Chapter 9 Nuclear Radiation

9.1Natural Radioactivity

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Stable and Radioactive Isotopes

A radioactive isotope • has an unstable nucleus• emits radiation to become more stable, changing the

composition of the nucleus• is identified by the mass number of the isotope

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Nuclear Radiation

Nuclear radiation is the radiation emitted by an unstable atom and 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.

Positron (+) is a positive electron.

Gamma rays are the high-energy radiation released from a nucleus when it decays.

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He42

e01

00

e01

Learning Check

Give the name and symbol for the following types of radiation.A. alpha radiationB. radiation with a mass number of 0 and atomic number

of +1C. radiation that represents high-energy radiation

released from the nucleus

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Solution

Give the name and symbol for the following types of radiation.A. alpha radiation

B. radiation with a mass number of 0 and atomic number of +1

C. radiation that represents high-energy radiation released from the nucleus

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He42

e01

00

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 distance from the source

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Shielding for Radiation Protection

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Learning Check

What type of radiation will be blocked by

A. lead shieldB. paper, clothing

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Solution

What type of radiation will be blocked by

A. lead shield gamma radiationB. paper, clothing alpha radiation

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Chapter 9 Nuclear Radiation

9.2Nuclear Equations

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Balancing Nuclear Equations

In a balanced nuclear equation, particles are emitted from the nucleus, and

• the mass number and atomic number may change• the sum of the mass numbers and the sum of the atomic

numbers are equal for the reactants and the products Mass number sum: 251 = 251

251Cf 247Cm + 4He 98 96 2

Atomic number sum: 98 = 98

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Guide to Balancing Nuclear Equations

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Alpha Decay

When a radioactive nucleus emits an alpha particle, a new nucleus forms with a mass number that is decreased by 4 and an atomic number that is decreased by 2.

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Equation for Alpha Emission

Write an equation for the alpha decay of Rn-222.

Step 1 Write the incomplete nuclear equation.

Step 2 Determine the missing mass number. 222 – 4 = 218

Step 3 Determine the missing atomic number.86 – 2 = 84

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He42

HeRn 42 ? 222

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Equation for Alpha Emission

Write an equation for the alpha decay of Rn-222.

Step 4 Determine the symbol of the new nucleus.

84 = Po

Step 5 Complete the nuclear equation.

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HePoRn 42 218

84 22286

Beta Emission

A beta particle is an electron emitted from the nucleus when a neutron in the nucleus breaks down, increasing the atomic number by 1.

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Equation for Beta Emission

Write an equation for the decay of 42K, a beta emitter.Step 1 Write the incomplete nuclear equation.

Step 2 Determine the missing mass number. 42 – 0 = 42

Step 3 Determine the missing atomic number.19 (1) = 20

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eK 01 ? 42

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Equation for Beta Emission

Write an equation for the decay of 42K, a beta emitter.Step 4 Determine the symbol of the new nucleus.

20 = Ca

Step 5 Complete the nuclear equation.

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eCaK 01 42

20 4219

Learning Check

Write the nuclear equation for the beta decay of 60Co.

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Solution

Write the nuclear equation for the beta decay of 60Co.Step 1 Write the incomplete nuclear equation.

Step 2 Determine the missing mass number.

60 – 0 = 60Step 3 Determine the missing atomic number.

27 (1) = 28

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eCo 01 ? 60

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Solution

Write the nuclear equation for the beta decay of 60Co.

Step 4 Determine the symbol of the new nucleus.

28 = Ni

Step 5 Complete the nuclear equation.

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eNiCo 01 60

28 6027

Positron Emission

In positron emission,• a proton is converted to a neutron and a positron.

• the mass number of the new nucleus is the same, but the atomic number decreases by 1.

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enp 01 1

0 11

e01

eCrMn 01 49

24 4925

Gamma Radiation

In gamma radiation,• energy is emitted from an unstable nucleus, indicated by

m following the mass number• the mass number and the atomic number of the new

nucleus are the same

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00

00 99

43 9943 TcTcm

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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When nonradioactive B-10 is bombarded by an alpha particle, the products are radioactive N-13 and a neutron.

Learning Check

What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle?

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HenTc 42 ? 1

0 9827

Solution

What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle?Step 1 Write the incomplete nuclear equation.

Step 2 Determine the missing mass number. 98 + 1 4 = 95

Step 3 Determine the missing atomic number.27 2 = 25

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HenTc 42 ? 1

0 9827

Solution

What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle?Step 4 Determine the symbol of the new nucleus.

25 = Mn

Step 5 Complete the nuclear equation.

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HeMnnTc 42 95

25 10 98

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Chapter 9 Nuclear Radiation

9.3Radiation Measurement

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Geiger Counter

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

current

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Units for Measuring Radiation

Units for measuring radiation activity 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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Measuring Radiation Activity

Often the measurement for an equivalent dose is in millirems (mrem). One rem is equal to 1000 mrem. The SI unit is the sievert (Sv). One sievert is equal to 100 rem.

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Radiation Exposure

Exposure to radiation occurs from• naturally occurring

radioisotopes• medical and dental procedures• air travel, radon, and smoking

cigarettes• cosmic rays

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Radiation Sickness

LD50

• is the amount of radiation to the whole body that is the lethal dose for one-half the population

• varies for different life-forms, as Table 9.6 shows

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Learning Check

A typical intravenous dose of I-125 for a thyroid diagnostic test is 100 Ci. What is this dosage in megabecquerels (MBq) (3.7 1010 Bq = 1 Ci)?

A. 3.7 MBqB. 3.7 106 MBqC. 2.7 102 MBq

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Solution

A typical intravenous dose of I-125 for a thyroid diagnostic test is 100 Ci. What is this dosage in megabecquerels (MBq) (3.7 1010 Bq = 1 Ci)?

100 Ci 1 Ci 3.7 1010 Bq 1 MBq x 1 x 106 Ci 1 Ci 1 106 Bq

= 3.7 MBq The answer is A.

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Chapter 9 Nuclear Radiation

9.4Half-Life of a Radioisotope

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Half-Life and Decay Curves

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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The decay curve for I-131 shows that one-half the sample decays every 8 days.

Half-Lives of Some Radioisotopes

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Guide to Using Half-Lives

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Half-Life Calculations

The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years?Step 1 State the given and needed quantities.

Given: 36 mg, 152.4 years, half-life of 38.1 yearsNeeded: mg Sr-90 remaining

Step 2 Write a plan to calculate unknown quantity. Half-life

152.4 years number of half-lives Number of half-lives

36 mg Sr-90 mg Sr-90 remaining

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Half-Life Calculations

The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years?

Step 3 Write the half-life equality and conversion factors. 1 half-life = 38.1 years

38.1 years and 1 half-life 1 half-life 38.1 years

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Half-Life Calculations

The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years?

Step 4 Set up the problem to calculate amount of active radioisotope.

Number of half-lives4 years x 1 half-life = 4 half-lives

38.1 years 1 half-life 2 half-lives 3 half-lives 4 half-lives

36 mg 18 mg 9 mg 4.5 mg 2.3 mg Sr-90

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Learning Check

Carbon-14 was used to determine the age of the Dead Sea Scrolls. If the Dead Sea Scrolls were determined to be 2000 years old and the half-life of carbon-14 is 5730 years, what fraction of this half-life has passed?

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Solution

Carbon-14 was used to determine the age of the Dead Sea Scrolls. If the Dead Sea Scrolls were determined to be 2000 years old and the half-life of carbon-14 is 5730 years, what fraction of this half-life has passed?

2000 years x 1 half-life = 0.35 half-life 5730 years

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Learning Check

The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours?

A. 32 mgB. 16 mgC. 8 mg

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Solution

The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours?Step 1 State the given and needed quantities.

Given: 64 mg, 26 hours, half-life of 13 hoursNeeded: mg I-123 remaining

Step 2 Write a plan to calculate unknown quantity. Half-life

26 hours number of half-lives Number of half-lives

64 mg I-123 mg I-123 remaining

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Solution

The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours?

Step 3 Write the half-life equality and conversion factors. 1 half-life = 13 hours

13 hours and 1 half-life 1 half-life 13 hours

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Solution

The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours?

Step 4 Set up the problem to calculate amount of active radioisotope.

Number of half-lives26 hours x 1 half-life = 2 half-lives

13 hours

1 half-life 2 half-lives64 mg 32 mg 16 mg I-123

The answer is B, 16 mg of I-123 remain.50

Chapter 9 Nuclear Radiation

9.5 Medical Applications

Using Radioactivity

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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

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Medical Applications of Radioisotopes

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Scans with Radioisotopes

After a radioisotope is ingested by the patient,• the radiologist determines the level and location of

the radioactivity emitted by the radioisotope• the scanner moves slowly over the organ where the

radioisotope is absorbed• the gamma rays emitted from the radioisotope can be

used to expose a photographic plate, giving a scan of the organ

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Scans with Radioisotopes

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(a) A scanner is used to detect radiation from a radioisotope that has accumulated in an organ. (b) A scan of the thyroid shows the accumulation of radioactive iodine-131 in the thyroid.

Positron Emission Tomography (PET)

Positron emitters with short half-lives • can be used to study brain function, metabolism, and

blood flow• include carbon-11, oxygen-15, nitrogen-13, and fluorine-18

• combine with electrons after emission to produce gamma rays, which are then detected by computers, creating a 3-D image of the organ

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8189 O F

Positron Emission Tomography (PET)

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These PET scans of the brain show a normal brain on the left and a brain affected by Alzheimer’s disease on the right.

Computed Tomography (CT)

A computer monitors the absorption of 30 000 X-ray beams directed at the brain in successive layers.

Differences in absorption based on tissue densities and fluids provide images of the brain.

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Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging• is an imaging technique that does not involve

X-ray radiation• is the least invasive imaging method available• is based on absorption of energy when protons in

hydrogen atoms are excited by a strong magnetic field• works because the energy absorbed is converted to color

images of the body

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Magnetic Resonance Imaging

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An MRI scan of the heart and lungs, with the left ventricle shown in red.

Learning Check

Which of the following radioisotopes are most likely to be used in nuclear medicine?

A. 40K half-life 1.3 x 109 years

B. 42K half-life 12 hours

C. 131I half-life 8 days

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Solution

Which of the following radioisotopes are most likely to be used in nuclear medicine?

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

A. 40K half-life 1.3 109 years Not likely: half-life is too long.

B. 42K half-life 12 hours Short half-life, likely used.

C. 131I half-life 8 days Short half-life, likely used.

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Chapter 9 Nuclear Radiation

9.6 Nuclear Fission and Fusion

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Nuclear Fission

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

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Nuclear Fission

When a neutron bombards 235U,

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

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Nuclear Fission Diagram

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

Nuclear Fission Chain Reaction

In a nuclear chain reaction, the fission of each U-235 atom produces three neutrons that cause the nuclear fission of more and more uranium-235 atoms.

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Energy and Nuclear Fission

The total mass of the products in this reaction is slightly less than the mass of the starting materials. The missing mass has been converted into energy, consistent with the famous equation derived by Albert Einstein, E = mc2.

E is the energy released, m is the mass lost, and c is the speed of light, 3.0 108 m/s. Using this equation, a small amount of mass is multiplied by the speed of light squared, resulting in a large amount of energy.

Fission of 1 g U-235 produces same energy as 3 tons of coal.

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Learning Check

Supply the missing atomic symbol to complete the equation

for the following nuclear fission reaction.

1n + 235U 137Te + ?X + 2 1n + energy 0 92 52 ? 0

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Solution

Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.

1n + 235U 137Te + 97Zr + 2 1n + energy0 92 52 40 0

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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

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Nuclear Fusion

Fusion• occurs at extremely high temperatures (100 000 000 C)• combines small nuclei into larger nuclei• releases large amounts of energy• occurs continuously in the sun and stars

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Hydrogen atoms combine in a fusion reactor at very high temperatures.

Learning Check

Indicate whether each of the following describes nuclear fission or nuclear fusion.

___ A. A nucleus splits.___ B. Large amounts of energy are released.___ C. Small nuclei form larger nuclei.___ D. Hydrogen nuclei react.___ E. Several neutrons are released.

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Solution

Indicate whether each of the following is nuclear fission or nuclear fusion.nuclear fission A. A nucleus splits.nuclear fission and fusion B. Large amounts of energy

are released.nuclear fusion C. Small nuclei form larger nuclei.nuclear fusion D. Hydrogen nuclei react.nuclear fission E. Several neutrons are released.

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Nuclear Radiation – Concept Map

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