1. Chapter 9 Nuclear Radiation
9.1
Natural Radioactivity

2. 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

3. 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.

4. 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.

5. Learning Check
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

6. 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

7. 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

8. Shielding for Radiation Protection

9. Learning Check What type of radiation will be blocked by
A. lead shield
B. paper, clothing

10. Solution What type of radiation will be blocked by
A. lead shield gamma radiation
B. paper, clothing alpha radiation

11. Chapter 9 Nuclear Radiation
9.2
Nuclear Equations

12. 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: =
251Cf  Cm He
Atomic number sum: =

13. Guide to Balancing Nuclear Equations

14. 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.

15. 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

16. 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.

17. 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.

18. 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

19. 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.

20. Learning Check
Write the nuclear equation for the beta decay of 60Co.

21. 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 = 60
Step 3 Determine the missing atomic number.
27  (1) = 28

22. 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.

23. 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.

24. 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

25. Summary of Types of Radiation

26. 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
When nonradioactive B-10 is bombarded by an alpha particle, the products are radioactive N-13 and a neutron.

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

28. 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.
 4 = 95
Step 3 Determine the missing atomic number.
27  2 = 25

29. 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.

30. Chapter 9 Nuclear Radiation
9.3
Radiation Measurement

31. Geiger Counter A Geiger counter detects beta and gamma radiation
uses ions produced by radiation to create an electrical current

32. 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

33. 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.

34. Radiation Exposure Exposure to radiation occurs from
naturally occurring radioisotopes
medical and dental procedures
air travel, radon, and smoking cigarettes
cosmic rays

35. 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

36. 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 MBq
B  106 MBq
C  102 MBq

37. 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  Ci  3.7  1010 Bq  1 MBq x
1 x 106 Ci Ci  106 Bq
= 3.7 MBq The answer is A.

38. Chapter 9 Nuclear Radiation
9.4
Half-Life of a Radioisotope

39. 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.
The decay curve for I-131 shows that one-half the sample
decays every 8 days.

40. Half-Lives of Some Radioisotopes

41. Guide to Using Half-Lives

42. 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 years?
Step 1 State the given and needed quantities.
Given: 36 mg, years, half-life of 38.1 years
Needed: 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 mg Sr-90 remaining

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

44. 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 years?
Step 4 Set up the problem to calculate amount of active radioisotope.
Number of half-lives
4 years x 1 half-life = 4 half-lives
38.1 years
1 half-life half-lives 3 half-lives 4 half-lives
36 mg  18 mg  9 mg  mg  2.3 mg Sr-90

45. 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?

46. Solution
Carbon-14 was used to determine the age of the Dead Sea Scrolls. If the Dead Sea Scrolls were determined to be 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 = half-life
5730 years

47. 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 mg
B. 16 mg
C. 8 mg

48. 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 hours
Needed: 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 mg I-123 remaining

49. 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 half-life
1 half-life hours

50. 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-lives
26 hours x 1 half-life = 2 half-lives
13 hours
1 half-life half-lives
64 mg  32 mg  16 mg I-123
The answer is B, 16 mg of I-123 remain.

51. Chapter 9 Nuclear Radiation
9.5
Medical Applications Using Radioactivity

52. 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

53. Medical Applications of Radioisotopes

54. 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

55. Scans with Radioisotopes
(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.

56. 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

57. 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.

58. Computed Tomography (CT)
A computer monitors the absorption of X-ray beams directed at the brain in successive layers.
Differences in absorption based on tissue densities and fluids provide images of the brain.

59. Magnetic Resonance Imaging (MRI)
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

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

61. 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

62. 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.

63. Chapter 9 Nuclear Radiation
9.6
Nuclear Fission and Fusion

64. 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

65. 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

66. Nuclear Fission Diagram
1n U U Kr Ba n + energy

67. 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.

68. 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.

69. Learning Check 1n + 235U 137Te + ?X + 2 1n + energy 0 92 52 ? 0
Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.
1n U Te + ?X n + energy ?

70. Solution 1n + 235U 137Te + 97Zr + 2 1n + energy 0 92 52 40 0
Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.
1n U Te Zr n + energy

71. 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

72. Nuclear Fusion
Fusion
occurs at extremely high temperatures ( C)
combines small nuclei into larger nuclei
releases large amounts of energy
occurs continuously in the sun and stars
Hydrogen atoms combine in a fusion reactor at very high temperatures.

73. 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.

74. 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.

75. Nuclear Radiation – Concept Map