1 chapter 9 nuclear radiation 9.1 natural radioactivity copyright © 2009 by pearson education, inc

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Chapter 9 Nuclear Radiation

9.1 Natural Radioactivity

Copyright © 2009 by Pearson Education, Inc.

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Radioactive Isotopes

A radioactive isotope • has an unstable nucleus.• emits radiation to become more stable.• can be one or more of the isotopes of an element


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Nuclear Radiation

Nuclear radiation • is the radiation emitted by an unstable atom.• takes the form of alpha particles, neutrons, beta

particles, positrons, or gamma rays.


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Types of Radiation

Alpha () particle is two protons and two neutrons.

Beta () particle is a high-energy electron. 0e -1

Positron (+) is a positive electron. 0e +1

Gamma ray is high-energy radiation released from a nucleus.

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Radiation Protection

Radiation protection requires • paper and clothing for alpha particles.• a lab coat or gloves for beta particles.• a lead shield or a thick concrete wall for

gamma rays.• limiting the amount of time spent near

a radioactive source.• increasing the distance from the source.


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Shielding for Radiation Protection

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9.2Nuclear Reactions


Changes in Nuclear Particles Due to Radiation

When radiation occurs,• particles are emitted from the nucleus.• mass number may change.• atomic number may change.

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Summary of Types of Radiation


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Producing Radioactive Isotopes

Radioactive isotopes are produced • when a stable nucleus is converted to a radioactive

nucleus by bombarding it with a small particle.• in a process called transmutation.


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9.3 Radiation Measurement

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Radiation Measurement

A Geiger counter • detects beta and gamma radiation.• uses ions produced by radiation to create an

electrical current.


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Radiation Units

Units of radiation include• Curie

- measures activity as the number of atoms that decay in 1 second.

• rad (radiation absorbed dose) - measures the radiation absorbed by the

tissues of the body.• rem (radiation equivalent)

- measures the biological damage caused by different types of radiation.

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Units of Radiation Measurement

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Exposure to Radiation

Exposure to radiation occurs from

• naturally occurring radioisotopes.

• medical and dental procedures.

• air travel, radon, and smoking cigarettes.


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9.4 Half-Life of a Radioisotope9.5 Medical Applications Using

Radioactivity

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Half-Life

The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one half of the original value.


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Decay Curve

A decay curve shows the decay of radioactive atoms and the remaining radioactive sample.


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Half-Lives of Some Radioisotopes

Radioisotopes• that are naturally occurring tend to have long half-lives.• used in nuclear medicine have short half-lives.


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Medical Applications

Radioisotopes with short half-lives are used in nuclear medicine because

• they have the same chemistry in the body as the nonradioactive atoms.

• in the organs of the body, they give off radiation that exposes a photographic plate (scan), giving an image of an organ. Thyroid scan


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Some Radioisotopes Used in Nuclear Medicine


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9.6 Nuclear Fission and Fusion


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In nuclear fission,

• a large nucleus is bombarded with a small particle.

• the nucleus splits into smaller nuclei and several neutrons.

• large amounts of energy are released.

Nuclear Fission

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When a neutron bombards 235U,

• an unstable nucleus of 236U undergoes fission (splits).• smaller nuclei are produced, such as Kr-91 and Ba-142.• neutrons are released to bombard more 235U.

1n + 235U 236U 91Kr + 142Ba + 3 1n +

0 92 92 36 56 0

Nuclear Fission

Energy

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Nuclear Fission Diagram

1n + 235U 236U 91Kr + 142Ba + 3 1n + energy 0 92 92 36 56 0


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Chain Reaction

A chain reaction occurs

• when a critical mass of uranium undergoes fission.

• releasing a large amount of heat and energy that produces an atomic explosion.


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Nuclear Power Plants

In nuclear power plants, • fission is used to produce energy.• control rods in the reactor absorb neutrons to

slow and control the chain reactions of fission.


Strontium - 90

90Sr is a product of nuclear fission. It is present in significant amount in spent nuclear fuel and in radioactive waste from nuclear reactors and in nuclear fallout from nuclear tests.

For thermal neutron fission as in today's nuclear power plants, the fission product yield from U-235 is 5.8%, from U-233 6.8%, but from Pu-239 only 2.1%.

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Strontium - 90

Together with caesium isotopes 134Cs, 137Cs, and iodine isotope 131I it was among the most important isotopes regarding health impacts after the Chernobyl disaster.

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Strontium -90

Strontium-90 is a "bone seeker" that exhibits biochemical behavior similar to calcium, the next lighter Group 2 element. After entering the organism, most often by ingestion with contaminated food or water, about 70-80% of the dose gets excreted.

Virtually all remaining strontium-90 is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues.

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Strontium - 90

Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia. Exposure to 90Sr can be tested by a bioassay, most commonly by urinalysis.

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Iodine -131

131I is a fission product with a yield of 2.878% from uranium-235,[5] and can be released in nuclear weapons tests and nuclear accidents.

However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel, unlike iodine-129 whose half-life is nearly a billion times that of I-131.

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Iodine - 131

131I decays with a half-life of 8.02 days with beta and gamma emissions. This nuclide of iodine atom has 78 neutrons in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I transforms into 131Xe

The primary emissions of 131I decay are 364 keV gamma rays (81% abundance) and beta particles with a maximal energy of 606 keV (89% abundance).

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Iodine -131

The beta particles, due to their high mean energy (190 keV; 606 kev is the maximum, but a typical beta-decay spectrum is present) have a tissue penetration of 0.6 to 2 mm.

Due to its mode of beta decay, iodine-131 is notable for causing mutation and death in cells which it penetrates, and other cells up to several millimeters away.

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1 chapter 9 nuclear radiation 9.1 natural radioactivity copyright © 2009 by pearson education, inc

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