Nuclear Radiation
Natural Radioactivity
A person working with radioisotopes wears protective clothing and gloves and stands behind a shield.
1 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
2 Examples of Radioactive Isotopes
3 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?
4 Solution
Thallium-201 is used for heart scans to determine cardiac function. A. How many protons are in thallium-201? Thallium, symbol Tl, has 81 protons. B. How many neutrons are in thallium-201? mass number 201 atomic number 81 = 120 neutrons C. What is the atomic symbol of thallium-201? mass number 201 Tl atomic number 81
5 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
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
7 Beta Particle
A 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
8 Positron
A 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
9 Gamma () Ray
A 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
10 Summary of Common Forms of Nuclear Radiation
11 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
12 Solution
Mass Number Charge 1. alpha particle 4 2+ 2. positron 0 1+ 3. beta particle 0 1- 4. neutron 1 0 5. gamma ray 0 0
13 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
14 Radiation and Shielding Required
15 Radiation Protection
Different types of shielding are needed for different radiation particles.
16 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 A person working with radioisotopes wears protective clothing and gloves 4) lab coat and stands behind a shield. 5) thick concrete
17 Solution
Indicate the type of radiation (alpha, beta, and/or gamma) protection for each type of shielding. 1) heavy clothing alpha, beta 2) paper alpha 3) lead alpha, beta, gamma 4) lab coat alpha, beta 5) thick concrete alpha, beta, gamma
18 Nuclear Radiation
Nuclear Equations
A radon gas detector is used to determine radon levels in buildings with inadequate ventilation.
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 (, , , +)
20 Nuclear Equations
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
21 Balancing Nuclear Equations
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 = 238 238 234 4 92U 90 Th + 2 He Total = 92 = 92 Atomic Numbers
22 Guide to Completing a Nuclear Equation
23 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
24 Example of Writing an Equation for Alpha Decay 222 Write an equation for the alpha decay of 86 Rn STEP 1 Write the incomplete nuclear equation.
222 4 86Rn ? + 2 He STEP 2 Determine the missing mass number. 222 = ? + 4 222 – 4 = 218 218 = ? (mass number of new nucleus)
25 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 218 84 Po STEP 5 Complete the nuclear equation. 222 218 4 86Rn 84 Po + 2 He
26 Beta Decay
Beta decay occurs when • an electron (beta particle) is emitted from the nucleus • a neutron in the nucleus breaks down
1 0 1 0ne -1 + 1 H
27 Writing an Equation for a Beta Emitter Write an equation for the beta decay of potassium-42. STEP 1 Write the incomplete nuclear equation.
42 0 19K ? + -1e 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)
28 Writing an Equation for a Beta Emitter (continued) STEP 4 Determine the symbol of the new nucleus. Symbol of element 20 = Ca 42 20Ca
STEP 5 Complete the nuclear equation.
42 42 0 19K 20 Ca + -1e
29 Learning Check
Write the nuclear equation for the beta decay of Xe-133.
30 Solution
STEP 1 Write the incomplete nuclear equation.
133 0 54Xe ? + -1e STEP 2 Determine the missing mass number. 133 = ? + 0 133 0 = 133 = ? (mass number of new nucleus) STEP 3 Determine the missing atomic number. 54 = ? 1 54 + 1 = ? 55 = ? (atomic number of new nucleus)
31 Solution (continued)
STEP 4 Determine the symbol of the new nucleus. Symbol of element 55 = Cs
133 55 Cs STEP 5 Complete the nuclear equation.
133 133 0 54Xe 55 Cs + -1e
32 Positron Emission
In positron emission, • a proton is converted to a neutron and a positron
1 1 0 1H 0ne +1
• the mass number of the new nucleus is the same, but the atomic number decreases by 1
49 49 0 25Mn 24 Cr + +1e
33 Learning Check
Write the nuclear equation for the positron emission by Rb-82.
34 Solution
STEP 1 Write the incomplete nuclear equation.
82 0 37Rb ? + +1e STEP 2 Determine the missing mass number. 82 = ? + 0 82 = 82 = ? (mass number of new nucleus) STEP 3 Determine the missing atomic number. 37 = ? + 1 37 1 = ? 36 = ? (atomic number of new nucleus)
35 Solution (continued)
STEP 4 Determine the symbol of the new nucleus. Symbol of element 36 = Kr
82 36 Kr STEP 5 Complete the nuclear equation.
82 82 0 37Rb 36 Kr + +1e
36 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
99m 99 0 43Tc 43 Tc + 0
37 Summary of Types of Radiation
38 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
39 Learning Check
What radioactive isotope is produced when a neutron bombards cobalt-59 and an alpha particle is emitted?
59 1 4 27Co + 0n ? + 2 He
40 Solution
STEP 1 Write the incomplete nuclear equation.
59 1 4 27Co + 0n ? + 2 He STEP 2 Determine the missing mass number. 59 +1 = ? + 4 59 + 1 4 = 56 (mass number of new nucleus) STEP 3 Determine the missing atomic number. 27 = ? + 2 27 2 = ? 25 = ? (atomic number of new nucleus)
41 Solution (continued)
STEP 4 Determine the symbol of the new nucleus. Symbol of element 25 = Mn
56 25 Mn STEP 5 Complete the nuclear equation.
59 1 56 4 27Co + 0n 25 Mn + 2 He
42 Nuclear Radiation
Radiation Measurement
A radiation technician uses a Geiger Counter to check radiation levels.
43 Radiation Detection
A Geiger counter • detects beta and gamma radiation • uses ions produced by radiation to create an electrical current
44 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
45 Units of Radiation Measurement
46 Exposure to Radiation
Exposure to radiation occurs from • naturally occurring radioisotopes • medical and dental procedures • air travel, radon, and smoking cigarettes
47 Radiation Sickness
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
48 Nuclear Radiation
Half-Life of a Radioisotope
The age of the Dead Sea scrolls was determined using carbon-14.
49 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.
50 Decay Curve
A decay curve shows • the decay of radioactive atoms • the remaining radioactive sample
51 Half-lives of Some Radioisotopes Half-lives of radioisotopes that are • naturally occurring tend to be long • used in nuclear medicine tend to be short
52 Half-Life Calculations
• 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
Initial 1 half-life 2 half-lives 40 mg 20 mg 10 mg
53 Examples of Half-Lives
54 Using Half-lives
55 Learning Check
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
56 Solution
STEP 1 State the given and needed amounts of radioisotope. Given 64 mg of I-123; 13 h/half-life Need mg of I-123 remaining after 26 h
STEP 2 Write a plan to calculate amount of active radioisotope. number of hours Half - life number of half-lives mg of I-123 Number of mg of I-123 remaining half-lives
57 Solution (continued)
STEP 3 Write the half-life equality and conversion factors. 1 half-life = 13 h 1 half-life and 13 h 13 h 1 half-life STEP 4 Set up problem to calculate amount of active radioisotope. number of half-lives = 26 h x 1 half-life = 2 half-lives 13 h 13 h 13 h 64 mg 32 mg 16 mg 64 mg x ½ 32 mg x ½ = 16 mg (2)
58 Nuclear Radiation
Medical Applications Using Radioactivity
59 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
60 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.
61 Radioisotopes in Nuclear Medicine
62 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
63 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. 2) K-42 with a half-life of 12 h. 3) I-131 with a half-life 8 days.
64 Positron Emission Tomography (PET) In positron Emission Tomography (PET), • positrons are emitted from positron emitters such as carbon -11, oxygen-15, and fluorine-18 18 18 0 9F 8 O + 1e • 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 0 0 0 1ee + 1 0
65 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.
66 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
67 Computed Tomography (CT)
A CT scan shows a brain tumor (yellow) on the right side of the brain.
68 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
69 Magnetic Resonance Imaging (MRI)
An MRI scan provides images of the heart and lungs.
70 Nuclear Radiation
Nuclear Fission and Fusion
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
72 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
73 Nuclear Fission
1 235 236 91 142 1 0nn + 92 U 92 U 36 Kr + 56 Ba + 3 0 + energy
74 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
75 Chain Reaction
76 Learning Check
Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.
1 235 137 1 0nn + 92 U 52 Te + ? + 2 0 + energy
77 Solution
1 235 137 97 1 0nn + 92 U 52 Te + 40Zr + 2 0 + ene r g y
78 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.
79 Nuclear Power Plants
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
81 Nuclear Fusion
82 Learning Check
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
83 Solution
Indicate if each of the following is 1) nuclear fission or 2) nuclear fusion 1 A. a nucleus splits 1, 2 B. large amounts of energy are released 2 C. small nuclei form larger nuclei 2 D. hydrogen nuclei react 1 E. several neutrons are released
84 Concept Map
85