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Nuclear Radiation

Natural Radioactivity

A person working with radioisotopes wears protective clothing and gloves and stands behind a shield.

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Radioactive Isotopes

A radioactive isotope • has an unstable nucleus• emits radiation to become more stable• can be one or more isotopes of an element• is written with a mass number and an atomic

number• includes the mass number in its name

Example: iodine-131

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Examples of Radioactive Isotopes

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Learning Check

Thallium-201 is used for heart scans to determine cardiac function.

A. How many protons are in thallium-201?

B. How many neutrons are in thallium-201?

C. What is the atomic symbol of thallium-201?

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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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Alpha Particle

An alpha () particle has• a helium nucleus• 2 protons and 2 neutrons• a mass number of 4• a charge of 2+• a low energy compared to

other radiation particles

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Beta ParticleA beta () particle • is a high-energy electron• has a mass number of 0• has a charge of 1-• forms in an unstable nucleus when a neutron

changes into a proton and an electron

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PositronA positron ( +)• has a mass number of 0• has a charge of 1+• forms in an unstable nucleus when a proton

changes into a neutron and a positron

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Gamma () RayA gamma () ray • is high-energy radiation• has a mass number of 0• has a charge of 0• is emitted from an unstable nucleus to give a

more stable, lower energy nucleus

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Summary of Common Forms of Nuclear Radiation

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Learning Check

Give the mass number and charge of each type of

radiation.

1. alpha particle

2. positron

3. beta particle

4. neutron

5. gamma ray

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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

Radiation Protection

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Radiation and Shielding Required

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Radiation Protection

Different types of shielding are needed for different radiation particles.

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Learning Check

Indicate the type of radiation (alpha, beta, and/or gamma) protection for each type of shielding.

1) heavy clothing

2) paper

3) lead

4) lab coat

5) thick concrete

A person working with radioisotopes wears protective clothing and gloves and stands behind a shield.

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Nuclear Radiation

Nuclear Equations

A radon gas detector is used to determine radon levels in buildings with inadequate ventilation.

Radioactive Decay

In radioactive decay, • a nucleus spontaneously emits radiation• a nuclear equation is written for the radioactive

nucleus, the new nucleus, and the radiation emitted

Radioactive nucleus

new nucleus + radiation (, , , +)

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In a nuclear equation, the type of radiation emitted causes

• changes in the mass numbers

• changes in the atomic numbers for the nuclei of the unstable and stable nuclei

Nuclear Equations

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In a balanced nuclear equation, • the sum of the atomic numbers for the nuclei

of the reactant and the products must be equal

Mass Numbers Total = 238 = 238

Total = 92 = 92 Atomic Numbers

Balancing Nuclear Equations

238 234 492 90 2U Th + He

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Guide to Completing a Nuclear Equation

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Alpha Decay

In alpha decay, a

radioactive nucleus emits

an alpha particle to form a

new nucleus that has • a mass number 4 less

than that of the initial nucleus

• an atomic number that has decreased by 2 from that of the initial nucleus

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Example of Writing an Equation for Alpha Decay

Write an equation for the alpha decay ofSTEP 1 Write the incomplete nuclear equation.

STEP 2 Determine the missing mass number.

222 = ? + 4

222 – 4 = 218

218 = ? (mass number of new nucleus)

22286 Rn

222 486 2Rn ? + He

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Equation for Alpha Decay (continued)

STEP 3 Determine the missing atomic number. 86 = ? + 2

86 – 2 = ? 84 = ? (atomic number of new nucleus

STEP 4 Determine the symbol of the new nucleus.

Symbol of element 84 = Po

STEP 5 Complete the nuclear equation.

222 218 486 84 2Rn Po + He

21884 Po

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Beta Decay

Beta decay occurs when• an electron (beta

particle) is emitted from the nucleus

• a neutron in the nucleus breaks down

1 0 10 -1 1 + H n e

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Write an equation for the beta decay of potassium-42.STEP 1 Write the incomplete nuclear equation.

STEP 2 Determine the missing mass number. 42 = ? + 0

42 0 = 42 = ? (mass number of new nucleus)

STEP 3 Determine the missing atomic number. 19 = ? 1

19 + 1 = ? 20 = ? (atomic number of new nucleus)

Writing an Equation for a Beta Emitter

42 0 19 -1K ? + e

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STEP 4 Determine the symbol of the new nucleus.

Symbol of element 20 = Ca

STEP 5 Complete the nuclear equation.

Writing an Equation for a Beta Emitter (continued)

42 20Ca

42 42 0 19 20 -1K Ca + e

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Write the nuclear equation for the beta decay of Xe-133.

Learning Check

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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

Positron Emission

1 1 01 0 +1H n e

49 49 0 25 24 +1Mn Cr + e

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Write the nuclear equation for the positron emission by Rb-82.

Learning Check

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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

Gamma ( ) Radiation

99m 99 0 43 43 0Tc Tc +

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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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What radioactive isotope is produced when a neutron bombards cobalt-59 and an alpha particle is emitted?

Learning Check

59 1 427 0 2Co + ? + Hen

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Nuclear Radiation

Radiation Measurement

A radiation technician uses a Geiger Counter to check radiation levels.

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Radiation Detection

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

an electrical current

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Radiation Measurement

Radiation units of activity include• curie (Ci) SI unit = becquerel (Bq)

number of atoms that decay in one second 1 Ci = 3.7 x 1010 disintegrations/s

1 Ci = 3.7 x 1010 Bq• rad (radiation absorbed dose) SI unit = gray(Gy) radiation absorbed by the tissues of the body

1 Gy = 100 rad• rem (radiation equivalent) SI unit = sievert (Sv) biological damage caused by different types of radiation = absorbed dose (rad) x factor 1 Sv = 100 rem

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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

Radiation Sickness

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Radiation sickness• depends on the dose of radiation received at

one time• is not detected under 25 rem• involves a decrease in white blood cells at

100 rem• includes nausea and fatigue over 100 rem• reduces white-cell count to zero over 300 rem • leads to death in 50% of people at 500 rem

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Nuclear Radiation

Half-Life of a Radioisotope

The age of the Dead Sea scrolls was determined using carbon-14.

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Half-Life

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

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Decay Curve

A decay curve shows• the decay of radioactive atoms• the remaining radioactive sample

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Half-lives of Some RadioisotopesHalf-lives of radioisotopes that are• naturally occurring tend to be long• used in nuclear medicine tend to be short

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• In one half-life, 40 mg of a radioisotope decays to 20 mg.

• After two half-lives, 10 mg of radioisotope remain.

40 mg x 1 x 1 = 10 mg 2 2

1 half-life 2 half-lives

Initial40 mg

20 mg10 mg

Half-Life Calculations

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Examples of Half-Lives

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Using Half-lives

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The half-life of iodine-123 is 13 h. How much of a 64-mg sample of I-23 is left after 26 h?

1) 32 mg

2) 16 mg

3) 8 mg

Learning Check

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Nuclear Radiation

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

• give off radiation that exposes a photographic plate (scan), giving an image of an organ

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Using a Scanner to Detect Radiation

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

Radioisotopes in Nuclear Medicine

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Learning Check

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

1) K-40 half-life 1.3 x 109 years

2) K-42 half-life 12 hours

3) I-131 half-life 8 days

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Positron Emission Tomography (PET)

In positron Emission Tomography (PET), • positrons are emitted from positron emitters such

as carbon -11, oxygen-15, and fluorine-18

• positrons are used to study brain function and metabolism

• positrons combine with electrons to produce gamma ray that can be detected, giving a three-dimensional image

18 18 09 8 1F O + e

0 0 01 1 0 + e e

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Positron Emission Tomography (PET)

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

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Computed Tomography (CT)

In computed tomography (CT), 30 000 X-rays• are directed at the brain in layers• are absorbed at different rates due to differences

in densities of body tissues and fluids• create three-dimensional images of the brain and

any tumors or hemorrhages

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Computed Tomography (CT)

A CT scan shows a brain tumor (yellow) on the right side of the brain.

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Magnetic Resonance Imaging (MRI)

In magnetic resonance imaging (MRI)• protons in the presence of a strong magnetic field

align with the magnetic field• protons release energy when magnetic field is

removed• protons in different environments emit energies of

different frequencies to provide images of soft tissue

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Magnetic Resonance Imaging (MRI)

An MRI scan provides images of the heart and lungs.

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Nuclear Radiation

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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Nuclear Fission

When a neutron bombards U-235,• an unstable nucleus of U-236 forms and

undergoes fission (splits)• smaller nuclei are produced such as Kr-91 and

Ba-142• neutrons are released to bombard more U-235

nuclei

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Nuclear Fission

1 235 236 91 142 10 92 92 36 56 0 + U U Kr + Ba + 3 + energyn n

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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 produce an atomic explosion

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Chain Reaction

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Learning Check

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

1 235 137 10 92 52 0 + U Te + ? + 2 + energyn n

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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 the fission process

Nuclear power plants supply about 10% of the electricity in the United States.

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Nuclear Power Plants

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Nuclear Fusion

Nuclear 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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Nuclear Fusion

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Indicate if each of the following is

1) nuclear fission or 2) 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

Learning Check

Concept Map

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