1. Atomic Nucleus and Radioactivity
Lesson 28
Atomic Nucleus and Radioactivity
Eleanor Roosevelt High School
Chin-Sung Lin

2. Atomic Nucleus and Radioactivity

3. X-Rays and Radioactivity
In 1895, a German physicist, W. C. Roentgen was working with a cathode ray tube in his lab and discovered X-rays produced by a beam of electrons striking the glass surface of a gas-discharge tube

4. X-Rays and Radioactivity
Roentgen found that X-rays could pass through solid materials, could ionize the air, showed no refraction in glass, and were undeflected by magnetic fields

5. X-Rays and Radioactivity
X-rays are high-frequency electromagnetic waves, usually emitted by the de-excitation of the innermost orbital electrons of atoms

6. X-Rays and Radioactivity
An energetic beam of electrons striking a solid surface excites the innermost electrons and produces higher-frequency photons of X-radiation.

7. X-Rays and Radioactivity
X-ray photons have high energy and can penetrate many layers of atoms before being absorbed or scattered
X-rays do this when they pass through your soft tissue to produce an image of the bones inside your body

8. X-Rays and Radioactivity
Radioactivity is the process of nuclear decay (radioactive decay)
Nothing new in the environment; it’s been going on since time zero
It warms Earth’s interior, is in the air we breathe, and is present in all rocks (some in trace amounts)
It is natural

9. The radioactive decay of nature’s elements occurs in the
X-Rays and Radioactivity
CHECK YOUR NEIGHBOR
The radioactive decay of nature’s elements occurs in the
A. soil we walk on.
air we breathe.
interior of Earth.
All of the above.
D. all of these.

10. X-Rays and Radioactivity
CHECK YOUR ANSWER
The radioactive decay of nature’s elements occurs in the
A. soil we walk on.
air we breathe.
interior of Earth.
All of the above.
D. all of these.

11. Alpha, Beta, and Gamma Rays

12. Alpha, Beta, and Gamma Rays

13. Alpha, Beta, and Gamma Rays
Radioactive elements emit three distinct types of radiation:
 — alpha: positively charged (helium nuclei)
 — beta: negatively charged (electrons)
 — gamma: no charge(electromagnetic radiation)
Relative penetration

14. The origins of radioactivity go back to
Alpha, Beta, and Gamma Rays
CHECK YOUR NEIGHBOR
The origins of radioactivity go back to
A. military activities in the mid-20th century.
the Industrial Revolution two centuries ago.
the beginning of human error.
before humans emerged on Earth.
D. before humans emerged on Earth.

15. The origins of radioactivity go back to
Alpha, Beta, and Gamma Rays
CHECK YOUR ANSWER
The origins of radioactivity go back to
A. military activities in the mid-20th century.
the Industrial Revolution two centuries ago.
the beginning of human error.
before humans emerged on Earth.
D. before humans emerged on Earth.

16. Alpha, Beta, and Gamma Rays
Alpha decay

17. Alpha, Beta, and Gamma Rays
Alpha decay

18. Alpha, Beta, and Gamma Rays
Beta decay

19. Alpha, Beta, and Gamma Rays
Beta decay

20. Alpha, Beta, and Gamma Rays
Beta decay

21. Alpha, Beta, and Gamma Rays
Beta decay

22. Alpha, Beta, and Gamma Rays
Gamma decay

23. Alpha, Beta, and Gamma Rays
Gamma decay

24. Any atom that emits an alpha particle or beta particle
Alpha, Beta, and Gamma Rays
CHECK YOUR NEIGHBOR
Any atom that emits an alpha particle or beta particle
A. becomes an atom of a different element, always.
may become an atom of a different element.
becomes a different isotope of the same element.
increases its mass.
A. becomes an atom of a different element, always.

25. Any atom that emits an alpha particle or beta particle
Alpha, Beta, and Gamma Rays
CHECK YOUR ANSWER
Any atom that emits an alpha particle or beta particle
A. becomes an atom of a different element, always.
may become an atom of a different element.
becomes a different isotope of the same element.
increases its mass.
A. becomes an atom of a different element, always.

26. Which of these is actually a high-speed electron?
Alpha, Beta, and Gamma Rays
CHECK YOUR NEIGHBOR
Which of these is actually a high-speed electron?
A. Alpha
Beta
Gamma
B. Beta.

27. Alpha, Beta, and Gamma Rays
CHECK YOUR ANSWER
Which of these is actually a high-speed electron?
A. Alpha
Beta
Gamma
B. Beta.

28. Radioactive Isotopes
The number of protons in an atomic nucleus determine the number of electrons surrounding the nucleus in a neutral atom
When there is a different number of electrons than the nuclear protons, the atom is charged and is called an ion
When there is a same number of protons (atomic numbers) but different number of neutrons (mass numbers), they are called isotopes
When an isotope is radioactive, it is called radioactive isotope

29. Radioactive Isotopes
Three common isotopes of Hydrogen:

30. Radioactive Isotopes
Tritium is a radioactive isotope:

31. Radioactive Isotopes
Tritium is a radioactive isotope:

32. Exercise: Radioactive Isotopes
The nucleus of beryllium-8 (Be-8) undergoes a special kind of radioactive decay: it split into two equal halves. What nuclei are the products of this decay? What is the form of this decay?

33. Exercise: Radioactive Isotopes
The nucleus of beryllium-8 (Be-8) undergoes a special kind of radioactive decay: it split into two equal halves. What nuclei are the products of this decay? What is the form of this decay?
8Be –> 2 4He
alpha decay 2 4

34. Radioactive Isotopes
The electric force of repulsion between the protons in a heavy nucleus acts over a greater distance than the attractive forces among the neutrons and protons in the nucleus
Each proton is repelled by every other proton in the nucleus, but is attracted only by the nucleons closest to it
In a large nucleus, electric repulsion can exceed nuclear attraction
This instability makes all the heaviest atoms radioactive

35. The Atomic Nucleus and the Strong Force
The strong force is more effective with smaller nuclei.
particles occupying the nucleus is nucleons
Mass=2000 times the mass of electrons

36. The Atomic Nucleus and the Strong Force
The strong force holds nucleons together
Nuclear force holds the nucleus together called the strong interaction which is an attractive force and is a short range force
Electrical interaction is a long range force

37. The Atomic Nucleus and the Strong Force
A lone neutron is radioactive and spontaneously transforms to a proton and an electron
A neutron needs protons around to keep this from happening

38. The Atomic Nucleus and the Strong Force
Alpha emission

39. The Atomic Nucleus and the Strong Force
CHECK YOUR NEIGHBOR
The strong force is a force in the
A. atom that holds electrons in orbit.
nucleus that holds nucleons together.
Both A and B.
Neither A nor B.
B. nucleus that holds nucleons together.

40. The Atomic Nucleus and the Strong Force
CHECK YOUR ANSWER
The strong force is a force in the
A. atom that holds electrons in orbit.
nucleus that holds nucleons together.
Both A and B.
Neither A nor B.
B. nucleus that holds nucleons together.

41. The Atomic Nucleus and the Strong Force
CHECK YOUR NEIGHBOR
In the nucleus of an atom, the strong force is a relatively
A. short-range force.
long-range force.
unstable force.
neutralizing force.
A. short-range force.

42. The Atomic Nucleus and the Strong Force
CHECK YOUR ANSWER
In the nucleus of an atom, the strong force is a relatively
A. short-range force.
long-range force.
unstable force.
neutralizing force.
A. short-range force.

43. Radioactive Half-Life
The rate of decay for a radioactive isotope is measured in terms of a characteristic time, the half-life, the time for half of an original quantity of an element to decay

44. Radioactive Half-Life
CHECK YOUR NEIGHBOR
Suppose the number of neutrons in a reactor that is starting up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion?
A. 1 minute
2 minutes
5 minutes
9 minutes
D. 9 minutes.

45. Radioactive Half-Life
CHECK YOUR ANSWER
Suppose the number of neutrons in a reactor that is starting up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion?
A. 1 minute
2 minutes
5 minutes
9 minutes
Explanation:
This question would be appropriate with Appendix D, Exponential Growth and Doubling Time. Can you see that working backward, each minute has half the number of neutrons?
D. 9 minutes.

46. Radiation Half-Life CHECK YOUR NEIGHBOR
A certain isotope has a half-life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be
A. zero.
one-quarter.
Half.
the same.
C. half.

47. Radiation Half-Life CHECK YOUR ANSWER
A certain isotope has a half-life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be
A. zero.
one-quarter.
Half.
the same.
C. half.

48. Exercise: Radioactive Half-Life
If a sample of radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the second year?

49. Exercise: Radioactive Half-Life
If a sample of radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the second year?
(1/2)2 = 1/4

50. Exercise: Radioactive Half-Life
If Fukushima Daiichi nuclear power plant in Japan releases a certain amount of radioactive iodine (I-131), how many percent of the original material will be left at the end of the 50 days? (The half-life of I-131 is 8.02 day)

51. Exercise: Radioactive Half-Life
If Fukushima Daiichi nuclear power plant in Japan releases a certain amount of radioactive iodine (I-131), how many percent of the original material will be left at the end of the 50 days? (The half-life of I-131 is 8.02 day)
(1/2) (50 d/8.02 d) = 1.33%

52. Exercise: Radioactive Half-Life
The half-life of Th-227 is 18.2 day. How many days are required for 0.70 of a given sample to decay?

53. Exercise: Radioactive Half-Life
The half-life of Th-227 is 18.2 day. How many days are required for 0.70 of a given sample to decay?
(1/2) (t/18.2 days) = (1.0 – 0.7)
t = days

54. Radioactive Half-Life
Radioactive decay series:
Uranium-238 to lead-206 through a series of alpha and beta decays
In 4.5 billion years, half the uranium presently in Earth will be lead

55. Alpha, Beta, and Gamma Rays
Irradiation is the process by which an item is exposed to radiation
Food irradiation kills microbes, but doesn’t make the food radioactive

56. Alpha, Beta, and Gamma Rays
CHECK YOUR NEIGHBOR
Which of these is the nucleus of the helium atom?
A. Alpha
Beta
Gamma
All are different forms of helium.
A. Alpha.

57. Which of these is the nucleus of the helium atom?
Alpha, Beta, and Gamma Rays
CHECK YOUR ANSWERS
Which of these is the nucleus of the helium atom?
A. Alpha
Beta
Gamma
All are different forms of helium
Explanation:
Contrary to the failures of alchemists of old to change elements from one to another, this was going on all around them—unnoticed
A. Alpha.

58. Transmutation of the Elements
Transmutation: The changing from one chemical element to another
With alpha or beta particle, a different element is formed. This is transmutation, which occurs in natural events and is also initiated artificially in the laboratory
Uranium naturally transmutes to Thorium when an alpha particle is emitted

59. Transmutation of the Elements
Uranium naturally transmutes to Thorium when an alpha particle is emitted

60. Transmutation of the Elements
Natural transmutation
Thorium naturally transmutes to protactinium when a beta particle is emitted.
An electron is e
Superscript 0 indicates electron’s mass is insignificant compared with nucleons
Subscript -1 is the electric charge of the electron

61. Radioactive Half-Life
U-238 Radioactive decay series

62. Transmutation of the Elements
CHECK YOUR NEIGHBOR
When an element ejects an alpha particle, the atomic number of the resulting element
A. reduces by 2.
reduces by 4.
increases by 2.
increases by 4.
A. reduces by 2.

63. Transmutation of the Elements
CHECK YOUR ANSWER
When an element ejects an alpha particle, the atomic number of the resulting element
A. reduces by 2.
reduces by 4.
increases by 2.
increases by 4.
Explanation:
An alpha particle (a helium nucleus) has atomic number 2. Ejection of an alpha particle means a loss of 2 protons, so the atomic number of the element is lowered by 2
A. reduces by 2.

64. Transmutation of the Elements
CHECK YOUR NEIGHBOR
When an element ejects an alpha particle and a beta particle, the atomic number of that element
A. reduces by 1.
increases by 1.
reduces by 2.
increases by 2.
A. reduces by 1.

65. Transmutation of the Elements
CHECK YOUR ANSWER
When an element ejects an alpha particle and a beta particle, the atomic number of that element
A. reduces by 1.
increases by 1.
reduces by 2.
increases by 2.
Explanation:
Alpha emission reduces atomic number by 2, and beta emission increases atomic number by 1, so net result is 1.
A. reduces by 1.

66. Exercise: Transmutation of the Elements
Write the nuclear reactions from Uranium-238 to lead-206 through a series of alpha and beta decays

67. Transmutation of the Element
Artificial transmutation
An alpha particle fired at and impacting on a nitrogen atom, which transmutes to oxygen and hydrogen

68. Atoms can transmute into completely different atoms in
Transmutation of the Elements
CHECK YOUR NEIGHBOR
Atoms can transmute into completely different atoms in
A. nature.
laboratories.
Both A and B.
Neither A nor B.
C. Both A and B.

69. Atoms can transmute into completely different atoms in
Transmutation of the Elements
CHECK YOUR ANSWER
Atoms can transmute into completely different atoms in
A. nature.
laboratories.
Both A and B.
Neither A nor B.
Explanation:
Atomic transmutation occurs in nature, in laboratories, and as far as we know, throughout the cosmos
C. Both A & B.

70. Transmutation of the Elements
CHECK YOUR NEIGHBOR
An element emits 1 beta particle, and its product then emits 1 alpha particle. The atomic number of the resulting element is changed by
A. 0.
-1.
-2.
None of the above.
B. minus 1.

71. Transmutation of the Elements
CHECK YOUR ANSWER
An element emits 1 beta particle, and its product then emits 1 alpha particle. The atomic number of the resulting element is changed by
A. 0.
-1.
-2.
None of the above.
Explanation:
Beta emission increases atomic number by 1, then alpha emission decreases atomic number by 2, so the net change is –1.
B. minus 1.

72. Radiation Detectors
Geiger counter detects incoming radiation by a short pulse of current triggered when radiation ionizes a gas in the tube

73. Radiation Detectors
Scintillation counter indicates incoming radiation by flashes of light produced when charged particles or gamma rays pass through the counter

74. Radiation Detectors Cloud chamber:
Charged particles moving through supersaturated vapor leave trails
When the chamber is in a strong electric or magnetic field, bending of the tracks provides information about the charge, mass, and momentum of the particles

75. Radiation Detectors Bubble chamber:
Liquid hydrogen is heated under pressure in a glass and stainless steel chamber to a point just short of boiling
If the pressure in the chamber is suddenly released at the moment an ion-producing particle enters, a thin trail of bubbles is left along the particle’s path

76. Radiation Units
Different units of measure are used depending on what aspect of radiation is being measured
The amount of radiation being emitted
The radiation dose absorbed by a person
The biological risk of exposure to radiation

77. Radiation Units Aspect Conventional SI
The amount of radiation being emitted
Curie (Ci)
Becquerel (Bq)
The radiation dose absorbed by a person
Rad (rad)
Gray (Gy)
The biological risk of exposure to radiation
Rem (rem)
Sievert (Sv)

78. Radiation Units – Ci and Bq
The amount of radiation being emitted, by a radioactive material is measured using the conventional unit curie (Ci), or the SI unit becquerel (Bq)
of radioactive atoms in a radioactive material over a period of time
1 Bq = 1 disintegration per second
1 Ci = 37 X 109 Bq
Ci or Bq may be used to refer to the amount of radioactive materials released into the environment

79. Radiation Units – rad and Gy
The radiation dose absorbed by a person (that is, the amount of energy deposited per unit of weight of human tissue by radiation) is measured using the conventional unit rad or the SI unit gray (Gy)
The rad, which stands for radiation absorbed dose, was the conventional unit of measurement
1 Gy = 100 rad

80. Radiation Units – rem and Sv
The biological risk of exposure to radiation is measured using the conventional unit rem or the SI unit sievert (Sv)
Scientists have assigned a number, Quality Factor (Q), to each type of ionizing radiation (alpha and beta particles, gamma rays, and x-rays) depending on that type's ability to transfer energy to the cells of the body
To estimate a person's biological risk in rems
rem = rad X Q
1 Sv = 100 rem

81. Environmental Radiation
Units of radiation
Particle Radiation Quality Factor Health effect
alpha 1 rad  = 10 rems
beta 10 rad  = 10 rems
Doses of radiation
Lethal doses of radiation begin at 500 rems

82. Environmental Radiation
Source received annually
Natural origin Typical dose (mrem)
Cosmic radiation
Ground
Air (Radon-222)
Human tissues (K-40; Ra-226)

83. Environmental Radiation
Radon, a common environmental hazard
Most radiation from natural background
About 1/5 from nonnatural sources

84. Environmental Radiation
Doses of radiation
Human origin Typical dose (mrem)
Medical procedures
Diagnostic X-rays
Nuclear diagnostics
TV tubes, other consumer products
Weapons-test fallout
Commercial fossil-fuel power plants < 1
Commercial nuclear power plants << 1

85. Environmental Radiation
Radioactive tracers
Radioactive isotopes used to trace such pathways are called tracers

86. Radiometric Dating
Earth’s atmosphere is continuously bombarded by cosmic rays, which causes many atoms in the upper atmosphere to transmute

87. Radiometric Dating
A nitrogen that captures a neutron and becomes an isotope of carbon by emitting a proton:

88. Radiometric Dating
Because living plants take in carbon dioxide, any C-14 lost by decay is immediately replenished with fresh C-14 from the atmosphere
Dead plants continue emitting C-14 without replenishment

89. Radiometric Dating
Carbon-14 is a beta emitter and decays back to nitrogen
The half-life of Carbon-14 is about 5730 years

90. Radiometric Dating
Relative amounts of C-12 to C-14 enable dating of organic materials

91. Radiometric Dating CHECK YOUR NEIGHBOR
The half-life of carbon-14 is about 5730 years, which means that the present amount in your bones will reduce to zero
A. when you die.
in about 5730 years.
in about twice 5730 years.
None of the above.
D. none of these.

92. Radiometric Dating CHECK YOUR ANSWER
The half-life of carbon-14 is about 5730 years, which means that the present amount in your bones will reduce to zero
A. when you die.
in about 5730 years.
in about twice 5730 years.
None of the above.
Explanation:
In theory, the amount never reaches zero. In eons to come, trace amounts of the carbon-14 in your bones, even if completely dissolved, will still exist.
D. none of the above.

93. Q & A

94. The End