1. Chapter 30
Nuclear Physics

2. 30 Nuclear Physics
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6. Nuclear Structure
Different isotopes of the same element have the same atomic number but different mass numbers.
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7. Checking Understanding
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: A
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8. Answer
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: A
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9. Checking Understanding
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: B
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10. Answer
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: B
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11. Checking Understanding
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: C
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12. Answer
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: C
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13. Checking Understanding
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: D
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14. Answer
How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.) 8 7 6 5 4
Answer: D
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15. Checking Understanding
Boron, with atomic number Z=5, has two stable isotopes, with atomic mass numbers A=10 and A=11. Boron’s chemical atomic mass is What are the approximate fractions of the two stable boron isotopes found in nature?
A. 92% 11B, 8% 10B
B. 80% 11B, 20% 10B
C. 50% 11B, 50% 10B
D. 20% 11B, 80% 10B
E. 8% 11B, 92% 10B
Answer: B
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16. How do I find out about Elemental abundances
Web Elements is a good site at URL:

17. Answer
Boron, with atomic number Z=5, has two stable isotopes, with atomic mass numbers A=10 and A=11. Boron’s chemical atomic mass is What are the approximate fractions of the two stable boron isotopes found in nature?
A. 92% 11B, 8% 10B
B. 80% 11B, 20% 10B
C. 50% 11B, 50% 10B
D. 20% 11B, 80% 10B
E. 8% 11B, 92% 10B
Answer: B
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18. Example Problem
Magnesium has three stable isotopes, with the following natural abundances:
79% of naturally occurring magnesium is 24Mg, with u=23.99
10% of naturally occurring magnesium is 25Mg, with u=24.99
11% of naturally occurring magnesium is 26Mg, with u=25.98
What is the chemical atomic mass of magnesium?
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19. Stability
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20. Example Problems
There are several elements for which there is only one stable isotope, or for which one stable isotope dominates the natural abundance. Three examples are:
All but % of naturally occurring helium is the stable isotope 4He.
100% of naturally occurring niobium is the stable isotope 93Nb.
100% of naturally occurring bismuth is the stable isotope 209Bi.
What is the ratio of neutrons to protons for these three isotopes?
16O, with u= , is stable; 19O, with u= , is not. What is the binding energy per nucleon for each of these nuclei?
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21. Binding Energy
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22. Binding Energy of a Helium Nucleus
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23. Curve of Binding Energy
Light nuclei can become more stable through fusion.
Heavy nuclei can become more stable through fission.
All nuclei larger than a certain size spontaneously fission.
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24. Nuclear Forces
Two protons also experience a smaller electrostatic repulsive force, but it is smaller than the strong nuclear force!
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25. Nuclear Energy Levels and Decay
Different levels for neutrons and protons
Energy difference between levels is very large
Nuclei can become more stable through certain decay modes
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26. Example Problem
The beryllium isotope 11Be decays to the boron isotope 11B.
Show the nucleons of both nuclei on the shell-model energy-level diagrams below.
Explain why this decay is energetically favorable.
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27. Nuclear Radiation
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28. Alpha Decay
Nothing missing here.
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29. Beta Decay
They did not show the neutrino, neutron goes to proton + electron + electron neutrino or proton goes to neutron + positron (positive electron) + electron neutrino
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30. Checking Understanding
What is the daughter nucleus for this decay:
90Sr → ?X+e-
90Y
89Y
90Rb
89Rb
Answer: A
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31. Answer What is the daughter nucleus for this decay: 90Sr → ?X+e- 90Y
90Rb
89Rb
Answer: A
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32. Checking Understanding
What is the daughter nucleus for this decay:
222Rn → ?X+α
220Po
218Po
220Ra
218Ra
Answer: B
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33. Answer What is the daughter nucleus for this decay: 222Rn → ?X+α 220Po
220Ra
218Ra
Answer: B
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34. Checking Understanding
What is the daughter nucleus for this decay:
99Tc → ?X+γ
99Tc
99Mo
99Nb
99Ru
Answer: A
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35. Answer What is the daughter nucleus for this decay: 99Tc → ?X+γ 99Tc
99Mo
99Nb
99Ru
Answer: A
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36. Example Problem
11Li is an unstable isotope of lithium. Sketch the energy level structure for the neutrons and the protons in this nucleus. What decay mode would you expect for this nucleus? Write the full equation for the decay you expect, including the daughter nucleus.
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37. Operation of a Geiger Counter
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38. Example Problem: Activity
0.693N
t1/2
______
R = rN =
Most of the internal radiation of the human body is due to a single isotope, the beta emitter 40K, with half life of 1.28×109 years. The body contains about 0.35% potassium by mass; of this potassium, about 0.012% is 40K. What is the total activity, in Bq, of a 70 kg human?
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39. Half Life
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40. Nuclear Decay
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41. Example Problems: Decay Times
The Chernobyl nuclear reactor accident in the Soviet Union in 1986 released a large plume of radioactive isotopes into the atmosphere. Of particular health concern was the short-lived (half life: 8.0 days) isotope 131I, which, when ingested, is concentrated in and damages the thyroid gland. This isotope was deposited on plants that were eaten by cows, which then gave milk with dangerous levels of 131I. This milk couldn’t be used for drinking, but it could be used to make cheese, which can be stored until radiation levels have decreased. How long would a sample of cheese need to be stored until the number of radioactive atoms decreased to 3% of the initial value?
A scrap of parchment from the Dead Sea Scrolls was found to have a 14C/12C ratio that is 79.5% of the modern value. Determine the age of this parchment.
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42. Dose and Dose Equivalent
1 Gy = 1.00 J/kg of absorbed energy
Dose equivalent in Sv = (dose in Gy) x RBE
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43. Example Problems: Determining Dose
In a previous example, we computed the activity of the 40K in a typical person. Each 40K decay produces a 1.3 MeV beta particle. If 40% of the energy of these decays is absorbed by the body, what dose, and what dose equivalent, will a typical person receive in one year from the decay of these nuclei in the body?
A passenger on an airplane flying across the Atlantic will receive an extra radiation dose of about 5 microsieverts per hour from cosmic rays. How many hours of flying would it take in one year for a person to double his or her yearly radiation dose? Assume there are no other significant radiation sources besides natural background.
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44. Conceptual Example Problem: Radioactive Cookies
Suppose you have three cookies, each of which is radioactive. They have the same activity, but one is an alpha source, one a beta source, and one a gamma source. You must put one cookie in your pocket, eat one, and place one in a lead box. Which one do you put in the lead box, which one do you eat, and which one do you put in your pocket?
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45. Summary
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46. Summary
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47. Additional Questions What is the decay mode of the following decay?
137Cs → 137Ba + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: B
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48. Answer What is the decay mode of the following decay?
137Cs → 137Ba + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: B
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49. Additional Questions What is the decay mode of the following decay?
222Rn → 218Po + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: A
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50. Answer What is the decay mode of the following decay?
222Rn → 218Po + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: A
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51. Additional Questions What is the decay mode of the following decay?
60Ni* → 60Ni + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: D
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52. Answer What is the decay mode of the following decay? 60Ni* → 60Ni + ?
Alpha decay
Beta-minus decay
Beta-plus decay
Gamma decay
Answer: D
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53. Additional Example Problem
A 60 kg laboratory worker receives a whole-body
x-ray exposure of 0.50 mSv. The x-ray wavelength is 0.15 nm. How many x-ray photons are absorbed in the worker’s body? X rays have an RBE of 1.
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