1. Nuclear Chemistry Courtesy I. Markic
Topic 12
Nuclear Chemistry
Courtesy I. Markic

2. Nuclear Chemistry rev. 11/19/08
The study of nuclear reactions and their uses in chemistry
When nuclei change spontaneously, emitting radiation, they are said to be radioactive

3. Radioactive elements are used in medicine as… diagnostic tools
Nuclear Chemistry rev. 11/19/08
Radioactive elements are used in medicine as…
diagnostic tools
treatment for cancer
determine mechanisms for chemical reactions
trace movements of atoms in biological systems
Radioactive elements are used in archeology…
To date important historical artifacts
Uses of nuclear reactions…
generate electricity
create WMDs of property and/or life

4. Radioactivity Radioactive nuclei are called radionuclides
Nuclear Chemistry rev. 11/19/08
Radioactive nuclei are called radionuclides
Atoms containing radioactive nuclei are called radioisotopes
Atoms with the same atomic number but different mass numbers are called isotopes
Different isotopes of an element are distinguished by their mass numbers
Different nuclei have different stabilities
The nuclear properties of an atom depend on the ratio of neutrons to protons in its nucleus

5. Types of Radioactive Decay
Nuclear Chemistry rev. 11/19/08
Types of Radioactive Decay
The most common types…
alpha decay α 2He4
beta decay β -1e0 or -1β 0
gamma radiation  00 or just 

6. Nuclear Chemistry rev. 11/19/08
+ Battery -

7. Nuclear Chemistry rev. 11/19/08

8. Alpha Radiation α 2He4 Contains 2 protons and 2 neutrons
Nuclear Chemistry rev. 11/19/08
Alpha Radiation
α 2He4
Contains 2 protons and 2 neutrons
Has heavy mass, does not travel far…| …stopped by a thin sheet of paper or skin
Dangerous if ingested
92U  90Th He4 α emission
92U He4  94Pu242 α absorption

9. Beta Radiation β -1e0 or -1 β 0 Less charge than alpha particle
Nuclear Chemistry rev. 11/19/08
Beta Radiation
β -1e0 or -1 β 0
Less charge than alpha particle
Extremely small mass
More penetrating, can pass through paper… …stopped by aluminum foil or thin pieces of wood
6C  7N e0 β emission
19K e0  18Ar42 β absorption

10. Gamma Radiation  00 or just  No mass, no charge High energy photon
Nuclear Chemistry rev. 11/19/08
Gamma Radiation
 00 or just 
No mass, no charge
High energy photon
Often emitted with α or β particles during decay
Can pass though paper, wood, and our bodies
Can mostly be stopped by several meters of concrete or several cm of lead
90Th230  86Ra He4 + 00

11. Nuclear Chemistry rev. 11/19/08
Figure: 21-T01

12. Nuclear Chemistry rev. 11/19/08
Figure: 21-T02

13. Nuclear Transformations
Nuclear Chemistry rev. 11/19/08
Nuclear Transformations
There are ~115 different elements, but more than different nuclei are known (Wait a minute—how is this possible?)
Only 264 nuclei are stable and do not decay over time
Stability of a nucleus depends on it neutron-to-proton ratio
The stable nuclei are in a region called the band of stability

14. The stable nuclei are located in the belt of stability (shaded )
As the at # increases, the 0n1:1p1 ratio of the stable nuclei increases
The stable nuclei are located in the belt of stability (shaded )
Radioactive nuclei occur outside this belt
2:1 neutron-to-proton ratio
Figure: 21-02
Nuclear Chemistry rev. 11/19/08

15. positron decay or electron capture
Nuclear Chemistry rev. 11/19/08
n/p too large => need more 1p1s &/or fewer 0n1s; so… turn 0n1s into 1p1s by…
n/p too large
beta decay X
n/p too small => need fewer 1p1s &/or more 0n1s; so… turn 1p1s into 0n1s by… Y
n/p too small
positron decay or electron capture

16. Nuclear Stability Certain numbers of 0n1s and 1p1s are extra stable
Nuclear Chemistry rev. 11/19/08
Certain numbers of 0n1s and 1p1s are extra stable
0n1 or 1p1 count = 2, 8, 20, 50, 82, 126
Like extra stable numbers of -1e0s in noble gases (2, 10, 18, 36, 54, 86)
Nuclei with even numbers of both 1p1s and 0n1s are more stable than those with odd numbers
All isotopes with at#s ≥ 84 (Po) are radioactive
All isotopes of 43Tc and 61Pm are radioactive

17. Transmutation Reactions
Nuclear Chemistry rev. 11/19/08
Transmutation Reactions
Transmutation - the conversion of an atom of one element into an atom of a different element
Can occur by radioactive decay
Can occur when particles (1p1-s, 0n1-s, or 2He4-s) bombard the nucleus of an atom
7 N H1  6C12 + 2He4
92U n1  93Np β0
4Be9 + 2He4  6C12 + 0n1

18. Nuclear Transmutation
Nuclear Chemistry rev. 11/19/08

19. Nuclear Chemistry rev. 11/19/08
Sample Exercise
What product is formed when radium-226 undergoes alpha decay?
What element undergoes alpha decay to form lead-208?
12Mg27 decays by beta emission to form…
1H3  __ + -1e0
3Li9  4Be9 + __

20. Sample Exercise 6C14  -1e0 + ____ 95Am241  2He4 + ____
Nuclear Chemistry rev. 11/19/08
Sample Exercise
6C14  -1e0 + ____
95Am241  2He4 + ____
7N16  6O16 + ____
Alpha decay of francium-208…
Beta emission by argon-37…
Positron emission by fluorine-17…

21. Sample Exercise 3Li6 + 0n1  2He4 + __
Nuclear Chemistry rev. 11/19/08
Sample Exercise
3Li6 + 0n1  2He4 + __
92U n1  __ + 56Ba n1
13Al27 + 2He4  __ + -1e0
92U235  38Sr90 + __ + 0n e0
83Bi214  2He4 + __
14Si27  -1e0 + __
29Cu66  30Zn66 + __

22. Nuclear Chemistry rev. 11/19/08
Decay Series
Figure: 21-04

23. Nuclear Chemistry rev. 11/19/08
Half-Life (t½)
The time required for one-half of the nuclei of a radioisotope sample to decay to products
After each half-life, one-half of the atoms we had at the beginning of the half-life have decayed into atoms of a new element

24. Nuclear Chemistry rev. 11/19/08

25. Nuclear Chemistry rev. 11/19/08
Fig. 23.3

26. Decay of a 10.0 g Sample of Sr-90
Nuclear Chemistry rev. 11/19/08
Decay of a 10.0 g Sample of Sr-90

27. Decay of a 1.000 mg Sample of Mo-99
Nuclear Chemistry rev. 11/19/08
Decay of a mg Sample of Mo-99

28. Brigham Young Researcher Scott Woodward Taking a Bone Sample
Nuclear Chemistry rev. 11/19/08
Brigham Young Researcher Scott Woodward Taking a Bone Sample

29. A Dendrochronologist Cutting a Section from a Dead Tree
Nuclear Chemistry rev. 11/19/08

30. Nuclear Chemistry rev. 11/19/08

31. Nuclear Chemistry rev. 11/19/08
Sample Exercise
Po-214 has a relatively short t½ of 164 sec. How many seconds would it take for 8.0 g of this isotope to decay to 0.25 g?
How many days does it take for 16 g of Pa-107 to decay to 1.0g? t½ of Pa-107 is 17 days.

32. Nuclear Chemistry rev. 11/19/08
Sample Exercise
In 5.49 seconds, 1.20 g of Ar-35 decay to leave only 0.15 g. What is t½ of Ar-35?
Na-24 has a t½ of 15 hours. How much Na-24 remains in an 18.0 g sample after 60 hours?

33. Sample Exercise
Nuclear Chemistry rev. 11/19/08
In 6.20 h, a 100. g sample of Ag-112 decays to g. What is t½ of Ag-112?
Mn-56 is a β emitter with t½ of 2.6 h. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 h?
C-14 emits beta radiation and decays with t½ of 5730 years. Assume you start with 2.00 x g C-14.
How long is 3 t½s?
How many grams of the isotope remain at the end of 3 t½s?

34. Nuclear Fission
Nuclear Chemistry rev. 11/19/08
Occurs when the nuclei of certain isotopes are bombarded with neutrons…
…and the nucleus splits into smaller fragments
In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons with will react with still more fissionable atoms
Can release enormous amounts of energy (atomic bombs, nuclear reactors)
Exothermic processes
Undergoes fission when struck by a slow-moving neutron
U-235 or Pu-239

35. Nuclear Chemistry rev. 11/19/08
Fig. 23.6

36. Fission
Nuclear Chemistry rev. 11/19/08

37. Uranium Oxide (refined uranium)
Nuclear Chemistry rev. 11/19/08

38. A PHYSICIST WORKS WITH A SMALL CYCLOTRON AT THE UNIVERSITY OF CALIFORNIA BERKLEY
Nuclear Chemistry rev. 11/19/08

39. Nuclear Chemistry rev. 11/19/08

40. An Aerial View of the Fermilab High Energy Particle Accelerator
Nuclear Chemistry rev. 11/19/08

41. The Accelerator Tunnel at Fermilab
Nuclear Chemistry rev. 11/19/08

42. Nuclear Chemistry rev. 11/19/08
Chain Reaction
If the fission process continues and the energy is unchecked, the result is a violent explosion
The sample of fissionable material must have a minimum ‘critical mass’ – if not, 0n1-s escape from the sample before they strike another nucleus and cause additional fission
The chain Rx stops if enough 0n1-s are lost

43. Nuclear Chemistry rev. 11/19/08
Critical Mass
The amount of fissionable material large enough to maintain the chain reaction with a constant rate of fission
When critical mass is present, only one 0n1 from each fission is subsequently effective in producing another fission

44. Nuclear Chemistry rev. 11/19/08
Figure: 21-16

45. Nuclear Chemistry rev. 11/19/08
(b)

46. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

47. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

48. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

49. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

50. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

51. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
(a)

52. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
Critical Mass
(a)
(b)

53. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
Critical Mass
(a)
(b)

54. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
Critical Mass
(a)
(b)

55. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
Critical Mass
(a)
(b)

56. Nuclear Chemistry rev. 11/19/08
Subcritical Mass
Critical Mass
(a)
(b)

57. Nuclear Chemistry rev. 11/19/08
Figure: 21-20C

58. Nuclear Chemistry rev. 11/19/08
Figure: 21-19

59. Reactant Core Coolant fluid Na(l) or H2O Moderator
Slows 0n1s so they can be absorbed (D2O, graphite)
Control Rods Decrease the # of slow moving 0n1s (B, Cd)
Nuclear Chemistry rev. 11/19/08

60. Shield Steam To steam turbine Shield Water Pump Control rod
Nuclear Chemistry rev. 11/19/08
Shield
Steam
To steam turbine
Shield
Water
Pump
Control rod
Uranium fuel

61. Nuclear Waste Fuel rods are one major source of waste
Nuclear Chemistry rev. 11/19/08
Fuel rods are one major source of waste
Fuel rods are made of fissionable isotope U-235 or Pu-239
Isotope-depleted (spent) fuel rods are removed and replaced with new fuel rods
All nuclear power plants have holding tanks, or “swimming pools,” for spent fuel rods
Water cools the spent rods, and acts as a radiation shield to reduce the radiation levels (12 m deep)
The rods continue to produce heat for years after their removal from the core
Spent fuel rods spend a decade or more in a holding tank

62. Annual Waste Production
Nuclear Fission
Nuclear Chemistry rev. 11/19/08
35,000 tons SO2
4.5 x 106 tons CO2
1,000 MW coal-fired
power plant
3.5 x 106
ft3 ash
Annual Waste Production
1,000 MW nuclear
power plant
70 ft3 vitrified waste

63. Nuclear Chemistry rev. 11/19/08
Fig. 23.p961bottom

64. Nuclear Fission
Nuclear Chemistry rev. 11/19/08
Hazards of the radioactivity in spent fuel compared to that of uranium ore

65. Nuclear Fusion Nuclei combine to produce a nucleus of greater mass
Nuclear Chemistry rev. 11/19/08
Nuclei combine to produce a nucleus of greater mass
Fusion Rxs release more energy than fission Rxs
Energy released by the sun comes from nuclear fission
Only occurs at high temperatures, over 40,000,000 °C
H nuclei (1p1s) fuse to make He nuclei (a combination of 2 low-mass nuclei to form a nucleus of larger mass)
1H2 + 1H3  2He4 + 0n1 + energy
More appealing because..
the greater availability of light isotopes
fusion products are generally not radioactive

66. Nuclear Chemistry rev. 11/19/08
Figure: 21-13

67. Nuclear Chemistry rev. 11/19/08
Detecting Radiation
Radiation cannot be heard, heard, felt, nor smelled…
…but, radiation produces ions, which can be detected by instruments…
… such as Geiger counters, scintillation counters, and film badges

68. Geiger Counter
Nuclear Chemistry rev. 11/19/08
Figure: 21-10

69. Geiger-Muller Counter
Nuclear Chemistry rev. 11/19/08
18–69
Geiger-Muller Counter

70. Geiger-Muller Counter
Nuclear Chemistry rev. 11/19/08
Geiger-Muller Counter

71. Scintillator
Nuclear Chemistry rev. 11/19/08

72. Nuclear Chemistry rev. 11/19/08
Film Badge

73. Using Radiation
Radioisotopes (tracers) are used in agriculture to test the effects of herbicides, pesticides, and fertilizers
Radioisotopes are used to diagnose medical problems and to treat diseases
Radiation (medical) in the body should…
have short t½
be quickly eliminated from the body
Nuclear Chemistry rev. 11/19/08

74. Household Smoke Detector
Contains a small amount of Am-241
When smoke particles interfere with ionizing O2 in the air, smoke gets ionized instead
The drop in current is detected by an electric circuit which sounds an alarm
Nuclear Chemistry rev. 11/19/08

75. Nuclear Chemistry rev. 11/19/08
Radiation in our Lives
Figure: 21-23

76. Dose-dependent Effects of Radiation
Nuclear Chemistry rev. 11/19/08
Dose-dependent Effects of Radiation

77. Nuclear Chemistry rev. 11/19/08

78. Radioisotopes in Medicine
Nuclear Chemistry rev. 11/19/08
Radioisotopes in Medicine
1 of 3 hospital patients has a nuclear medicine procedure
Na-24, t½ = 14.8 hr, b emitter, blood-flow tracer
I-131, t½ = 14.8 hr, b emitter, thyroid gland activity
I-123, t½ = 13.3 hr, g-ray emitter, brain imaging
F-18, t½ = 1.8 hr, b+ emitter, positron emission tomography
Tc-99m, t½ = 6 hr, g-ray emitter, imaging agent
Brain images with I-123-labeled compound

79. Chemistry In Action: Food Irradiation
Nuclear Chemistry rev. 11/19/08
Dosage
Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlic; inactivates trichinae in pork; kills or prevents insects from reproducing in grains, fruits, and vegetables
100 – 1000 kilorads
Delays spoilage of meat poultry and fish; reduces salmonella; extends shelf life of some fruit
1000 to 10,000 kilorads
Sterilizes meat, poultry and fish; kills insects and microorganisms in spices and seasoning.

80. Nuclear Chemistry rev. 11/19/08
Fig. 23.p969top

81. Image of a portion of the Cygnus Loop supernova remnant
Nuclear Chemistry rev. 11/19/08
Image of a portion of the Cygnus Loop supernova remnant

82. A pellet containing radioactive I-131
Nuclear Chemistry rev. 11/19/08

83. Nuclear Chemistry rev. 11/19/08

84. Effects of Short-Term Exposures to Radiation
Nuclear Chemistry rev. 11/19/08
Effects of Short-Term Exposures to Radiation

85. Nuclear Chemistry rev. 11/19/08
Typical radiation exposures for a person living in the United States (1 millirem = rem)

86. Nuclear Chemistry rev. 11/19/08
End