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25.1 Nuclear Radiation >25.1 Nuclear Radiation >

1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Chapter 25Nuclear Chemistry

25.1 Nuclear Radiation

25.2 Nuclear Transformations25.3 Fission and Fusion25.4 Radiation in Your Life



What makes some types of radiation more dangerous than other types?

CHEMISTRY & YOUCHEMISTRY & YOU

Lengthy or frequent exposure to X-rays can damage cells in your body.



RadioactivityRadioactivity

Radioactivity

How do nuclear reactions differ from chemical reactions?




In 1896, the French chemist Antoine Becquerel made an accidental discovery.

• He was studying the ability of uranium salts that had been exposed to sunlight to fog photographic film plates.




In 1896, the French chemist Antoine Becquerel made an accidental discovery.

• He was studying the ability of uranium salts that had been exposed to sunlight to fog photographic film plates.

• During bad weather, when Becquerel could not expose a sample to sunlight, he left the sample on top of the photographic plate.

• When he developed the plate, he discovered that the uranium salt still fogged the film.




Two of Becquerel’s associates were Marie and Pierre Curie.

• The Curies were able to show that rays emitted by uranium atoms caused the film to fog.

• Marie Curie and her husband Pierre shared the 1903 Nobel Prize in physics with Becquerel for their pioneering work on radioactivity.




Marie Curie used the term radioactivity to refer to the spontaneous emission of rays or particles from certain elements, such as uranium.




Marie Curie used the term radioactivity to refer to the spontaneous emission of rays or particles from certain elements, such as uranium.• The rays and particles emitted from a

radioactive source are called nuclear radiation.




Radioactivity, which is also called radioactive decay, is an example of a nuclear reaction.• Nuclear reactions begin with unstable

isotopes, or radioisotopes.






• Atoms of these isotopes become more stable when changes occur in their nuclei.






• Atoms of these isotopes become more stable when changes occur in their nuclei.

• The changes are always accompanied by the emission of large amounts of energy.




Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Also, nuclear reactions of a given radioisotope cannot be slowed down, sped up, or stopped.




Radioactive decay is a spontaneous process that does not require an input of energy.




Radioactive decay is a spontaneous process that does not require an input of energy.• If the product of a nuclear reaction is

unstable, it will decay too.






• The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element.






• The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element.

• These stable isotopes are not radioactive.



Why do unstable isotopes undergo nuclear reactions?



Why do unstable isotopes undergo nuclear reactions?

Unstable isotopes undergo nuclear reactions so that they may be changed, or transformed, into stable isotopes.



Types of RadiationTypes of Radiation

Types of Radiation

What are three types of nuclear radiation?




Radiation is emitted during radioactive decay.

Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.



Characteristics of Some Types of Radiation

Type Consists of Symbol ChargeMass (amu)

Common source

Penetrating power

Alpha radiation

Alpha particles (helium nuclei)

, 2+ 4Radium-226

Low (0.05 mm body tissue)

Beta radiation

Beta particles (electrons)

, 1– 1/1837Carbon-14

Moderate (4 mm body tissue)

Gamma radiation

High-energy electromagnetic radiation

0 0 Cobalt-60Very high (penetrates body easily)

He42

e0–1

Interpret DataInterpret Data




Alpha Radiation

Some radioactive sources emit helium nuclei, which are also called alpha particles.




Alpha Radiation


• Each alpha particle contains two protons and two neutrons and has a double positive charge.




Alpha Radiation


• Each alpha particle contains two protons and two neutrons and has a double positive charge.

• An alpha particle is written He or .42

– The electric charge is usually omitted.




Alpha RadiationThe radioisotope uranium-238 emits alpha radiation and is transformed into another radioisotope, thorium-234.

U23892

Uranium-238

Th +23490

Thorium-234

He ( emission)42

Alpha particle

Radioactivedecay




Alpha Radiation

When an atom loses an alpha particle, the atomic number of the product is lowered by two and its mass number is lowered by four.

• In a balanced nuclear equation, the sum of the mass numbers (superscripts) on the right must equal the sum on the left.

• The same is true for the atomic numbers (subscripts).

U23892 Th +234

90 He42→




Alpha Radiation

Because of their large mass and charge, alpha particles do not travel very far and are not very penetrating.

• A sheet of paper or the surface of your skin can stop them.

• But radioisotopes that emit alpha particles can cause harm when ingested.– Once inside the body, the particles don’t have

to travel far to penetrate soft tissue.




Beta Radiation

An electron resulting from the breaking apart of a neutron in an atom is called a beta particle.• The neutron breaks apart into a proton, which

remains in the nucleus, and a fast-moving electron, which is released.

n10

Neutron

p +11

Proton

e 0–1

Electron(beta particle)

→




Beta Radiation

The symbol for the electron has a subscript of –1 and a superscript of 0.

• The –1 represents the charge on the electron.

• The 0 represents the extremely small mass of the electron compared to the mass of a proton.

n10

Neutron

p +11

Proton

e 0–1

Electron(beta particle)

→




Beta RadiationCarbon-14 emits a beta particle as it decays and forms nitrogen-14.

• The nitrogen-14 atom has the same mass number as carbon-14, but its atomic number has increased by 1.

• It contains an additional proton and one fewer neutron.

C146

Carbon-14 (radioactive)

N +147

Nitrogen-14 (stable)

e ( emission)0–1

Beta particle

→




Beta Radiation

A beta particle has less charge than an alpha particle and much less mass than an alpha particle.

• Thus, beta particles are more penetrating than alpha particles.

– Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood.




Beta RadiationBecause of their opposite charges, alpha and beta radiation can be separated by an electric field.

• Alpha particles move toward the negative plate.

• Beta particles move toward the positive plate.

• Gamma rays are not deflected.




Gamma RadiationA high-energy photon emitted by a radioisotope is called a gamma ray.• The high-energy photons are a form of

electromagnetic radiation.• Nuclei often emit gamma rays along with alpha or beta

particles during radioactive decay.

Ra +22688

Radium-226

Th23090

Thorium-230

He + 42

Alpha particle

Gamma ray

→

Pa +23491

Protactinium-234

Th23490

Thorium-234

e + 0–1

Beta particle

Gamma ray

→




Gamma rays have no mass and no electrical charge.

• Emission of gamma radiation does not alter the atomic number or mass number of an atom.

Gamma Radiation




Because gamma rays are extremely penetrating, they can be very dangerous.• Gamma rays pass easily through paper, wood, and the

human body.

• They can be stopped, although not completely, by several meters of concrete or several centimeters of lead.

Gamma Radiation



Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation?




Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation?


The wavelength and energy of electromagnetic radiation determine its relative penetrating power. Gamma rays have a shorter wavelength and higher energy than X-rays or visible light.



Which process involves a radioactive nucleus releasing a high-speed electron?

A. oxidation

B. alpha emission

C. beta emission

D. gamma radiation



A. oxidation

B. alpha emission

C. beta emission

D. gamma radiation

Which process involves a radioactive nucleus releasing a high-speed electron?



Key ConceptsKey Concepts

Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Also, nuclear reactions of a given radioisotope cannot be slowed down, sped up, or stopped.

Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.



Glossary TermsGlossary Terms

• radioactivity: the process by which nuclei emit particles and rays

• nuclear radiation: the penetrating rays and particles emitted by a radioactive source

• radioisotope: an isotope that has an unstable nucleus and undergoes radioactive decay



Glossary TermsGlossary Terms

• alpha particle: a positively charged particle emitted from certain radioactive nuclei; it consists of two protons and two neutrons and is identical to the nucleus of a helium atom

• beta particle: an electron resulting from the breaking apart of neutrons in an atom

• gamma ray: a high-energy photon emitted by a radioisotope



Electrons and the Structure of Atoms

• Unstable atomic nuclei decay by emitting alpha or beta particles.

• Often gamma rays are emitted too.

BIG IDEABIG IDEA



END OF 25.1END OF 25.1

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