing and ContrastingHow does fission differ fromnuclear decay?

10

14256

9136

10

23592

For: Links on fission

Visit: www.SciLinks.org

Web Code: ccn-1104

Neutron

Uranium-235U235

92Uranium-236

(very unstable)

U23692

Barium-142Ba142

56

Kr9136

Krypton-91

Energy

310 Chapter 10

Use VisualsFigures 18 and 19 Ask students tolook at both figures. Ask, Why do youthink the uranium-236 atom ismissing in Figure 19? (Uranium-236 isvery unstable and does not last longbefore it splits into two smaller nuclei.)What happens to the amount ofenergy released during a chainreaction? (The amount of energy releasedincreases as the chain reaction proceeds.)Visual

Build Math SkillsFormulas and Equations Askstudents to examine the mass-energy equation anddetermine the units of measurementthat E is equivalent to. Remind themthat the SI units for mass and speed are,respectively, kg and m/s. (Units of E areequivalent to kg � (m/s)2.) Also askstudents to determine what the formulawould be for calculating c. (c � )Logical

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text foradditional help.

$E/m

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Download a worksheet on fissionfor students to complete, and findadditional teacher support fromNSTA SciLinks.

U23592 U235

92

U23592

U23592

U23592

U23592

U23592

U23592

n10

n10

n10

n10

n10

n10

n10

n10

Ba14256

Kr9136

Kr9336

Sr9438

Ba14056

Rb9037

Cs14455

Sn13250

Mo10142

Xe14054

Triggering a Chain Reaction How fast does arumor spread? Imagine that you started a rumor by telling itto three of your friends. Then suppose each of those friends toldthree more friends. If this pattern continued, the rumor wouldquickly spread to hundreds of people, even though it originallystarted with just one person, you.

Nuclear fission can follow a similar pattern, in which one reactionleads to a series of others. During the fission of uranium-235, eachreactant nucleus splits into two smaller nuclei and releases two or threeneutrons. If one of these neutrons is absorbed by another uranium-235nucleus, another fission can result, releasing more neutrons, as shownin Figure 19. In a chain reaction, neutrons released during the splittingof an initial nucleus trigger a series of nuclear fissions.

The speed of a chain reaction can vary. In an uncontrolled chainreaction, all of the released neutrons are free to cause other fissions,resulting in a fast, intense release of energy. Nuclear weapons aredesigned to produce uncontrolled chain reactions. In a controlledchain reaction, some of the neutrons are absorbed by nonfissionablematerials, resulting in only one new fission for each splitting of anatom. The heat from controlled chain reactions can be used to gener-ate electrical energy. Unfortunately, another product of controlledchain reactions is radioactive waste, shown in Figure 20.

In order to sustain a chain reaction, eachnucleus that is split must produce, on average, oneneutron that causes the fission of another nucleus.This condition corresponds to a specific mass offissionable material, known as a critical mass. Acritical mass is the smallest possible mass of a fis-sionable material that can sustain a chain reaction.

What is a chain reaction?

Figure 19 The fission of one nucleuscan trigger a chain reaction. Thesplitting of a uranium-235 nucleus by aneutron yields two or three neutrons,each of which can cause another fission.Interpreting Diagrams Does thefission of uranium-235 always yield thesame isotopes as products? Explain.

Figure 20 A cranelowers drums ofradioactive waste into a landfill inHanford, Washington.


Nuclear ProcessesPurpose Students observe a model ofnuclear fission and fusion.

Materials bubble solution, 2 bubblewands

Procedure Dip the end of each wandinto the solution and remove. Gentlyblow into the ring of each wand tomake a bubble with a diameter a littlelarger than the ring, and catch thebubble on the wand. Bring the wandsand the bubbles together. Press thebubbles together to form one largebubble, illustrating fusion. Pull the twoframes farther apart to separate thebubble into two bubbles, one in eachframe, simulating fission. When this isdone a little faster small bubbles may bereleased, representing the releasedneutron. Discuss with students thestrengths and weaknesses of this model.

Expected Outcome Students observehow to use bubbles to model nuclearfusion and nuclear fission. Students maypoint out that this demonstration doesnot model the neutron required toinitiate fission.Visual, Group

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Natural Nuclear Reactor In 1972 whenFrancis Perrin uncovered evidence of a“natural nuclear reactor” in mines in Gabon,Africa, other scientists questioned his findings.They wanted to know how a natural nuclearreactor could exist when it required preciseengineering work to construct one.

Further study showed that the expectedproportions of uranium-238 (99.3%) anduranium-235 (0.7%), were not present in the

Gabon mines. There was much less uranium-235. Scientists used this data and calculatedthat 1.7 billion years ago, the proportion ofuranium-235 was 3%, enough for nuclearfission. Underground water helped create theright conditions for a chain reaction. Scientiststhink the natural nuclear reaction continuedintermittently for at least a million years untilthe uranium-235 was mostly used up.

Facts and Figures

Answer to . . .

Figure 18 Unlike nuclear decay,fission is generally not spontaneous. A neutron must be introduced in orderfor the fission of uranium-235 to occur.During the nuclear decay of uranium-235, however, no other reactants arenecessary in order for the radioisotopeto decay into thorium-231 and emitalpha radiation.

Figure 19 No. Fission of uranium-235 can produce a number of differentcombinations of product isotopes.Although fission results in the fragmen-tation of the nucleus into two parts,the composition of those two parts(and hence the number of neutronsreleased) can vary widely.

A chain reaction is anuclear reaction

sequence in which neutrons releasedduring the splitting of an initial nucleustrigger a series of nuclear fissions.

312 Chapter 10

Nuclear Energy from Fission Today, nuclear power plantsgenerate about 20 percent of the electricity in the United States. In anuclear power plant, controlled fission of uranium-235 occurs in avessel called a fission reactor.

Unlike power plants that burn fossil fuels, nuclear power plants donot emit air pollutants such as oxides of sulfur and nitrogen. However,nuclear power plants have their own safety and environmental issues.For example, workers in nuclear power plants need to wear protectiveclothing to reduce their exposure to nuclear radiation. In addition, thefission of uranium-235 produces many radioactive isotopes with half-lives of hundreds or thousands of years. This radioactive waste must be

1896 Frenchscientist AntoineHenri Becquereldiscoversradioactivity inuranium.

1932 Firstatom smasher(subatomicparticleaccelerator) isused by JohnCockcroft andErnest Walton.

Nuclear Chemistry Over the last 100 years scientistshave uncovered many secretsabout the atomic nucleus.Developments have rangedfrom the synthesis of newelements to the harnessing ofnuclear power as a viableenergy source.

1890 1910 1930

1905 AlbertEinstein’s mass-energy equation,E = mc2, providesthe basis fornuclear power.

HENRIBECQUEREL

MARIE AND PIERRE CURIE AT WORK IN THEIR LABORATORY

1938Germans OttoHahn and FritzStrassmannproduce nuclearfission bybombardinguranium-235atoms withneutrons.

EQUIPMENT USEDBY HAHN ANDSTRASSMANN

1898 Marie and PierreCurie discover theradioactive elementsradium and polonium. Bymaking radium availableto other scientists, theCuries helped advancethe study of radioactivity.

312 Chapter 10

Nuclear ChemistryEnrico Fermi and his research groupachieved the first controlled nuclearchain reaction while the United Stateswas fighting World War II. This was thefirst nuclear reactor. While this reactorwas used for research, the main purposeof the reactor was to make plutoniumfor the atom bomb. After World War II,the U.S. population rose, and thegrowing population increased thedemand for electricity. Scientists saw thepotential of nuclear energy to help meetthis demand. In 1951, electricity wasproduced using atomic power for thefirst time at a reactor in Idaho. Thereactor produced enough electricity to light four light bulbs. Today, morethan 400 nuclear power plants operateworldwide, with over 100 operating inthe United States.

Have students research nuclear powerplant safety and write a one-paragraphopinion about whether the benefits ofnuclear power generation are worth the risks. Verbal, Portfolio

Possible answer: A number ofgroundbreaking scientific discoverieswithin the last 100 years have set thestage for nuclear energy. In 1905 (lessthan ten years after the discovery ofradioactivity), Albert Einstein introducedhis mass-energy equation, whichdescribed how very small amounts ofmass could be converted into enormousamounts of energy. In 1938, Otto Hahnand Fritz Strassman performed the firstnuclear fission (of uranium). A self-sustaining nuclear chain reaction wasachieved just four years later. By 1951,scientists had developed nuclear fissioninto a promising source of electricalenergy.Verbal

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isolated and stored so that it cannot harm people or contaminate theenvironment while it decays.

Another concern about nuclear power is that the operators of theplant could lose control of the reactor. For instance, if the reactor’scooling system failed, then a meltdown might occur. During a melt-down, the core of the reactor melts and radioactive material may bereleased. If the structure that houses the reactor is not secure, then theenvironment can become contaminated. In 1986, one of the reactorsat the nuclear power station in Chernobyl, Ukraine, overheated duringan experiment. A partial meltdown resulted, and large amounts ofradioactive material were released into the atmosphere.

1942 The firstcontrolled, self-sustainingnuclear chainreaction isachieved byEnrico Fermi’sresearch groupin Chicago.

1950 1970 1990

1945 UnitedStatesexplodes firstatom bomb ina test nearAlamagordo,New Mexico.

ATOM BOMB TEST

1960 Willard Libby winsthe Nobel Prize fordeveloping carbon-14dating. The techniquebecame widely used inarchaeology and geology.

1986Partialmeltdownoccurs atChernobylpower plant.

IDAHO TESTING STATION

ENRICO FERMI

1951 Electricityfrom nuclearfission producedat NationalReactor TestingStation, Idaho.

Summary Write a paragraphabout the history of nuclearenergy based on some of theevents in the time line below.(Hint: Before you write, use aflowchart to organize theevents you wish to include.)

Use Community ResourcesAsk students to find out whatpercentage of the power in their statecomes from nuclear power plants.Encourage them to use library resources,such as the Internet, to find statistics. If your state does not receive powerfrom nuclear power plants, instructstudents to find that information foranother state. Ask students to make adiagram and write a brief summary of their findings. Interpersonal, Portfolio

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314 Chapter 10

Nuclear Power StationSince the first nuclear bomb was exploded in 1945,scientists have found ways of utilizing the enormouspower of nuclear fission for peaceful purposes. Nuclearpower is now a major means of producing electricity.About 20 percent of electricity in the United States isgenerated this way. Interpreting DiagramsHow is water used in a nuclear power station? Fission control

The fission reaction within thereactor core is controlled byneutron-absorbing control rods.Because they are stillradioactive, the used rods areremoved from the reactor coreand stored in a pool, as shownabove.

Waterpressurizer

Reactor coreFission reactions

take place in thereactor core, releasinglarge amounts of heat.

Steam generatorHeat released in the

reactor core is absorbedby water in the steamgenerator. This transfer ofenergy produces largeamounts of high-pressuresteam.

Turbines and condenserThe high-pressure steam forces

the turbine to rotate at great speed.As it cools, the steam condenses toform liquid water, which is thenpiped back to the steam generator.

Condenser

High-pressureturbine

High-strengthprotective shielding

Controlrods

Pump

Water

Steam condenses.

Coolingwaterexits. Cooling

water enters. Filter

Pump

Fuel rods containinguranium dioxide

Electric generatorHere the work done by

the force turning the turbinesproduces electrical energy.

314 Chapter 10

Nuclear Power StationBackground Uranium-235, the fissionable materialused in nuclear power plants, makes uponly about 0.7% of all uranium found innature. In order for a nuclear reactor tooperate, about 3% of the uranium in thefuel rods must be uranium-235. Samplesof uranium must be enriched so thatthey contain this higher percentage ofuranium-235.

A bundle of fuel rods contains slightlymore than the critical mass of uranium-235. Control rods are placed in thebundle in order to control when andhow quickly the process of fission occurs.

Interpreting Diagrams In a nuclearpower station, water is used to transferthe energy generated in the reactor core.Heat released in the core is absorbed bywater in the steam generator. The steamproduced is used to drive a turbine; the kinetic energy of the turbine is thenconverted into electrical energy. Water is also used as a coolant to condense thesteam exiting the turbine. The steamcondenses into liquid water and is pipedback to the steam generator.Visual

For EnrichmentThe U.S. Navy uses nuclear reactors topower many different types of ships,ranging from submarines to aircraftcarriers. Nuclear power is useful on shipsthat are at sea for long periods of timebecause the ships do not have to carrylarge quantities of fuel or refuel whilethey are on a mission. Ask students to research how nuclear reactors in ships differ from those in nuclear power stations. Verbal

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Reviewing Concepts1. Under what conditions does the strong

nuclear force overcome the repulsive effect ofelectric forces in the nucleus?

2. What property of fission makes it auseful reaction?

3. What particles are affected by strongnuclear forces?

4. What must happen in order for a nuclearchain reaction to occur?

5. Why is a cooling system necessary in anuclear reactor?

6. How do the products of a fusion reactiondiffer from the products of a fission reaction?

Critical Thinking7. Inferring How does the strong nuclear force

affect an atom’s electrons? (Hint: Think aboutwhere the electrons are located in the atom.)

8. Inferring Why do fission chain reactions ofuranium-235 not occur in undergrounduranium deposits?

FusionAnother type of nuclear reaction that can release huge amountsof energy is fusion. Fusion is a process in which the nuclei oftwo atoms combine to form a larger nucleus. As in fission,during fusion a small fraction of the reactant mass is con-verted into energy.

On any day or night, you can detect the energy releasedby fusion reactions occurring far away from Earth. The sunand other stars are powered by the fusion of hydrogen intohelium. Inside the sun, an estimated 600 million tons ofhydrogen undergo fusion each second. About 4 million tonsof this matter is converted into energy.

Fusion requires extremely high temperatures. Within the sun,temperatures can reach 10,000,000°C. At temperatures this high,matter exists as plasma. Plasma is a state of matter in which atomshave been stripped of their electrons. You can think of plasma as a gascontaining two kinds of particles—nuclei and electrons.

Fusion may someday provide an efficient and clean source of elec-tricity. Scientists envision fusion reactors fueled by two hydrogenisotopes, deuterium (hydrogen-2) and tritium (hydrogen-3). The fusionof deuterium and tritium produces helium, neutrons, and energy.

H � HS He � n � energy

Scientists face two main problems in designing a fusion reactor. Theyneed to achieve the high temperatures required to start the reaction,and they must contain the plasma.

10

42

31

21


Figure 21 The Tokamak FusionTest Reactor at the PrincetonPlasma Physics Laboratory inPrinceton, New Jersey, was one ofthe very few fusion reactors thathave been built. It was retired in1997 after 15 years ofexperimentation.

Fossil Fuels Reread the description of fos-sil fuels in Section 9.1. Then compare fossilfuel combustion with nuclear fission.

Fusion

Students may think that the sun isactually burning because it gives offlight and heat. Explain that the light andheat given off by the sun result fromnuclear fusion, not combustion.Verbal

Build Science SkillsObserving Tell students that the sunproduces energy by nuclear fusion.Explain that fusion releases very largeamounts of energy. Ask, How do youknow that the sun produces largeamounts of energy? (Students maycome up with examples such as heat,bright sunlight, sunburn, and so on.)Logical

ASSESSEvaluate UnderstandingHave students write down threecharacteristics of nuclear fission andfusion. Have students take turns giving a characteristic while the other studentsidentify whether it is typical of fission or fusion.

ReteachUse Figures 18 and 19 to summarizecontrolled and uncontrolled fissionreactions.

Possible answer: Both fossil fuelcombustion and nuclear fission produceheat, which can be used to generateelectricity. Fossil fuel combustion is achemical reaction, the products ofwhich include carbon dioxide, water,carbon monoxide, nitrogen oxides, andsoot. Air pollution is one of the maindrawbacks of fossil fuel combustion asan energy source. Fission is a nuclearreaction whose products include lighternuclei and neutrons. Radioactive wasteis one of the main drawbacks of fissionas an energy source.


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5. A cooling system is necessary in a nuclearreactor to prevent the reactor core fromoverheating.6. The products of fusion are less massivenuclei such as helium. The products of fissionare more massive nuclei, such as barium or krypton.7. The strong nuclear force has no effect on anatom’s electrons because it acts only over veryshort distances within the nucleus.8. Natural deposits of uranium-235 generallydo not occur in amounts great enough toreach a critical mass.


1. Over very short distances, strong nuclearforces are much greater than the electricforces in the nucleus.2. Tremendous amounts of energy can beproduced from very small amounts of mass.3. Strong nuclear forces act among protons,among neutrons, and among protons andneutrons.4. Each nucleus that splits must on averageproduce at least one neutron that results inthe fission of another nucleus.


290 Chapter 10

Nuclear ChemistryC H A P T E R

This false-color image from a bubble chamber �shows the tracks of subatomic particles at high speed.

How do science concepts apply to yourworld? Here are some questions you’ll beable to answer after you read this chapter.

■ Why is radon gas dangerous? (Section 10.1)

■ How can you measure the age of a rock? (Section 10.2)

■ How does a smoke detector work? (Section 10.3)

■ How can doctors diagnose certain types of cancer? (page 306)

■ How does a nuclear reactor generate electricity? (Section 10.4)

290 Chapter 10

ASSESS PRIORKNOWLEDGEUse the Chapter Pretest below to assessstudents’ prior knowledge. As needed,review these Science Concepts andMath Skills with students.

Review Science ConceptsSection 10.1 Encourage students torecall what they have learned aboutbalancing chemical equations. Reviewhow chemical equations showconservation of mass.

Section 10.2 Encourage students toremember what they have learnedabout the rates of chemical reactions. To prepare students for a discussion ofhalf-life, ask students to recall basicprobability calculations.

Section 10.3 Review the differentparts of the periodic table. Encouragestudents to recall the location ofuranium and the elements heavier than uranium in the periodic table.

Section 10.4 Ask students to recallwhat they have learned about modernmodels of the atom.

Review Math SkillsEquations and Formulas Studentswill need to manipulate variables andconstants to solve for unknowns inequations representing nuclear decay.

Direct students to the Math Skills in the Skills and Reference Handbookat the end of the student text.

CHEMISTRY

Chapter 10

Chapter Pretest

1. According to the law of conservation of mass, if element X has a molar mass of 3 g/mol, and element Y has a molar mass of 5 g/mol, what must be the total mass ofproducts formed when one mole of thecompound X2Y decomposes? (11 g)2. True or False: A reaction rate is the rate at which reactants change into productsover time. (True)

3. If you tossed 128 coins in the air, abouthow many could you expect to land headsup? (b)

a. About 178 b. About 64c. About 32 d. Almost none

4. Suppose you were to remove any coinsthat landed heads up, and then toss theremaining coins in the air. How many timescould you expect to repeat this process

until you had removed all of the coins?(About 7 times)5. The element uranium belongs to (d)

a. Group 7A (halogens).b. Group 8A (noble gases).c. the lanthanide series.d. the actinide series.

6. Which subatomic particles are found inthe nucleus? (Protons and neutrons)

CHEMISTRY

10.1 Radioactivity




Chapter Preview


What Happens When an Atom Decays?Procedure1. Using green beads to represent protons and

purple beads to represent neutrons, make amodel of a nucleus of a beryllium atom thatcontains 4 protons and 4 neutrons.

2. Atomic nuclei such as the one you modeledcan decay by losing a particle that contains2 protons and 2 neutrons. Remove theappropriate number of beads from yourmodel to represent this process.

Think About It1. Observing How many protons and how

many neutrons are left in your nuclear model?

2. Using Models What element does yournuclear model now represent?

Video Field Trip

Nuclear MedicineWhat Happens When an Atom Decays?Purpose In this activity, students beginto describe one mechanism of atomicdecay that causes atoms to change fromone element to another.

Students may think that elements areunchangeable, and they may doubt thatan atom of one element can change toanother. Challenge this misconceptionby asking students to discuss theoutcome of this activity. This activitydemonstrates how elements canchange, though it does not prove thatsuch changes actually occur.

Skills Focus Using Models

Prep Time 5 minutes

Materials green and purple beads


Expected Outcome The model willdemonstrate the decay of 84Be to 42He byloss of an alpha particle (two protonsand two neutrons).

Think About It1. Two protons and two neutrons areleft in the model.2. The model represents helium.Kinesthetic, Logical

L2


Encourage students to view the Video Field Trip“Nuclear Medicine.”

ENGAGE/EXPLORE

Video Field Trip

Nuclear Medicine


316 Chapter 10

In a nuclear fission chain reaction, a nucleus is struckby a neutron, which causes the nucleus to split intotwo smaller nuclei and to release other neutrons. Ifthese neutrons strike other nuclei, a chain reactioncan occur. In this lab, you will model a nuclear fissionchain reaction using dominoes.

Problem How can you make a model of anuclear fission chain reaction?

Materials

Skills Observing, Using Models

Procedure1. Stand 15 dominoes in a single straight row in

such a way that the distance between them isabout one half of their height. Knock over thefirst domino. Measure and record the time ittakes for all the dominoes to fall.

2. Repeat Step 1 two more times. Then, averagethe three time measurements to get a moreaccurate time.

3. Arrange 15 dominoes as shown below so thateach domino will knock over two others.Observe what happens when you knock overthe first domino. Measure and record howlong it takes for the whole set of dominoes tofall over.

• 20 dominoes• watch with a second hand, or stopwatch• metric ruler

Modeling a Chain Reaction4. Repeat Step 3 two more times. Average the

three time measurements to get a moreaccurate time.

5. Set up 15 dominoes again as you did inStep 3. This time, however, hold a metricruler on end, in the middle of the arrangementof dominoes, as shown in the photograph onthe next page. Knock over the first domino.Observe what happens.

6. Set up 15 dominoes as you did in Step 3, butthis time, place 5 additional dominoes behindand at right angles to 5 randomly chosendominoes for support, as shown below. The5 supported dominoes represent atoms of adifferent isotope that must be struck withmore energy to undergo fission.

7. Knock over the first domino. Measure andrecord the time it takes for the dominoes tofall and how many dominoes fall.

8. Repeat Steps 6 and 7 two more times. Then,average the three time measurements to get amore accurate time.

9. Repeat Steps 6 through 8, but this time,place supporting dominoes behind only3 dominoes.

10. Repeat Steps 6 through 8, but this time, placea supporting domino behind only 1 domino.

Modeling a Chain ReactionObjectiveAfter completing this activity, studentswill be able to• describe how a nuclear chain reaction

occurs • list some of the factors that affect the

rate of nuclear chain reactions.

Skills Focus Observing, UsingModels

Prep Time 5 minutes


Teaching Tips• If students have difficulty arranging the

dominoes correctly, perform this lab asa demonstration or provide diagramsof the positions of the bases of thedominoes. Students can then place thedominoes directly on the diagram.

Expected Outcome Rearranging thedominoes from a single line to a fan shapein Steps 3 and 4 increased the speed withwhich they fell. Inserting a metric ruler inStep 5 and adding supporting dominoesin Step 6 prevented some of thedominoes from falling.

L2

316 Chapter 10


6. Inferring What factors do you thinkwould affect the rate of a nuclear fissionchain reaction?

7. Drawing Conclusions What do you thinkwould happen to a nuclear fission chainreaction if control rods were not present?

8. Evaluating and Revising What are some ofthe limitations of using falling dominoes tomodel a nuclear fission chain reaction? Suggesthow you might revise this model to make itmore representative of a chain reaction.

Visit the library and find outabout the Manhattan Project

and how it made history. Use what you havelearned from the falling-dominoes model to helpyou understand the scientific discoveries related tocontrolled and uncontrolled nuclear chain reactions.

Go Further

Analyze and Conclude1. Calculating What was the average fall time

for the arrangement of dominoes in Steps 1and 2? In Steps 3 and 4?

2. Applying Concepts What type of reactionwas modeled in Steps 3 and 4?

3. Using Models In your falling-dominoesmodel of nuclear fission chain reactions, whatdid a standing domino represent? What didthe fall of a domino represent?

4. Using Models In your falling-dominoesmodel of nuclear fission chain reactions, whatdid the striking of one domino by anotherrepresent? What did the metric rulerrepresent?

5. Analyzing Data Before a sample of an easilyfissionable isotope is used, it is refined byremoving less fissionable isotopes of the sameelement. On the basis of your observations inSteps 6 through 10, explain why thisrefinement is necessary.

Analyze and Conclude1. The time should be shorter in Steps 3and 4. 2. A nuclear chain reaction was modeledin Steps 3 and 4.3. A standing domino represented thenucleus of an atom. The fall of a dominorepresented the fission of the nucleusand the release of neutrons.4. The striking of one domino byanother represented the striking of anucleus of a nearby atom by a neutron.The ruler represented a control rod.5. Atoms of the less-easily fissionableisotopes can interfere with thedevelopment of a chain reaction.6. The number of neutrons releasedduring fission and the number of otheratoms that are nearby and available forthe released neutrons to strike affect therate of the reaction.7. The reaction would go out of control,perhaps leading to a meltdown orexplosion.8. One limitation of the domino model is that it treats each fission reaction as the same; according to the model, eachfission reaction (represented by a singlefalling domino) leads to exactly twomore fissions. In reality, the fission ofone nucleus can produce more thantwo neutrons, each of which may trig-ger another fission reaction. One waythat the model could be revised is touse dominoes of varying sizes and/orcolors. The arrangement of dominoescould be modified so that the falling ofa larger-sized domino caused more thantwo smaller-sized dominos to fall.Alternatively, different colored domin-oes could be used to represent thediffering numbers of neutrons releasedby each fission reaction (as well as thedifferent product isotopes formed). Visual, Logical

Go Further

Initiated by the U.S. government duringWorld War II, the Manhattan Project was a large-scale research project thatsucceeded in developing the first atomicbomb. In their research, students mayrelate their knowledge of fission chainreactions to Enrico Fermi’s experimentswith the first nuclear reactor at theUniversity of Chicago in 1942, as well as earlier breakthroughs in nuclearchemistry made by Lise Meitner andFritz Strassman.Verbal



290A Chapter 10

Planning Guide

SECTION OBJECTIVES STANDARDS ACTIVITIES and LABSNATIONAL STATE

A-1, A-2, B-1,B-3

A-1, A-2, B-1,B-6, E-2, F-1,F-5, G-1, G-2,G-3

A-1, A-2, B-1,E-2, F-1, F-2,F-4, F-5, G-1,G-2, G-3

A-1, B-1, B-6,D-1, F-1, F-5,G-1, G-2, G-3

10.2 Rates of Nuclear Decay, pp. 298–301

1 block or 2 periods

10.2.1 Define half-life, and relate half-life to theage of a radioactive sample.

10.2.2 Compare and contrast nuclear reactionrates with chemical reaction rates.

10.2.3 Describe how radioisotopes are used toestimate the age of materials.

10.3 Artificial Transmutation, pp. 303–305


10.3.1 Describe and identify examples of transmutation.

10.3.2 Describe how transuranium elements are synthesized.

10.3.3 Explain how particle accelerators havebeen used in scientific research.

10.4 Fission and Fusion, pp. 308–315


10.4.1 Compare and contrast nuclear forces.

10.4.2 Describe the process of nuclear fission.

10.4.3 Explain how nuclear reactors are used toproduce energy.

10.4.4 Describe the process of nuclear fusion.

10.1 Radioactivity, pp. 292–297


10.1.1 Describe the process of nuclear decay.

10.1.2 Classify nuclear radiation as alphaparticles, beta particles, or gamma rays.

10.1.3 Balance nuclear equations.

10.1.4 Identify sources of nuclear radiation,and describe how nuclear radiationaffects matter.

10.1.5 Describe methods of detecting nuclear radiation.

SE Quick Lab: Modeling Half-Life,p. 300

TE Teacher Demo: Predicting Decay,p. 299

LM Investigation 10A: Modeling Radioactive Decay L2

L2

L2

SE Quick Lab: Modeling Transmutation,p. 304 L2

SE Exploration Lab: Modeling a ChainReaction, pp. 316–317

TE Teacher Demo: Nuclear Processes,p. 311 L2

L2

SE Inquiry Activity: What Happens When an Atom Decays? p. 291

TE Teacher Demo: Stopping Radiation,p. 294

LM Investigation 10B: Detecting Radiation L1

L2

L2

Easy Planner Teacher Express

Nuclear Chemistry 290B

Quantities for each group

STUDENT EDITION

Inquiry Activity, p. 291green and purple beads

Quick Lab, p. 300100 1-cm squares of wallpaper,large plastic bag, graph paper

Quick Lab, p. 304periodic table, 2 sheets ofunlined white paper, 32 greenbeads, 32 purple beads

Exploration Lab, pp. 316–31720 dominoes, watch with asecond hand (or stopwatch),metric ruler

TEACHER’S EDITION

Teacher Demo, p. 294medical X-ray image orphotograph of a medical X-ray image

Teacher Demo, p. 299hot plate, 250-mL or 500-mLbeaker, glass plate, popcorn,cooking oil

Build Science Skills, p. 307500-mL beaker; sponges;shallow pans; food coloring; 1-cm strips of thin and thickcardboard, newspaper, andwaxed paper; paper towels

Teacher Demo, p. 311bubble solution, 2 bubble wands

Materials for Activities and Labs

Chapter Assessment

CHAPTER ASSESSMENT

SE Chapter Assessment, pp. 319–320

CUT Chapter 10 Test A, BCTB Chapter 10iT Chapter 10PHSchool.com GOWeb Code: cca-1100

STANDARDIZED TEST PREP

SE Chapter 10, p. 321TP Diagnose and Prescribe

Go online for these Internet resources.

Web Code: cca-1100Web Code: cch-1102

Web Code: ccc-1101

Web Code: ccn-1102Web Code: ccn-1104

Interactive Textbook withassessment at PHSchool.com

Ability Levels Components

For students who need additional help

For all students

For students who need to be challengedL3

L2

L1 SE Student EditionTE Teacher’s EditionLM Laboratory ManualPLM Probeware Lab

Manual

RSW Reading & StudyWorkbook

MSPS Math Skills &Problem SolvingWorkbook

CUT Chapter & Unit TestsCTB Computer Test BankTP Test Prep ResourcesDC Discovery Channel

Videotapes & DVDs

T TransparenciesiT Interactive TextbookP Presentation Pro

CD-ROMGO Internet Resources

RSW Section 10.1

RSW Math Skill

MSPS Section 10.1

T Chapter 10 Pretest

Section 10.1

P Chapter 10 Pretest

Section 10.1

GO Radioactivity

activity L2

L2

L2

L2

L2

L2

L2

L1 SE Section 10.1Assessment, p. 297

iT Section 10.1

RSW Section 10.2

T Section 10.2

P Section 10.2

GO Half-Life L2

L2

L2


iT Section 10.2

RSW Section 10.3

DC Nuclear Medicine

T Section 10.3

P Section 10.3 L2

L2

L2


iT Section 10.3

RSW Section 10.4

T Section 10.4

P Section 10.4

GO Fission L2

L2

L2


iT Section 10.4

RESOURCES SECTION

PRINT and TECHNOLOGY ASSESSMENT

290C Chapter 10

Chemistry Refresher

Nuclear Radiation 10.1

Radioactivity is the process inwhich an unstable atomicnucleus emits radiation in theform of particles and energy.The release of charged parti-cles from a nucleus results inthe formation of a differentisotope with a different atomicnumber and/or atomic mass.Unlike stable isotopes, radio-isotopes spontaneously decayinto other isotopes.

Three common types ofnuclear radiation are alphaparticles, beta particles, andgamma rays. Nuclear radiationcan ionize atoms. When cellsof living tissue are exposed tonuclear radiation, they may no longer function properly.Nuclear radiation can be monitored using devices such as Geigercounters and film badges.

Half-Life and Radiocarbon Dating 10.2

The rate at which radioisotopes undergo nuclear decay is con-stant for each isotope under all conditions and depends on thenumber (fraction) of nuclei present. The amount of timerequired for half the atoms of a sample of a radioisotope to decayis called the half-life of the radioisotope.

Because the nuclear decay rate for a given radioisotope is con-stant, it can be used to measure the passage of time. Carbon-14is a radioisotope commonly used for this purpose, through amethod called radiocarbon dating. The small fraction of carbonatoms in the atmosphere that are carbon-14 has remainedroughly constant for thousands of years. The carbon-14 is produced by the interaction of cosmic rays from outer space withEarth’s atmosphere. All living organisms take in carbon, a certainpercentage of which is carbon-14. When an organism dies, it nolonger takes in carbon-14. The amount of carbon-14 in the deadorganism decreases over time as the radioactive carbon under-goes beta decay to form nitrogen-14. Scientists can measure theratio of carbon-14 to carbon-12 in the remains of the organism,and use this ratio to estimate how long ago the organism died.

Before you teach

Students may mistakenlythink that gamma rays, X-rays, and visible lightare unrelated. However,they are all part of acontinuous magneticspectrum, and for thatreason, all three affect aphotographic plate in thesame way. For a strategyto overcome this miscon-ception, see AddressMisconceptions onpage 292.

Big IdeasIn the chapters leading to this one, students have focusedon chemical changes. They have learned how electronsmove around in these changes, as ionic or covalent bondsare broken or formed. In nuclear chemistry, students willstudy processes that take place when the nuclei of atomsare affected. Unlike the processes of earlier chapters, thenumbers of neutrons and protons will change, and atomsof one element become atoms of another.

Space and Time Spontaneous nuclear decay proces-ses follow first order kinetics. As a consequence, nucleardecays have a well-defined and constant half-life. Oneapplication of nuclear decay is to determine the ages ofobjects. Carbon-14 is incorporated into all living things,so carbon-14 dating is one method used for dating.Carbon-14 has a half-life of 5730 years. Radioisotopeswith longer half-lives can be used to determine the age of rocks.

Matter and Change Students will first study thedecay processes of a radioactive substance. Three typesof nuclear radiation may be emitted: alpha particles,beta particles, or gamma rays. The first two types areassociated with the change of an atom into an atom of another element or into a different isotope of thesame element. Students will then study fission andfusion processes.

Forces and Motion Electrostatic forces, theattractions between particles of opposite charge andrepulsions between particles of similar charge, havealready been introduced. A student might wonder why a nucleus remains intact, given that it consists ofpositively charged protons and uncharged neutrons.Strong nuclear forces, which act over very shortdifferences, keep these particles together.

Energy Compared to the physical and chemicalchanges that students have already studied, nuclearchanges involve tremendous amounts of energy. Duringprocesses such as fusion, the products have less mass thanthe reactants, and large amounts of energy are released.

From the AuthorDavid FrankFerris State University

Artificial Transmutation 10.3

During nuclear decay, atoms of one element change into atoms ofanother element. This change is called transmutation. Scientistscarry out artificial transmutations by bombarding atomic nucleiwith high-energy particles. This process can be used to synthe-size transuranium elements (elements with atomic numbersgreater than 92), which are not usually found in nature.

Nuclear Forces and Reactions 10.4

The subatomic particles in thenucleus are held together bystrong nuclear forces. Repulsiveelectric forces between protonsexist. In small nuclei, the strongnuclear forces are generallymuch greater than the electricforces. In very large nuclei,however, the opposing nuclearforces become similar instrength, resulting in an unstable nucleus.

A large, unstable nucleusmay undergo nuclear fission,in which it splits into twosmaller nuclei. Fission releases

neutrons and a considerable amount of energy. In the presenceof many unstable nuclei, fission can lead to a chain reaction,which can be either uncontrolled or controlled. An atomic bombexplosion is an example of an uncontrolled chain reaction.A controlled chain reaction occurs in the reactor of a nuclearpower plant.

Another type of nuclear reaction is called fusion, in which twonuclei combine to form one larger nucleus. Fusion reactionsrelease a tremendous amount of energy. The sun is powered bya fusion reaction in which hydrogen nuclei are fused together toform helium nuclei.

Build Reading Literacy

Sequence

Ordering EventsStrategy Help students understand and visualize the steps in aprocess, or the order in which events occur. Sequences frequentlyinvolve cause-effect relationships. Readers can construct graphicorganizers to help themselves visualize and comprehend asequence. For most sequences, flowcharts are the graphic ofchoice. However, cycle diagrams are more appropriate for cycles.Before students begin, locate a description in the text of a several-step process or a chain of causes and effects, such as those inSection 10.4 related to a fission chain reaction (p. 311) or nuclearpower generation (p. 314).

Example1. Have students read the passage, thinking about what takesplace first, second, third, and so on. Point out that the text willnot always use order words such as first, next, then, and finally.2. Review the passage, listing the steps or events in order.3. If the passage describes a chain of steps or events, draw aflowchart on the board, having students tell the sequence ofevents, steps, or causes and effects, and writing each part of theprocess in a separate box.

4. If the passage describes a cycle, use a cycle diagram to showthe sequence.

5. Have students locate additional examples of sequentialrelationships in the text or visuals of the chapter. Students can depict the steps or events using graphic organizers.

See p. 309 for a script on how to use the sequence strategywith students. For additional Build Reading Literacystrategies, see pp. 293 and 304.

Students may incorrectlythink that the sun isburning because the sungives off heat and light. Infact, the light and heatfrom the sun are a resultof nuclear reactions. For astrategy to overcome thismisconception, seeAddress Misconceptionson page 315.

Neutron

Uranium-235U235

92Uranium-236(very unstable)

U23692

Barium-142Ba142

56

Kr9136

Krypton-91

Energy

Nuclear Chemistry 290D

For: Teaching methods for nuclear chemistryVisit: www.SciLinks.org/PDLinksWeb Code: ccn-1099

318 Chapter 10

CHAPTER

10 Study Guide10.1 Radioactivity

Key Concepts

• During nuclear decay, atoms of one elementcan change into atoms of a differentelement altogether.

• Common types of nuclear radiation include alphaparticles, beta particles, and gamma rays.

• Nuclear radiation can ionize atoms.

• Devices that are used to detect nuclear radiationinclude Geiger counters and film badges.

Vocabulary

radioactivity, p. 292; radioisotope, p. 292;nuclear radiation, p. 293; alpha particle, p. 293;beta particle, p. 294; gamma ray, p. 294;background radiation, p. 296


Key Concepts

• Unlike chemical reaction rates, which vary with theconditions of a reaction, nuclear decay ratesare constant.

• In radiocarbon dating, the age of an object isdetermined by comparing the object’s carbon-14levels with carbon-14 levels in the atmosphere.

Vocabulary

half-life, p. 299


Key Concepts

• Scientists can perform artificial transmutations bybombarding atomic nuclei with high-energyparticles such as protons, neutrons, oralpha particles.

• Scientists can synthesize a transuranium elementby the artificial transmutation of a lighter element.

Vocabulary

transmutation, p. 303; transuranium elements, p. 304;quark, p. 305


Key Concepts

• Over very short distances, the strong nuclear force is much greater than the electric forcesamong protons.

• In nuclear fission, tremendous amounts of energycan be produced from very small amounts of mass.

Vocabulary

strong nuclear force, p. 308; fission, p. 309;chain reaction, p. 311; critical mass, p. 311;fusion, p. 315; plasma, p. 315

Concept Map Use information from the chapter tocomplete the concept map below.

Thinking Visually

a. ?

b. ?

Reactions

can beclassified as

including

which canproduce

chemicalreactions

fission nucleardecay

alphaparticles

c. ? d. ?

318 Chapter 10

Study Guide

Study TipOrganize New InformationTell students that learning detail-orientedinformation is easier when using strategiessuch as making outlines of a section,making charts of details, making graphicorganizers, and making flashcards. Tellstudents that by using these techniquesand reviewing them daily, they can avoid“cramming” for a test.

Thinking Visuallya. Nuclear reactionsb. Fusionc. Beta particlesd. Gamma rays

Assessment

If your class subscribes tothe Interactive Textbook, your studentscan go online to access an interactiveversion of the Student Edition and aself-test.

Reviewing Content1. b 2. d 3. c4. d 5. d 6. d7. b 8. a 9. b

10. a

Chapter 10

Print• Chapter and Unit Tests, Chapter 10

Test A and Test B• Test Prep Resources, Chapter 10

Technology• Computer Test Bank, Chapter Test 10• Interactive Textbook, Chapter 10• Go Online, PHSchool.com, Chapter 10

Chapter Resources

Nuclear Chemisty 319

CHAPTER

10 Assessment

Choose the letter that best answers the questions orcompletes the statement.

1. An alpha particle is identical to a. a neutron. b. a helium nucleus. c. an electron. d. a hydrogen nucleus.

2. When a beta particle is emitted, themass number of a nucleus

a. increases by one. b. decreases by one.c. decreases by four. d. remains the same.

3. The most penetrating form of nuclear radiation is a. an alpha particle. b. a beta particle.c. a gamma ray. d. an electron.

4. The half-life of cobalt-60 is 5.3 years. Whatfraction of a sample remains after 21.2 years?

a. one half b. one quarterc. one eighth d. one sixteenth

5. Which of the following is a radioisotopecommonly used in dating archeological artifacts?

a. nitrogen-14 b. carbon-12c. uranium-235 d. carbon-14

6. Transmutation does not occur in which of thesenuclear processes?

a. nuclear fission b. nuclear fusionc. alpha decay d. gamma decay

7. Based on its location on the periodic table, anelement that is not naturally occurring is

a. terbium (Tb). b. curium (Cm). c. holmium (Ho). d. lutetium (Lu).

8. Nuclear particles are held together bya. the strong nuclear force.b. electrical attraction.c. quarks.d. electrical repulsion.

9. Nuclear power plants generate electricity froma. nuclear fusion. b. nuclear fission. c. combustion. d. radioactivity.

10. The primary reaction inside stars changesa. hydrogen to helium. b. helium to hydrogen.c. uranium to plutonium.d. nitrogen to carbon.

Reviewing Content

11. How do radioisotopes of an element differ fromother isotopes?

12. What is the effect on the mass number and chargeof a nucleus when it loses an alpha particle?

13. How do the mass number and charge of anucleus change when it emits a gamma ray?

14. Which type of radiation—alpha, beta, or gamma—is most dangerous to living things? Explain.

15. Why does a Geiger counter occasionally clickeven if no artificial radioisotopes are nearby?

16. How does raising the temperature affect the rateof nuclear decay?

17. Why can’t carbon-14 be used to determine theage of fossils that are several hundred thousandyears old?

18. Write the equation for the transmutation thatoccurs when an alpha particle combines with anitrogen-14 atom, emitting a proton.

19. Compare and contrast the processes of fissionand fusion.

20. What is necessary to sustain a nuclearchain reaction?

21. Why do nuclear reactions produce more energyper mass of matter than chemical reactions?

22. The diagram below shows a nuclear reactor,including control rods. What is the function of acontrol rod in a nuclear power plant?

Understanding Concepts

Interactive Textbook withassessment at PHSchool.com

Controlrods

Fuelrods

Reactor

Coolant

Assessment (continued)

Understanding Concepts11. Unlike stable isotopes, radioisotopesdecay spontaneously by emittingnuclear radiation.12. The mass number decreases by four;the charge decreases by two.13. The mass number and charge areunchanged.14. Gamma rays are more dangerousthan alpha particles or beta particlesbecause they can penetrate deep insidethe body. However, if alpha particles areinhaled or ingested, they can also bedangerous.15. The Geiger counter is detectingbackground radiation.16. Temperature has no effect on ratesof nuclear decay.17. The amount of carbon-14 remainingafter 50,000 years is too low to be easilymeasured.18. 14

7N � 42He h 17

8O � 11H

19. Fission and fusion are both nuclearreactions that convert small amounts ofmatter into large amounts of energy. Infission, a large nucleus is split into twosmaller fragments. In fusion, two lightnuclei are fused into a larger nucleus.Unlike nuclear fission, which is usedwidely as a source of electrical energy,nuclear fusion has yet to be developedinto a reliable alternate energy source.20. In order to sustain a nuclear chainreaction, each fission reaction must on average produce a neutron thatsubsequently causes another fission.21. During nuclear reactions, a smallamount of matter is converted into alarge amount of energy. Duringchemical reactions, matter is notconverted into energy.22. Control rods regulate the nuclearchain reaction by absorbing neutronsproduced by fission reactions that takeplace in the reactor.


Homework GuideSection

10.110.210.310.4

Questions1–3, 11–17, 24–26, 31, 334–5, 27–306–7, 18, 238–10, 19–22, 32

PPLS


320 Chapter 10

CHAPTER

10 Assessment (continued)

Use the figure below to answer Questions 23 and 24.

23. Classifying In the illustrated uranium-238decay sequence, classify the type of radiationreleased in each of the transmutations fromuranium-238 to radon-222.

24. Making Generalizations Study the sequenceof decay from radon-222 to lead-206. Make ageneralization as to what type of decay lead,polonium, and bismuth undergo until stablelead-206 is formed.

25. Inferring A film badge consists of a piece of filmwrapped in a piece of dark plastic or paper. Dosesof what kinds of radiation can be measured withthis simple piece of equipment? Explain.

26. Calculating The first sample of californium wasmade by bombarding a target isotope with alphaparticles. In addition to californium-245, thereaction produced a neutron. What was thetarget isotope?

27. Calculating After 36.9 years, a sample ofhydrogen-3 contains one eighth of the amountit contained originally. What is the half-life ofthe isotope?

Math Skills

Critical Thinking

For: Self-grading assessment

Visit: PHSchool.com

Web Code: cca-1100

23892U 234

90Th 23491Pa 234

92U

21884Po 222

86Rn 22688Ra 230

90Th

α

21482Pb 214

83Bi 21484Po 210

82Pb

α

20682Pb

Stable isotope

21084Po 210

83Bi

β, γ

α β, γ β, γ

α, γα, γα

β, γ β, γ α

βα

28. Calculating The half-life of iron-59 is 44.5 days.After 133.5 days, 2.76 g of iron-59 remains.What was the mass of the original sample?

29. Inferring The beta emissions from a bone thatwas found buried in a cave indicate that thereare 4.6 carbon-14 decays per gram of carbonper minute. A chicken bone from a fast-foodrestaurant shows 18.4 emissions per gram ofcarbon per minute. How old is the bone fromthe cave?

30. Inferring Radioisotopes are commonly used inmedical tests to diagnose diseases. Do theradioisotopes used for this purpose have longhalf-lives or short half-lives? Explain.

31. Applying Concepts Americium-241 andradon-222 both emit alpha particles. Americiumis found in almost every home as a component ofsmoke detectors. But radon is considered ahealth hazard. Why is radon more hazardous?

32. Making Judgments If a fusion power plantcould be constructed, why might it be a bettersource of energy than a fission plant?

33. Writing in Science Write a paragraphexplaining how radon gas can collect in buildings.(Hint: The first sentence in your paragraph shouldstate the paragraph’s main idea.)

Evaluating Many transuranium elements werenamed for the scientists who synthesized them or thelocation in which they were produced. Choose such atransuranium element, find out how it was created, andevaluate its importance. Write a pamphlet informingyour classmates about the element you chose.

Performance-Based Assessment

Concepts in Action

320 Chapter 10

Critical Thinking23. U-238 to Th-234, alpha; Th-234 toPa-234, beta and gamma; Pa-234 to U-234, beta and gamma; U-234 to Th-230, alpha; Th-230 to Ra-226, alphaand gamma; Ra-226 to Rn-222, alphaand gamma.24. Polonium undergoes alpha decay.Bismuth and lead undergo either betadecay or beta decay and gamma decay.25. Beta radiation or gamma radiation.The plastic or paper wrapped aroundthe film blocks exposure to alpharadiation.26. Curium-242

Math Skills 27. 12.3 years28. 22.1 grams29. 11,460 years (equivalent to two half-lives of carbon-14)

Concepts in Action30. Radioisotopes used as radioactivetracers have short enough half-lives so asto limit the patient’s exposure to nuclearradiation, but long enough half-lives topermit the diagnostic test.31. Because radon-222 is a gas, it can be ingested by breathing and causeinternal radiation exposure. Americium-241 is a solid that cannot be ingested bybreathing.32. Fusion releases more energy thanfission, uses a more available fuel source(hydrogen), and does not produceradioactive wastes.33. Radon is a naturally occurringradioactive gas produced by the nucleardecay of uranium found in rocks andsoil. Because it is a gas, radon can seepinto a building through cracks andpinholes in the building’s foundation. Ifthe basement of the building is notventilated properly, the radon cancontinue to accumulate, increasing therisk of radiation exposure.

Chapter 10

Performance-Based AssessmentStudents will discover that elements with atomicnumbers 96 and 99 onwards were named afterthe scientists who discovered them. Elementswith the atomic numbers 95, 97, and 98 werenamed after the locations in which they werediscovered.

Your students can independentlytest their knowledge of the chapterand print out their test results foryour files.

Nuclear Chemisty 321

Standardized Test Prep

Choose the letter that best answers the question orcompletes the statement.

1. Which equation correctly shows beta decay?(A) Pb S Tl � e � �(B) Pb S Bi � e � �(C) Pb S Tl � e � �(D) Pb S Bi � �(E) Pb S Bi � e � �

2. The half-life of radon-222 is 3.8 days. If a samplecurrently has 3.1 grams of radon-222, how muchradon-222 did this sample have 15.2 days ago?(A) 12.4 grams (B) 47.1 grams(C) 49.6 grams (D) 57.8 grams(E) 92.7 grams

3. Radioactive decay of nuclei often involves severaldecays before a stable nucleus is formed. This iscalled a decay chain. What stable isotope isformed when radon-222 undergoes a decaychain of four alpha decays followed by fourbeta decays?(A) tungsten-206 (B) platinum-206(C) lead-206 (D) tungsten-214(E) lead-214

4. Which nucleus balances the following nuclearequation for the fission of uranium-235?

U � n S Sr � X � 2 n � �(A) Xe (B) Te(C) Te (D) Xe(E) Sn142

50

14454

14452

14652

14654

10

AZ

9038

10

23592

0�1

21083

21082

21083

21082

0�1

21083

21082

0�1

20983

21082

0�1

20981

21082

5. Uranium-238 is less stable than oxygen-16. Whataccounts for this difference?(A) Uranium is a solid, while oxygen is a gas.(B) Unlike oxygen-16, uranium-238 has a

nucleus in which repulsive electric forcessurpass the strong nuclear forces.

(C) Oxygen-16 has fewer electrons thanuranium-238.

(D) Uranium-238 has fewer neutrons thanoxygen-16.

(E) Unlike uranium-238, oxygen-16 has anucleus in which the strong nuclear forcesare overcome by repulsive electric forces.

6. The primary source of energy in stars is the fusionof hydrogen into helium. However, anotherreaction is believed to occur simultaneously. It iscalled the carbon-nitrogen-oxygen (CNO) cycle.In the diagram below, the symbol e representsa positron. A positron is a particle that has thesame mass as an electron but a charge of 1�.

Which equation describes the CNO cycle?(A) H S He � e (B) 4 H S He � 2 e(C) H � H S He � n(D) C S C � He(E) C � H S C � He 4

2126

11

126

42

126

126

10

42

31

21

0�1

42

11

0�1

42

11

0�1

Test-Taking Tip

Evaluating and RevisingFrequently, a scientifically accurate answer choicemay not answer the question that is being asked.Keep these tips in mind:

• Verify what the question is asking.

• Determine if an answer choice is a truestatement or not.

• Determine if a true answer choice actuallyanswers the question.

• Be cautious with inserted or deleted wordsthat make a false statement seem accurate.

Practice using these tips in Question 5.

N137

He42

C126

e0+1

H11

H11

H11

H11

e0+1

N157

O158

C136

N147

Standardized Test Prep 1. E 2. C 3. C4. D 5. B 6. B



section 10.1 10.1 radioactivity...nuclear chemistry 293 radioisotopes of uranium—primarily...

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