10 radioactivity

SEK MEN SAINS MUZAFFAR SYAH

214

Matter is made up of very small particles called _________ Each atom has a very small and very dense core called ________. Most

of the mass of atom is contained in the __________. The __________ move in orbits around the nucleus. There are a lot of empty __________ within atom A nucleus consists of a number of __________ and ____________. Protons and neutrons also known as __________. A proton has a ___________ charge. A neutron is a ___________ particle of about the same mass as the

proton. An atom is _________ because it contains an equal number of

negatively charged electrons. So the net charge is zero.

Proton number, Z, is defined as the number of protons in a nucleus.The number of protons = the number of electronsAn element is identified by its proton number

Nucleon number, A is defined as the total number of protons and neutronsin a nucleus. It is also known as mass number.Nucleon number, A = number of proton Z + number of neutrons

A nuclide is an atom of a particular structure. Each element has nucleuswith a specific number of protons.

Proton p11

Neutron n10

Electron e01

AX A = nucleon number

Z Z = proton numberX = chemical symbol of the element

Example C126

Proton number of carbon = ___,Number of proton = _____ Number of electron = ___Number of neutron = ______

Isotopes are atoms with the same proton number but different nucleonnumber. Isotopes of an element contain the same number of protons and the

same number of electrons. So isotopes have the same chemicalproperties chemical reactions involve the electrons in an atom.

However they have different physical properties because their mass isdifferent.

Some isotopes exist naturally. Isotopes can also be made artificially.

Example: H11 hydrogen H2

1 deuterium H31 tritium

10.1

Describe thecompositionof thenucleus ofan atom interms ofprotons andneutrons

Defineprotonnumber (Z)

Definenucleonnumber (A)

What isnuclide

DefineIsotopes

Nuclide

notation XAZ


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Dalton’s modelMatter was made up of very small particles calledatoms.Atoms can neither created or destroyed.All atoms of the same element are identical;different elements have different types of atom.

Thomson’s model – plum-pudding model

Atom is a solid sphere of positive charge withelectrons distributed uniformly over it.

Rutherford modelAn atom has a positively charged core or nucleus,which contains most of the mass the atom andwhich surrounded by orbiting electrons.

Geiger and Marsden planned and carried out anexperiment proposed by Sir Ernest Rutherfordand found evidence for Rutherford Model.They fired a stream of alpha particles at a verythin gold foil and counted how many alphaparticles were scattered at a number of differentangles. The results agreed well with the theory.

The result and the conclusion of the experimentis simplified in the table below:

Result ConclusionMost of the alphaparticles passed straightthrough the foil in theiroriginal direction.

Most of the space takenup by an atom must becompletely empty. Avery small nucleus isplaced at the centre ofthe atom.

A few alphas particleswere deflected throughvery small angles

The nucleus arepositively charged. Thealpha particles alsopositively charged arerepelled by the nucleusbecause repulsion forceis produced between thelike electric charges.

A very small number ofalpha particles werebounced back by thegold foil.

When the alpha particlesapproach very close tothe nucleus , they wereexerted by a very largerepulsion force becausethe repulsion obeys theinverse square law ofthe force between twocharged objects( F 1 )

r2

Bohr’s modelBohr’s model state that an atom has electrons instable orbits around the nucleus , like planetsround the sun.

Chadwick’s modelThe neutron as a neutral particle found in thenucleus of atoms , along with the protons.

ATOMIC MODEL


215

Today’s model of the atom

The atom with its very small and very densenucleus surrounded by a cloud of negativeelectrons. The electrons may be represented as‘waves’ or ‘clouds’ around the nucleus. Thenucleus is made up of protons and neutrons orcalled nucleons.

Protons, neutrons and electrons are thefundamental particles of an atom.

TUTORIAL 10.1

1. A nucleus consists ofA. protons and electronsB. protons and neutronsC. neutrons and electronsD. neutrons only

2. A negatively charged particle movestowards a nucleus of an atom. Which ofthe following diagrams shows the correctpath of the particles? (2007)

3. The nuclide of a lithium atom is written

as Li73 . What is the number of protons,

nucleons and electrons in a neutrallithium atom?

Numberof

protons

Numberof

nucleons

Numberof

electronA 4 7 3B 3 4 7C 4 3 4D 3 7 3

4. Which nuclide notation represents anuclide which has 30 protons and 35neutrons?

A. X3530 C. X65

30

B. X6535 D. X30

35

5. The proton numbers and nucleonnumbers of three nuclei P, Q and R areas shown in Table 1.

Nucleus Protonnumber

Nucleonnumber

P 52 86Q 53 87R 52 87

Which nuclei are isotopes of the sameelement?A. P and Q onlyB. P and R onlyC. Q and R onlyD. P, Q and R


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6. The diagram shows the ‘plum pudding’model of an atom.

(a) Scientists thought that the‘pudding’ was positively charged.(i) Name the particles labelled A in

the diagram.

____________________________

(ii) Complete this sentence bychoosing the correct wordsfrom the box.

The particles labelled A are

___________________________

(b) A new model of an atom wassuggested by Rutherford andMarsden. They fired alpha particlesat thin metal foil. Alpha particles arepositively charged. In their modeleach atom has a nucleus.The diagram below shows the pathof an alpha particle as it passes thenucleus of an atom.

(i) Explain why the alpha particlechanges direction.

___________________________

___________________________

___________________________

(ii) The diagram shows differentpaths taken by alpha particleswhen they were fired byRutherford and Marsden at thethin metal foil.

The boxes on the left show someobservations from the experiment.

The boxes on the right give theirexplanations.Draw a straight line from eachobservation to its explanation.One has been done for you.

Observation Explanation

negatively chargedpositively chargeduncharged

because thenucleus has avery largepositive chargeand a largemass

some alphaparticles travelalong path Y

most of thealpha particlesfollow path X

because thenucleus is verysmall

some alphaparticlesreboundbackwardsalong path Z

because mostof each atom isemptyspace

very few alphaparticles followpath

because thenucleus ispositivelycharged


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Radioactivity is the spontaneous disintegration (decay) of an unstablenucleus into a more stable nucleus accompanied by the emission of energeticparticles (radioactive rays) or photons .

The nuclei of some atoms are unstable. The nucleus of an unstable atomwill decay to become more stable by emitting radiation in the form of aparticle or electromagnetic radiation.

Random process means there is no way to tell which nucleus will decay,and cannot predict when it is going to decay.

A spontaneous process means the process is not triggered by anyexternal factors such as temperature of pressure.

3 kinds of Radioactive emmsion :Alpha particle, Beta particle and Gamma radiation

Characteristic Alpha Beta Gamma

Nature Helium nuclei or

He42 2 p and 2 n

Electrons, e01

Electromagneticradiation.

Mass 4 1/2000 0

Charge +2e -e Neutral

Speed Slow Fast Speed of light

Ionizing ability High Medium Low

Penetrating power Low Medium High

Stopped by A few cm of air a pieceof paper

A few mm ofaluminium foil

A few cm of lead

Deflected by electricand magnetic fields Yes Yes No

10.2

State whatradioactivityis

Compare the 3 kinds of radioactive emissions in terms of their nature


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Ionizing effect

Visible tracks in acloud chamberfor alpha particle,beta particle andgamma rays

Radioactive emission has an ionizing effect The 3 types of radiation are highly energetic and use their energy to

remove electrons from the air molecules when they pass through air. The ionization of an atom produces positive ion and negative ion

(electron) Due to their different charges and masses, they have different ionizing

abilities.

Alpha Beta Gamma

Dense – strongionization powerstraight tracks - thealpha particle has alarge mass andmomentum so it is noteasily deflected

Very fast beta particles- thin, straight tracks.The slower betaparticles - short, thicktracks which curve inrandom direction.

The gamma rays donot produce clear orcontinuous tracks dueto their low ionizingpower

Penetratingpower

The penetrating effect of alpha, beta and gamma radiation depends ontheir ionizing power.

Radiation which has a stronger ionizing power will have a lowerpenetrating effect.

The radiation emission loses some of its energy each time an ion pair isproduced.

Alpha particles lose energy very quick as they move through a medium.After a short distance in the medium, the alpha particles would have lostalmost all energy. So alpha particles have the lowest penetrating power.

Alpha particles can be stopped by paper, beta particles go through paperbut can be stopped by thin metal. Gamma rays can go through paper andmetal sheet and can only be stopped by thick lead or concrete.


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Interaction withelectrical field

Alpha and beta particles are deflected in an electric field because they arecharged. The deflections are in opposite direction because they carryopposite charges. The deflection of beta is larger than alpha becausemass of beta < mass of alpha

Gamma rays are not deflected because they do not carry any charge.

Interaction withmagnetic field

Alpha particles and beta particlesare also deflected when they passthrough a magnetic field whilegamma rays are unaffected.

The direction of the deflection ofalpha particles in the magnetic fieldcan be found using Fleming’s left-hand rule.

Gold leaf electroscope When an electroscope is charged, the gold leaf sticks out,

because the charges on the gold repel the charges on themetal stalk.

When a radioactive source comes near, the air is ionized andstarts to conduct electricity.

This means the charge can ‘leak’ away, the electroscopedischarges and the gold leaf falls.

Photographic Badge Is worn by worker in nuclear power stations and

in radiation laboratories. The badge contains a photographic film in a light-

proof packet

The parts of the film which hadreceived radiation will be darkened.The degree of darkening indicates theamount of radiation the person hadbeen exposed to.

Name common detectors for radioactive emissions


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Geiger-Muller tube (GM tube) The radioactive emission enters the tube through

the mica window and ionizes the neon gas. The electrons and positive ions are attracted

towards the anode and cathode respectively. When electrons are collected by the anode, a

pulse of current is produces. The pulses of current are counted by a scaler or

ratemeter. The scaler gives the number of counts over a

certain period of time ie counts per minute /counts per second.

Initially the GM tube is switched on without thepresence of any radioactive substance. Thereading displayed by the ratemeter is known asthe background count rates.

When the GM tube is used to detect radioactiveemission, the background count rate issubtracted from the count rate obtained.

Actual reading = Reading recorded –Background Reading.

Notes:Background radiation gives reading to theGM tube even though there is noradioactive source.Background radiation is always presentdue to natural radioactivity in the ground,bricks or buildings and cosmic radiation.

Cloud Chamber It shows the path traveled by the ionizing

radiation in air. The radioactive produces ions in the air that is

saturated with alcohol vapour. The alcohol vapour condenses on the ions to

make the tracks of the radiation visible. Alphaparticles are best for this because it ionizationpower is high.

Spark counter The spark counter consists of a wire gauze and a

thin wire below it. A high voltage is applied between the gauze and

the wire. The voltage is adjusted until it is justbelow the value required to produce sparks.

When a radioactive source is brought near thewire gauze, the radiation ionizes the air below it.The motion of the ions to the gauze and the wirecauses sparks to be produced. The spark can be seen and heard.

Spark counters are suitable for alphaparticles. Beta particles and gammarays produce too few ions to producesparks.


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Radioactive decay is the process by which unstable atomic nuclei emitsubatomic particles or radiation. When a radioactive nucleus decays, its nucleus breaks up, emits an alpha

particle or beta particle and energy, and forms a new atom of a differentelement.

The nucleus before the decay is called the parent nuclide and the productof the decay is the daughter nuclide.

A parent nuclide X changes into a daughter nuclide Y.

Alpha decay Beta decay Gamma decay

The daughter nuclide has 2protons less and 2 neutrons lessthan the parent nuclide.The proton number Z decreasesby 2 and its nucleon number Adecreases by 4

A neutron changes to protonand electron during beta decay.Proton stays within the nucleusand electron is emitted as betaparticle.The nucleus loses a neutronbut gains a proton.Proton number increase by 1 ,nucleon number remainsunchanged

Gamma emission does notchange the structure of thenucleus, it just makes thenucleus more stable.Gamma rays are emitted atthe same time togetherwith either an alpha or betaparticle. When a nucleusejects an alpha or betaparticle, there is oftensome excess energyproduced which will bereleased as gamma rays

HeTh 42

22688

23090 + energy

HeThU 42

23490

23892 + energy

eNC 01

147

146 + energy

eBiPb 01

20983

20982 + energy

HePbPo 42

20682

21084

CoCo 6027

6027

Sometimes the daughter nuclide of a radioactive does is stillunstable. It will eventually decay into another nuclide which is alsounstable.

This process continues as a radioactive decay series until a stablenuclide is reached.

Each decay will emit either an alpha particle or a beta particle andmay be gamma rays.

Explainwhat isradio-activedecay?

What isradioactivedecayseries

Use equations to represent changes in the composition of the nucleus whenparticle are emitted


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Example 1

Uranium-238 ( U23892 ) emits an alpha particle and

decays into a thorium atom. State the nucleonnumber and proton number of the thorium, Theisotope formed. Write an equation for this decay.

Example 2Complete:210 0Pb Bi + e

82 -1

Example 3

Strontium-90 ( Sr9038 ) decays to yttrium-90 ( Y90

39 )

by emitting a radioactive particle.(a) write an equation for this decay.(b) What particle is emitted during the decay?

Example 4232

Th decays to208

Pb ,90 82

by emitting alpha particles and betaparticles. Determine the number of alphaparticles and beta particles being emitte?

Example 5

The uranium isotope U23892 decays into a stable

lead isotope through successive emissions of 8alpha particles and 6 electrons. What is the protonnumber and the nucleon number of the leadisotope?

Example 6Both alpha and beta particles are produced

when M23490 decays to N218

92 . How many

alpha and beta particles are produced.

Example 7A nuclide

232V decays to nuclide

220W

92 90

and emits alphaparticles and beta-particles. How many alpha and betaparticles are produced?

Example 8The diagram shows part of a radioactive decayseries. Name the particles or radiations are emittedat part I, II and III.

Example 9 (SPM 2004 paper 1)The diagram shows a series of radioactive

decays for the nucleus of uranium-238to that of radium-226.

What is the number of the alphaparticles and beta particles emittedduring this process?


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The decay curve for the radioactive gas radon-222which has a half-life of 55 seconds.

A radioactive nuclide with ashorter half-life will decay at afaster rate than anotherradioactive nuclide that has alonger half-life.

Example 1The radioactive atoms in a substance decay tobecome stable atoms. It was found that after 288s, 6.25% of the atoms have not decayed. What isthe half-life of the substance?

Example 2The half-life of iodine-131 is 8 days. Aradioactive sample contains 64 g of iodine-131. Determine the mass of iodine that hasdecayed and has not decayed after 24 days.

Example 3A sample of lead-211 of mass 96 g has a half-life of36.1 minutes.(a) What fraction of the sample has not decayed

after 108.3 minutes?(b) What is the mass of the decayed products after

this period of time?

The half-life T1/2 of a radioactive substance is the time taken for the numberof undecayed nuclei to be reduced to half of its original number.

The activity of a radioactive substance is the number of decays persecond of the unstable nuclei. It is also known as the decay rate.

Each decay corresponds to the emission of one particle or one photon

As the number of undecayed nuclei decreases with time, the activity ofthe radioactive substance also decreases with time.

The activity can be measured by using a GM tube connected to aratemeter

The SI unit for activity is the Becquerel (Bq). 1 Bq = 1 decay per second

Explainhalf-life

Determinethe half-life from adecaycurve


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Example 4The figure shows the decay curve for a radioactivesample.

(a) What is the half-life of the sample?(b) State the value of T.

Example 5The diagram shows a graph activity againsttime for a radioactive element. What is itsactivity after 12 hours?

Example 6The activity of a radioactive sample is reduced to

16

1of its initial value after 156 minutes. What is

the half life of the sample?

Example 7The table shows the count rate recordedfrom a radioactive substance at two differenttimes on the same day. What is the half-lifeof the substance?

Time Count rate2.00 pm 340 per second5.40 pm 85 per second

TUTORIAL 10.2

1. The diagram shows the path ofradioactive rays, S and T.

Which of the following shows the type ofray S and ray T? (2003)

2. The table shows the half-lives ofradioisotopes J, K, L and M.

Radioisotopes Half-lifeJKLM

8 days56 days

5.27 years6 hours

Which of the radioisotope is mostsuitable as a tracer in the human body?(2003)A. JB. KC. LD. M


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3. Which of the following has a similarcharacteristic to β particles? (2004)A. ProtonB. ElectronC. Helium nucleusD. Electromagnetic wave

4. Which of the following statements is acharacteristic of gamma radiation? (2005)A. It has a positive chargeB. It is an electromagnetic waveC. It has a higher ionizing power than

alpha radiationD. It has a lower penetrating power than

beta radiation

5. The following equation represents thedecay of a uranium nucleus.

HeyexThU 42

01

23090

23892

What are the values of x and y? (2005)

X YA 0 1B 1 1C 1 2D 2 2

6. The initial mass of radioactive element is10 g and its half-life is 6 days. Which ofthe following statements about the massof the radioactive element is true? (2006)A. 6 days earlier, the mass is 20 gB. 12 days earlier, the mass is 80 gC. 6 days later, the mass is 2.5 gD. 12 days later, the mass is 5.0 g

7. The graph shows the decay curve of aradioactive material.

If the initial of the radioactive material is800 counts per minute, what is theactivity after 1 hour? (2004)A. 400 D. 200B. 100 E. 50C. 25

8. Three different rays P,Q and R areemitted from a radioactive substance.The following table shows thecharacteristics of the rays.

Type ofrays

P Q R

Deflectionof thegold leafof anelectro-scope.

unchanged unchanged decreases

Effect onSparkCounter

no spark no sparks producesparks

Tracks incloudchamber

Penetrating power

A few cmof lead canabsorb asignificantamount ofit

Stoppedby a fewmm ofaluminium

Stoppedby a sheetof paper

Based on the graph above,(a) State the nature characteristic of rays

(i) P

_____________________________

(ii) Q___________________________

(b) Which of the rays has the strongestpenetrating power?

______________________________

Explain why(i) rays P can produce sparks in a

spark counter?

___________________________

___________________________

(ii) rays P and Q cannot bedetected by a gold leafelectroscope?

__________________________

__________________________


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(d) Explain why rays R producethick and straight tracks incloud chamber?

___________________________

9. A radioactive source contains an isotope

of thorium.Thorium ( Th22890 ) decays by -

particle emission to radium (Ra).Write an equation to show this decay.

(b) The radium produced is alsoradioactive. Diagram 1 shows alaboratory experiment to test for thepresence of the radioactiveemissions from the thorium source,using a radiation detector. In thelaboratory there is a backgroundcount of 20 counts/minute.

The readings are given in the table.

Position Reading in count /per minute

P 2372Q 361

State and explain(i) which radiation could be

causing the count at Q,

___________________________

___________________________

___________________________

___________________________

(ii) which radiations could becausing the count at P.

___________________________

___________________________

(c) All three types of radioactiveemission cause some ionisation ofgases.(i) Explain what is meant by the

term ionisation of gases.

___________________________

___________________________

___________________________

(ii) Suggest a reason why -radiation produces very littleionisation.

___________________________

___________________________

10. The diagram shows part of238

U decayseries.

Based on the diagram above;

(a) Name the rays or particles emittedwhen

234Th decays to

234Pa

90 91

_______________________________

(b) State a pair of an isotope.

________________________________

(c) The half life of Pa23491 is 6.7 hours and

Initially has a mass 32 g. What isthe mass of Pa-234 after 33.5hours?


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11. Diagram 1 and Diagram 2 show the rateof decay of radioactive substances,flourine-22 and sodium-24.

(a) Based on the decay curves of flourine-22 and sodium-24,(i) state a common characteristic for

the change in activity in relation totime for the decay of flourine-22and sodium-24.

______________________________

______________________________

______________________________

______________________________

______________________________

(ii) complete the table below

Activity/Countperminute

2000 1000 500 250

Decaytime offluorine-22/ s

0 4 8

Decaytime ofsodium-24/ s

0 1 2

(b) What happens to the activity of(i) flourine-22 after every 4 s?

____________________________

____________________________

(ii) sodium-24 after every 1 s?

____________________________

____________________________

(c) Based on the answers in (b)(i) and(b)(ii), draw a conclusion from theactivity change with time for these twosources to form a physics concept.

_________________________________

_________________________________

_________________________________

_________________________________

(d) When flourine-22 decays, it produces abeta particle and neon-22 (Ne).(i) What is a beta particle?

______________________________

(ii) Complete the following equation forthe decay of fluorine-22.

........NeFl ..............

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In industries(c) Smoke detectors Contain a weak radioactive source such as americium-

241. Alpha particles emitted from the source ionize air

molecules. The ionized air molecules conduct electricityand a small current flows in the smoke detector.

When smoke enters the detector, the soot particles in thesmoke absorb some of the alpha particles.

This causes a decrease in the current that flows in thesmoke detector and trigger the alarm.

Americium-241 has a long half-life, 460 years so that thesubstance will last longer.

(b)Thickness control A radioactive sends radiation through the sheet

material as it comes off the production line.Beta radiation are used for thin sheets. Aradiation detector on the other side of the sheetmeasures the intensity of the radiation passingthrough the sheet.

The amount of radiation received by the detectordepends on the thickness of the rubber sheet.

If the sheet is too thin, the reading of thedetector increases.

A signal is sent from the roller control to the rollers so that the pressure on the sheets can bereduced.

(c) detecting leaks in underground water pipes. A radioactive substance which emits beta

particles is added to a fluid in a pipeline tomeasure the flow rate in the pipeline and to findleaks.

The radiation produced by the radioactivesubstance can be detected with a GM tubecounter placed above ground.

A larger increase in the count rate will indicatethat there is leak in that area.

10.3

Radioisotopes are unstable isotopes which decay and give outradioactive emissions.

Radioisotopes are isotopes of an element that are radioactive. Radioisotopes are naturally occurring or artificially produced.

Defineradioisotopes.

Describe applications of radioisotopes


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Medicine(a) Radioactive tracers Nuclear medicine is a branch of

medicine that uses radiation toprovide information about thefunction of the specific organs of apatient or to treat disease.

Characteristics of radioisotope:(a) half-life is medium, long enough

to examine metabolic processesin the body and short enough tominimize the radiation dose tothe patient.

A radioisotope is taken in by a patient through thedigestive system, by inhalation or through theblood vessels by injection.

The radiation emitted enables organs such asthyroid, bones, heart, liver to be easily imaged byimaging equipment. Disorders can then bedetected.(b) emits low energy gamma rays which can

pass through the body without muchionization of the molecules.

(b)Sterilizing medical instruments are sterilized

after packing by a brief exposure togamma rays.

Gamma rays can be used to killbacteria, mould and insects in food.

(c)cancer treatment Gamma rays can kill living cells. They are used to

kill cancer cells without having to resort tosurgery.

This is called radiotherapy. It is important to administer the correct dosage.

Excessive radiation will damage too many healthycells. Insufficient radiation will not stop thecancer from spreading.

Application of radioisotope in thefield of agriculture By measuring the radioactivity of the

stem and leaves, scientists can findout how much fertilizer has beenabsorbed by the plant.

Radioisotopes are used to kill pestsand parasites and to control theripening of fruits.

Application of radioisotope in archaeology Carbon-14 is a radioisotope with a half-life of 5730

years and decays by emitting beta particles. Living animals and plants have a known

proportion of carbon-14 in their tissues whichremains constant.

When living things die, the amount of carbon-14in their body decreases at a known rate.

The amount of carbon-14 left in a decayed plant oranimal can be used to tell its age.

TUTORIAL 10.3

1. Which statement is true about the use ofradioactive substance? (2006)A To determine the sex of a foetusB To identify counterfeit bank – notesC To detect leakage in underground

pipesD To determine the contents in

baggage of air plane passengers

2. Cobalt-60 destroys cancer cells becauseit….. (2003)

A. has a long half-lifeB. has no side effectC. radiates gamma raysD. decays spontaneously

3. What is the radioisotope that can be usedto determine the age of a fossil? (2005)

A. Radon-222B. Uranium-238C. Carbon-14D. Iodine-131

4. Xenon-133 is used in studying lungfunction because itA has a long half-lifeB has no side effectC emits alpha or beta particlesD emits radiation with low ionization

power


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5. Radioisotope that can be added into thewater isA Carbon-14B Iodine-131C Sodium-24D Phosphorus-32

6. The diagram shows a logic gate systemis used in a factory to ensure the volumeof paint in containers is within thepredetermined range.

Which type of ray is emitted from theradioactive source?A Alpha particleB Beta particleC Gamma ray

7. The diagram shows the structure of asmoke alarm.

Which of the following is true?A Cobalt -60 is used as a radioactive

source.B The device works based on the

penetrating power of theradioactive radiation

C When a fire breaks out, the particlesof smoke will absorbs the alphaparticles

D The particles of smoke increase theionisation of the air and the alarmwill be activated

8. The diagram shows a graph of activity ofIodin -131 present in the thyroid againsttime of three patients P, Q and R whenthe Iodin-131 are injected into the body ofthe patients.

Who is has a normal thyroid gland?A Patient PB Patient QC Patient R

9. What is the radioisotope that can be usedto determine the age of a fossil?A Carbon-14B Iodine-131C Radon-222D Uranium -238

10. Which of the following is the Hazardsymbol of a radioactive substance?

11. Which of the following factor is notaffecting the severity of radiation ?A Types of radiationB Dosage and exposure timeC Methods of insertion into the bodyD The temperature of the radioactive

source


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12. When some fresh foods are exposed toγ-rays, the foods keeping qualities areimproved and the foods are safe to eat.Why can people eat these foods withoutsuffering from the effect of radiation?A γ-rays have very low energyB γ-rays carry no electric chargeC γ-rays have a very short half-lifeD γ-rays do not make the food

radioactive

13. Table below shows the half-lives of fourtypes of liquid isotopes which radiate βparticles.

Isotope Half-lifeP 10 secondsQ 20 hoursR 5 monthsS 10 years

Which of the following isotopes issuitable to detect blood clotting? (2007)A. PB. QC. RD. S

14. Why are radioactive sources stored inboxes lined with lead?A Lead absorbs radiation and stops it

from escaping into the roomB Lead absorbs the radioactive source

and make it safe to handleC Lead slow down the rate at which the

radioactive source decaysD Lead completely stops the source

from decaying and so it lasts longer

15. The diagram shows a radioactive sourceand a detector are used to check thelevel of fruit juice in a carton. Cartons offruit juice pass between the detector andthe radioactive source. The radioactivesource emits β- particles.

(a) State the name of a suitabledetector of the β- particles.

______________________________

(b) What is a β- particle?

______________________________

(c) Explain why the level of detectedradiation falls when a full carton ofjuice goes past the detector?

______________________________

(d) Explain(i) why a source emitting α -

particles is not used.

__________________________

___________________________

___________________________

(ii) why a source emitting γ - raysis not used.

___________________________

___________________________

16. The diagram shows the process ofcontrolling the thickness of metal plates.

The reading obtained are shown in thetable below:

Positionof metalplate

A B C D E F

Readingofcounter /count perminute

200 250 180 202 197 201


233

(a) Name the detector P.

__________________________________

(b) Why the gamma source is used?

__________________________________

(c) Why the gamma source is placed in aplumbum box?

__________________________________

__________________________________.

(d)(i) At what position of the metal is verythin ?

________________________________

(ii) Give one reason for your answer ind(ii).

________________________________

________________________________

(e) Explain why the thickness of the metalplate at position A,D,E and F are samebut give the different readings?

_________________________________

(f) What happen to reading of the counterif a part of the metal plate attached withmagnet?

_________________________________.

(g)(i) If the gamma source is removed,what happen to the reading of thecounter?

________________________________

(ii) Give the reason for your answer ing(i).

________________________________

________________________________

17. Diagram(a) shows a box containing adangerous material.

Diagram (a)

(i) What is material is kept in the box?

________________________________

(ii) State one negative effect of thematerial to the people?

________________________________

(iii) Give two safety precautions whichshould be taken when handling thematerial?

_______________________________

_______________________________

(b) A doctor uses radioactive rays todetect the flow of blood in a patient.The device is shown in Diagram (a)and its results recorded are shownin Diagram(b).

Diagram(a)

Diagram (b)


234

(i) Name a radioisotope is used.

________________________________

(ii) State the type of radioactive rayemitted.

________________________________

(iii) The radioisotope used has a shorthalf-life. Explain why?

________________________________

________________________________

(iv) Why is there a peak in the graph?

________________________________

________________________________

________________________________

(c) A detector shows the activity of aradioisotope decreases from 160counts per second to 20 counts persecond in 15 minutes. Calculate thehalf-life of the radioisotope.

SPM 200718. Diagram 8 shows a system used in a

factory to ensure the thickness of acardboard sheet is uniform.

The radioactive source, radiationdetector and counter are used to detectthe thickness of cardboard sheet. Theradioactive source contains aradioisotope. The roller is used tocompress the cardboard sheet.Table 8 shows four radioisotopes withtheir respective properties.

Radioisotpes Half-life

Type ofradiation

Physicalstate

Sodium-24 15hours

Gamma Liquid

Phosphorus32

14.3days

Beta Liquid

Cobalt -60 5.27years

Gamma Solid

Strontium 90 28.5years

Beta Solid

(a) What is meant by a radioisotope?

________________________________

(b) Based on Table 8, state the suitableproperties of the radioisotope todetect the thickness of the cardboardsheet.

(i) Half-life

_____________________________

Reason

_____________________________

(ii) Type of radiation

_____________________________

Reason

_____________________________

(iii) Physical state

_____________________________

Reason

_____________________________

(c) Based on the answers in 8(b),determine the most suitableradioisotope in Table 8 to detect thethickness of the cardboard sheet.

________________________________

(d) The radioisotope in 8(c) is used todetect the thickness of the cardboardsheet.


235

(i) State the change in the reading ofthe counter when a thickercardboard is used.

_____________________________

(ii) How is the thickness of thecardboard sheet reduced?

_____________________________

(e) The half-life of Cobalt-60 is 5.27years. Calculate the time taken forthe activity of Cobalt 60 to reduce to6.25 % of its initial value.

SPM 200319. As a researcher , you are assigned to

investigate the characteristics of acertain radioactive isotope that couldbe used to detect the thickness of paperin a paper factory.(a) What does the term isotope mean?

(b) The table below shows thecharacteristics of five isotopes.

Characteristics of isotopeIsotope

Stateofmatter

Emittedradiation

Half-life

Penetrating power

Strontium-90

Solid Beta 28year

s

Medium

Cobalt-60 Solid Gamma

5year

s

High

Xenon-133

Gas Beta 5day

s

High

Watercontaining H-3

Liquid Beta 12year

s

Medium

Polonium-210

Solid Alpha 140day

s

Low

Based on the table above;

(i) Explain the suitablecharacteristics of the isotopesso that it can be used tomeasure the thickness of paperin a paper industry.

(ii) Select the most suitableisotope to be used in detectingthe thickness of paper in thefactory and give your reason.

(c) Suggest briefly the arrangement ofthe paper thickness detectorapparatus and state howradioactivity is used to detect thethickness of the paper.

(d) Sketch a graph activity against timeto illustrate how radioactivematerials decay. Use your graph toexplain how the half-life isdetermined.

(e) The half-life of cobalt-60 is 5 years.Calculate the time taken for theactivity of this isotope to decay to12.5% of its initial value.

SPM 200420. A paint-producing factory wants to

develop a volume control system whichcan ensure the quantity of paint in everythin is within in a specific range. The tinsof paint are transported on a conveyorbelt as shown in diagram below. If thevolume of the paint is less or more thanthe specific range of volume, the tin willbe separated automatically.

Using your knowledge on theradioactivity and the Diagram above,explain;(a) the radioactive material and

equipment required to develop thevolume control system,

(b) how the equipment is assembled(c) how the system works


236

SPM 200621. Radioisotope material has some uses in

the medical field such as in theinvestigation of internal organs and inthe sterilisation of equipments.(a) A doctor conducts an investigation

on patient’s kidney by injectingiodine-131 radioisotope, that has ahalf-life of 8 days, into the bloodcirculation.A normal kidney can expel theradioisotope in 20 minutes.The presence of radioisotope in theleft and right kidneys is shown inthe graphs as in Diagram (a).

Diagram (a)

(i) What is meant by half-life?(ii) Based on the graphs in

Diagram(a), which kidney is notfunctioning properly?Give one reason.

(iii) The initial iodine-131 activity is1 600 counts per second.Calculate the time taken for theIodine- 131 activity to decreaseto 100 counts per second.

(b) Medical equipment is strelised byradiation from a radioactive source.You are assigned to study thecharacteristics of someradioisotopes that are suitable foruse in the strelisation of medicalequipments.

Table below shows thecharacteristics of fiveradioisotopes.

Radioisotope Characteristics of isotopeStateofmatter

Types ofray

Half-life

Strontium-90 Solid Beta 28 yearsCobalt-60 Solid Gamma 5 yearsXenon-133 Gas Beta 5 daysIodine- 131 Liquid Gamma 8 daysPolonium-210

Solid Alpha 140 days

(i) Explain the suitability of thecharacteristics to be used inthe strelisation of medicalequipment.

(ii) Determine the most suitableradioisotope to be used andgive one reason for yourchoice.

(c) Gamma rays can produce an effecton photographic film.Explain whether gamma rays issuitable to be used in takingphotographs of an organ in humans.

(d) Beryllium- 11 isotope emits two rays.The isotope is placed in front of anelectric field and the radioactiveradiation path is shown inDiagram(b).

Diagram(b)

(i) Name both rays that areemitted by the isotope.

(ii) Explain why the rays follow thepath shown


237

The atomic mass unit it the unit of mass for atoms and subatomic particlessuch as the proton, neutron an electron

1 atomic mass unit or 1 u is12

1of the mass of the carbon-12 atom.

The mass of one carbon-12 atom is 1.99265 x 10-26

kg

1 u =261099265.1

12

1 kg

1 u = 1.66 x 10-27

kg

Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei Fission occurs when the nucleus of an atom is bombarded with a neutron. The energy of the neutron causes the target nucleus to split into two (or

more) nuclei that are lighter than the parent nucleus, releasing a largeamount of energy during the process.

A slow neutron hitting a uranium-235 nucleus, causing it to split producingstrontium-90 , xenon-143 and three neutrons + energy.

energynSrXenU 10

9038

14354

10

23592 3

another reaction:

energynKrBanU 10

9236

14156

10

23592 3

The nucleus is divided into two large fragments of roughly equal mass There is a significant mass defect Other neutrons are emitted in the process

10.4

Defineatomicmass unita.m.u

Describenuclearfission

Giveexampleofnuclearfission

Differencebetweennuclearfission andradioactivedecay


238

Example of achain reaction

Critical mass

Graphite as amoderator

In the fission reactions, one neutron starts the fission process, but threeneutrons are produced.

If one of these neutrons bombards another uranium-235 nucleus then morefissions will occur, releasing more neutrons. A chain reaction is produced.

A chain reaction is a self-sustaining reaction in which the products of areaction can initiate another similar reaction.

As uranium atoms continue to split, a significant amount of energy isreleased during each reaction. The heat released is harnessed and used togenerate electrical energy

A controlled chain reaction is used in nuclear power stations An uncontrolled chain reaction is used in nuclear bombs.

In order for a chain reaction to occur, the sample of uranium must have acertain minimum mass known as critical mass

The neutrons produced in a fission reaction are very fast neutrons. Slowerneutrons are more easily captured by the uranium nuclei. Graphite can actas moderators to slow down the chain reaction to occur at a smaller criticalmass

Nuclear fusion is the combining of two lighter nuclei to form a heavier nucleus,releasing a vast amount of energy during the process.

Give examplesof nuclearfusion

Nuclear fusion is believed to be the process by which energy is released bythe Sun. When two hydrogen-2 nuclei moving at high speeds collide, theycan join together to produce heavier nucleus. A large amount of energy isreleased.

Describechainreactions

Describenuclearfusion


239

Another example:2 3 4 1H + H He + n + energy

1 1 2 0

energyHHeHeH 11

42

32

21

A hydrogen bomb uses the principle of nuclear fusion for its design.

Both nuclear fission and fusion release a large amount of energy. Thesource of this energy is from the loss of mass in nuclear reactions.

The sum of the masses of the particles before the reaction is more than thesum of the masses of the particles after the reaction.

Mass defect issum of the masses – sum of the massesbefore reaction after reaction

Mass and energy can be exchanged one for the other. A loss of mass in a nuclear reaction means that the mass had changed to

energy. The relationship between the mass and the energy:

E = mc2

Where E = energy released, in joules, Jm = loss of mass or mass defect, in kgc = speed of light = 3.0 x 10

8m/s

Example 1Below is an equation for the decay of radium-226.

energyHeRnRa 42

22286

22688

The masses of each atom:Ra-226 = 226.02536 a.m.uRn-222 = 222.01753 a.m.uHe-4 = 4.00260 a.m.u1 a.m.u = 1.66 x 10

-27kg

1 eV = 1.66 x 10-19

J

(a) Find the mass defect in(i) a.m.u (ii) kg

(b) Calculate the amount of energy released in(i) J (ii) eV

Relate therelease ofenergy ina nuclearreactionwith achange ofmassaccordingto theequationE = mc

2


240

Example 2Below is an equation involving the fission ofUranium-235 by a fast moving neutron.

energy3 10

9236

14156

10

23592 nKrBanU

Calculate the amount of energy released by an atomof Uranium 235.U-235 = 235.04 a.m.uKr-92 = 91.93 a.m.uBa-141 = 140.91 a.m.uNeutron = 1.01 a.m.u1 a.m.u = 1.66 x 10

-27kg

c = 3.0 x 108

m s-1

Example 3A possible fusion reaction is represented by thefollowing equation:

HHHH 11

31

21

21

Calculate the energy released in joules.H-2 = 2.014102 uH-3 = 3.016049 uH-1 = 1.007825 u1 a.m.u = 1.66 x 10

-27kg

c = 3.0 x 108

ms-1

A nuclearreactor

Electricity can be generated from the energy released by fission reactions.A nuclear power station consists of a nuclear reactor and a generator.

Describe the generation of electricity from nuclear fission


241

Uranium fuelrods :

Graphitemoderator:

Boron orcadmiumcontrol rod

Concreteshield:

Coolant:

Heatexchanger:

Turbines:

Coil andmagnet:

Process:

It produces tremendous amount of energy through nuclear fission.

The nuclei are split by neutrons in a controlled chain reaction, releasing a largeamount of energy. The energy released heats up the cold gas that passesthrough the reactor core.

Acts as a moderator to slow down the fast neutrons produced by the fission.Slower neutrons are more readily captured by the uranium nuclei.

The boron control rods absorb neutrons. It can control the rate of fissionreaction. When rods are lowered into the reactor core to absorb some of theneutrons, the rate of the fission reaction reduced.

Prevents leakage of radiation from the reactor core.

Take away the heat from the nuclear reactor. Substances with high specificheat capacity such as water and carbon dioxide are used.

Heat energy from the very hot gas is used to boil the water into steam

The turbines are rotated by the flow of steam under high pressure

The coils are rotated by the turbines. Electricity is generated byelectromagnetic induction.

Justify the useof nuclearfission in thegeneration ofelectricity

Advantages of using nuclear fission: Nuclear power costs about the same as coal, so it is not expensive It does not produce smoke or carbon dioxide. It does not contribute to the

greenhouse effect. It produces less waste than fossil fuels. It produces huge amounts of energy from small amounts of fuel. Nuclear power stations need less fuel than stations which use fossil fuels Vast reserves of nuclear fuel in the world. Safety procedures in the administration of nuclear reactors are very

advanced and safe Produces useful radioisotopes as by-products that can be used in industry,

medicine, agriculture and research.


242

Disadvantages of using nuclear fission The initial cost to design and build a nuclear power station is very high. There is always a risk of accidents. If a chain reaction goes out of control,

explosion or leakage or large amounts of radioactive substance mayhappen.

Used fuel rods are very hot and highly radioactive with very long half-lives. Expensive procedures are required to cool down the rods and store them. The hot water discharged from the nuclear power stations can cause

thermal pollution People who work in the nuclear power station and those living nearby may

be exposed to excessive radiation.

10.1 THE IMPORTANCE OF PROPER MANAGEMENT OF RADIOACTIVE SUBSTANCES

Sources ofbackgroundradiation

Our bodies are always exposed to the natural background radiation. The level of background radiation is very low and is not harmful to

humans.

Describe thenegative effectsof radioactivesubstances

Somatic effect

Genetic effect

When radioactive emissions strikes living cells, it can cause ionization tothe molecules of the cells. This may cause the cells to be killed, resultingin tissue damage.

At low doses of radiation, the damaged tissues can repair itself rapidly. High doses of radiation can cause burn effects known as radiation burns. The ionization effect of radiation can also cause genetic damage to the

molecules of the cells. This may lead to the formation of cancerous cellsand tumour development.

If the radioactive substances gets inside the body, the most harmfuleffects come from the alpha particles because they have the highestionization power.

If the radioactive source is outside the body, the greatest danger is fromgamma sources because gamma rays have the highest penetrating power.The alpha particles would not penetrate clothing and is highly unlikely toreach living cells in the body.

Somatic effect appears in the person exposed to radiation. Theseriousness of the damage depends on the dose of radiation received.Fatigue, nausea, hair loss, radiation burns, cataractsBlood disorder (leukemia), organ failure, death

Genetic effect affects the reproductive cells and can lead to defectiveoffspring in the future generations of the exposed person.Birth defects, congenital defects, premature death, chromosomeabnormalities, cancer in later life.


243

Describe safetyprecautionsneeded in thehandling ofradioactivesubstances

Radioactive substances must always be handled with the correct proceduresto prevent harmful effects to people and the environment. Read and follow the advice and instructions marked on radioactive

sources, equipment and work manuals. Gloves must be worn any time an unsealed source is being used or

whenever contamination is likely to occur. Laboratory coats, long pants, and closed-toe footwear should be worn. Eating, drinking, applying cosmetic or storing food is prohibited. All work surfaces and storage areas should be covered with absorbent

material to contain radioactive material contamination. When using radioactive liquids, plastic or metal trays (stainless steel

washes easily) should be utilized to contain potential spills. Radioactive material, especially liquids, should be kept in unbreakable

containers whenever possible. If glass is used, a secondary container isnecessary

Before eating or drinking, wash hands and forearms thoroughly. Stronger radioactive sources should be handled with robotic control

systems behind steel, concrete, lead or thick glass panels. Radiation badges containing photographic film should be worn to monitor

exposure to radiation. The film is regularly developed. The darkness ofthe film shows the level of exposure to radiation.

Describe themanagement ofradioactive waste

Low level waste:

Intermediate levelwaste:

In a nuclear reactor, a very large amount of energy is produced from a verysmall amount of fuel. However, much of the waste is radioactive andtherefore must be carefully managed as hazardous waste.Radioactive waste consists of a variety materials requiring different methodsof management to protect people and the environment.

Comprises 90% of the volume but only 1% of the radioactivity of allradioactive waste.

Generated from hospitals, laboratories and industry, as well as thenuclear fuel cycle.

Comprises paper, rags, tools, clothing, filters Contains small amounts of mostly short-lived radioactivity Buried in shallow landfill sites. Often compacted or incinerated (in a closed container) before disposal to

reduce its volume.

Makes up 7% of the volume and has 4% of the radioactivity of allradioactive waste.

Contains higher amounts of radioactivity and may require specialshielding

Comprises resins, chemical sludge, reactor components andcontaminated material from reactor decommissioning

Solidified in concrete or bitumen for disposal Short-lived waste (mainly from reactors) is buried. Long-lived waste (from reprocessing nuclear fuel) is disposed deep

underground

Consists of only 3% of the volume of all radioactive waste but it holds 95%of the radioactivity.

Mainly used fueled rods or liquid waste from fuel processing Contains highly-radioactive fission products and some heavy elements

with long-lived radioactivity.


244

Generates large amount of heat and requires cooling, as well as specialshielding during handling and transport.

Vitrified by incorporating it into borosilicate glass which is sealed insidestainless steel containers for eventual disposal deep underground.

TUTORIAL10.4

1 A Uranium-235 nucleus will split when itcapturesA an alpha particleB a gamma rayC a neutronD a proton

2 Which of the following nuclear reactionsis an example of fusion?

A C146 → N14

7 + e01- + energy

B H21 + H2

1 → He32 + e0

1- + energy

C Na2111 → Mg21

12 + β + energy

D Ra22688 → Rn222

86 + α + energy

3 The diagram shows the start of a chainreaction.

Which nuclear reaction is taking place?A Fission of hydrogenB Fusion of hydrogenC Fission of uraniumD Fusion of uranium

4 It is possible for a chain reaction tooccur in nuclear fission becauseA new neutrons are producedB two fission fragments are producedC a large amount of energy is releasedD fission does not require a very high

temperature

5 In a nuclear reactor , the neutronsproduced are slowed down byA Uranium rodB Graphite coreC Boron control rod

6 What energy changes take place in anuclear power station?A Heat energy→ Mechanical energy

→ Nuclear energy B Nuclear energy→ Heat energy

→ Electrical energy C Heat energy→ Nuclear energy

→ Electrical energy D Mechanical energy→ Heat energy

→ Electrical energy

7 Which of the following is not true abouta nuclear reactor?

Component

Function

A Controlrod

To control the rate offission reaction.

B Coolant To take away heat fromthe nuclear reactor

C Graphitecore

To slow down the fastneutrons produced bythe fission.

D Concreteshield

To prevent theradioactive radiationsfrom atmosphereentering into thenuclear reactor

8 Which of the following nuclear reactionsis an example of fission?

A H21 + H2

1 → He42 + energy

B N147 + neutron → N15

7 + energy

C Pu21494 → U237

92 + α + energy

D U23992 → Sr95

38 + Xe14154 +

3 neutrons + energy


246

9 In the sun, energy is released whenhydrogen nuclei collide and formheavier nuclei. This process is calledA IonisationB DiffusionC FissionD Fusion

11 What happen when two nuclei of

deuterium ( H21 ) fuse together to form a

nucleus helium ( He42 ) ?

A Mass and energy are both createdB Energy and mass are both lostC Mass is converted into energyD Energy is converted into mass

12 Which of the following is made by usingthe principle of nuclear fusion.

A Atom bombB Hydrogen bombC Nuclear reactor

13 Which of the following is not thesimilarity between nuclear fission andnuclear fusion?A Both of the nuclear reactions

experience mass defectB Both of the nuclear reactions

produced a large amount of energyC Both of the nuclear reactions

produced new nucleiD Both of the nuclear reactions

require very high temperature

14 A nuclear reaction is given by theequation

X → Y + Z

Which of the following is correct?A The nucleon number of X > The

nucleon number of Y + nucleonnumber of Z

B The proton number of X > Theproton number of Y + protonnumber of Z

C The atomic mass of X > The atomicmass of Y + the atomic mass of Z

15. The mass defect in a nuclear reaction is0.05 u. What is the released?

[ Speed of light = 3.0 x 10 8 ms-1

,

A 2.55 x 10 -21J B 5.10 x 10 -19 J

C 3.83 x 10 -13J D 7.65 x 10 -13 J

E 8.97 x 10 -13 J

16. In the fission reaction for an atom ofuranium-235, the energy produced is 2.9 x10

-11J. What is the total loss of mass in

the reaction? (2007)A. 3.22 x 10

-28kg

B. 9.67 x 10-20

kgC. 2.61 x 10

6kg

D. 1.03 x 1019

kg

17. A nuclear reaction is represented by thefollowing equation:

U23592 + n1

0 → Cs14155 + Rb93

37 + X n10 +

energy

The information about the equation isshown as follow:

Mass of U23592 = 235.04392 u

Mass of n10 = 1.00867 u

Mass of Cs14155 = 140.91963 u

Mass of Rb9337 = 92.92157 u

1 u = 11.7 x 10 -27 kg

Speed of light = 3.0 x 10 8 ms-1

(a) What is the value of X?

________________________________

(b)Name the nuclear reaction involved.

________________________________

(c) What is the meaning of the nuclearreaction in (b)?

_______________________________

_______________________________

(d) State one application of the nuclearreaction in (b)

______________________________


247

(e) Calculate

(i) the energy released .

(ii) the power generated in 5 µs.

18.Diagram below shows the structure of thenuclear reactor which is used to generateelectrical energy.

(a) Name the parts labeled X, Y and Z.

(i) X : _____________________________

(ii) Y : _____________________________

(iii) Z : _____________________________

(b) Name the reaction that takes place in thenuclear reactor.

___________________________________

(c) Neutrons with low kinetic energy areneeded for producing effective nuclearreactions. How are neutrons with lowkinetic energy produced?

___________________________________

___________________________________

(d) The neutrons which produced nuclearreaction will explode if the reaction is notcontrolled. How is the chain reactioncontrolled?

(e) Why does the nuclear reactor commonlybuild nearer to a river or a huge watersource?

___________________________________

19.Figure 1 and 2 represent the radioactivedecay of radium-226 and carbon-14respectively.

(f) (i) Why does theparent nuclide decay?

________________________________

(ii) Compare the total masses in a.m.ubefore and after the decay process.

________________________________

(iii) Explain the reason for theobservation in (a)(ii).

(iv) Write an equation to show therelationship between mass defect, m,speed of light, c and energy, E.


248

(v) State the relationship between themass defect and the energyreleased.

______________________________

(g) The half-lives of radium-226 andcarbon-14 are 1 600 years and 5 600years respectively.(i) What is meant by half-life?

_____________________________

_____________________________

(ii) Which radioactive material willdecay a faster rate? Explain youranswer.

______________________________

______________________________

SPM 2004 (essay)20. Table (a) shows an equation of a reaction

and total atomic mass before and after anuclear fission.

Nuclear fissionBefore

reactionAfter reaction

Equation239

Pu +1n

94 0

145Ba +

93Sr +

56 38

21n +

Energy0

Totalatomicmass

240.06082 u 239.85830 u

Table (a)

Table (b) shows an equation of a reactionand total atomic mass before and after anuclear fusion.

Nuclear fusionBefore

reactionAfter reaction

Equation2

H +3H

1 1

4He +

1n +

2 0

Energy

Totalatomicmass

5.03013 u 5.01043 u

Table (b)

(a)(i) What is meant by a nuclear fission ?

(ii) Using only the information given inTable(a) and (b), compare nuclearfission and nuclear fusion. Hencestate the relationship between massand energy involved.

(b) Nuclear fission produces a chainreaction. Describe how the chainreaction happens in a nuclear fission ofan atom of uranium.

10 radioactivity

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