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Chapter 30. 0. Nuclear Physics. 30 Nuclear Physics. Slide 30-2. Slide 30-3. Slide 30-4. Slide 30-5. Reading Quiz. The mass number A of a nucleus is the number of ___________ in the nucleus. protons protons plus neutrons neutrons. Slide 30-6. Answer.

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chapter 30

Chapter 30

0

Nuclear Physics

slide6

Reading Quiz

  • The mass number A of a nucleus is the number of ___________ in the nucleus.
    • protons
    • protons plus neutrons
    • neutrons

Slide 30-6

slide7

Answer

  • The mass number A of a nucleus is the number of ___________ in the nucleus.
    • protons
    • protons plus neutrons
    • neutrons

Slide 30-7

slide8

Reading Quiz

  • When a nucleus decays by giving off an electron, we call this ________ decay.
    • alpha
    • beta
    • gamma

Slide 30-8

slide9

Answer

  • When a nucleus decays by giving off an electron, we call this ________ decay.
    • alpha
    • beta
    • gamma

Slide 30-9

slide10

Reading Quiz

  • ________ decay results in a daughter nucleus that is the same as the parent nucleus.
    • Alpha
    • Beta
    • Gamma

Slide 30-10

slide11

Answer

  • ________ decay results in a daughter nucleus that is the same as the parent nucleus.
    • Alpha
    • Beta
    • Gamma

Slide 30-11

slide12

Nuclear Structure

Different isotopes of the same element have the same atomic number but different mass numbers.

Slide 30-12

slide13

Checking Understanding

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-13

slide14

Answer

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-14

slide15

Checking Understanding

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-15

slide16

Answer

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-16

slide17

Checking Understanding

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-17

slide18

Answer

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-18

slide19

Checking Understanding

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-19

slide20

Answer

  • How many neutrons are in the following isotope? (The isotope may be uncommon or unstable.)
    • 8
    • 7
    • 6
    • 5
    • 4

Slide 30-20

slide21
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 10.81. 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

Checking Understanding

Slide 30-21

slide22
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 10.81. 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

Slide 30-22

slide23
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?

Example Problem

Slide 30-23

slide24

Stability

Slide 30-24

slide25

Binding Energy

Slide 30-26

slide27
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 0.00013% 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=15.994915, is stable; 19O, with u=19.003577, is not. What is the binding energy per nucleon for each of these nuclei?

Example Problems

Slide 30-25

slide28

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.

Slide 30-28

slide29

Nuclear Forces

Slide 30-29

slide30

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

Slide 30-30

slide31

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.

Slide 30-31

slide33

Alpha Decay

Slide 30-33

slide34

Beta Decay

Slide 30-34

slide35

Checking Understanding

  • What is the daughter nucleus for this decay:
  • 90Sr → ?X+e-
    • 90Y
    • 89Y
    • 90Rb
    • 89Rb

Slide 30-35

slide36

Answer

  • What is the daughter nucleus for this decay:
  • 90Sr → ?X+e-
    • 90Y
    • 89Y
    • 90Rb
    • 89Rb

Slide 30-36

slide37

Checking Understanding

  • What is the daughter nucleus for this decay:
  • 222Rn → ?X+α
    • 220Po
    • 218Po
    • 220Ra
    • 218Ra

Slide 30-37

slide38

Answer

  • What is the daughter nucleus for this decay:
  • 222Rn → ?X+α
    • 220Po
    • 218Po
    • 220Ra
    • 218Ra

Slide 30-38

slide39

Checking Understanding

  • What is the daughter nucleus for this decay:
  • 99Tc → ?X+γ
    • 99Tc
    • 99Mo
    • 99Nb
    • 99Ru

Slide 30-39

slide40

Answer

  • What is the daughter nucleus for this decay:
  • 99Tc → ?X+γ
    • 99Tc
    • 99Mo
    • 99Nb
    • 99Ru

Slide 30-40

slide41

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.

Slide 30-41

slide42

Decay Series

  • 235U is unstable
  • Through a series of alpha beta decay, settles on 207Pb
  • In a star, everything ends up as 56Fe

Slide 30-41

slide43

Fission

Slide 30-46

slide45

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?

Slide 30-43

slide46

Half Life

Slide 30-44

slide47

Nuclear Decay

Slide 30-45

slide48

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?

Slide 30-46

slide49

Example Problems: Decay Times

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.

Slide 30-46

slide50

Dose and Dose Equivalent

1 Gy = 1.00 J/kg of absorbed energy

Dose equivalent in Sv = (dose in Gy) x RBE

Slide 30-47

slide51

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?

Slide 30-48

slide52

Summary

Slide 30-50

slide53

Summary

Slide 30-51

slide54

Additional Questions

  • What is the decay mode of the following decay?
  • 137Cs → 137Ba + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-52

slide55

Answer

  • What is the decay mode of the following decay?
  • 137Cs →137Ba + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-53

slide56

Additional Questions

  • What is the decay mode of the following decay?
  • 222Rn → 218Po + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-54

slide57

Answer

  • What is the decay mode of the following decay?
  • 222Rn →218Po + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-55

slide58

Additional Questions

  • What is the decay mode of the following decay?
  • 60Ni* → 60Ni + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-56

slide59

Answer

  • What is the decay mode of the following decay?
  • 60Ni* →60Ni + ?
    • Alpha decay
    • Beta-minus decay
    • Beta-plus decay
    • Gamma decay

Slide 30-57

slide60

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.

Slide 30-58

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