1. Nuclear Chemistry
Chapter 23

2. Radioactivity
One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).
She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

3. Nuclear Reactions vs. Normal Chemical Changes
Nuclear reactions involve the nucleus
The nucleus opens, and protons and neutrons are rearranged
The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy
“Normal” Chemical Reactions involve electrons, not protons and neutrons

4. 23.1

5. Types of Radiation Beta (β) – an electron
Alpha (ά) – a positively charged (+2) helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons
Beta (β) – an electron
Gamma (γ) – pure energy; called a ray rather than a particle

6. Other Nuclear Particles
Neutron
Positron – a positive electron
Proton – usually referred to as hydrogen-1
Any other elemental isotope

7. Penetrating Ability

8. Geiger-Müller Counter
23.7

9. Geiger Counter
Used to detect radioactive substances

10. X Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number X A Z
Element Symbol
Atomic Number 1p 1 1H or
proton 1n
neutron 0e -1 0b or
electron 0e +1 0b or
positron
4He 2 4a or
a particle A 1 1 4 Z 1 -1 +1 2
23.1

11. Balancing Nuclear Equations
Conserve mass number (A).
The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 1n U
235 92 + Cs
138 55 Rb 96 37
+ 2
= x1
Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 1n U
235 92 + Cs
138 55 Rb 96 37
+ 2
= x0
23.1

12. 212Po decays by alpha emission
212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.
4He 2 4a or
alpha particle -
212Po He + AX 84 2 Z
212 = 4 + A
A = 208
84 = 2 + Z
Z = 82
212Po He + 208Pb 84 2 82
23.1

13. Nuclear Stability and Radioactive Decay
Beta decay
14C N + 0b + n 6 7 -1
Decrease # of neutrons by 1
40K Ca + 0b + n 19 20 -1
Increase # of protons by 1
1n p + 0b + n 1 -1
Positron decay
11C B + 0b + n 6 5 +1
Increase # of neutrons by 1
38K Ar + 0b + n 19 18 +1
Decrease # of protons by 1
1p n + 0b + n 1 +1
n and n have A = 0 and Z = 0
23.2

14. Nuclear Stability and Radioactive Decay
Electron capture decay
37Ar + 0e Cl + n 18 17 -1
Increase # of neutrons by 1
55Fe + 0e Mn + n 26 25 -1
Decrease # of protons by 1
1p + 0e n + n 1 -1
Alpha decay
Decrease # of neutrons by 2
212Po He + 208Pb 84 2 82
Decrease # of protons by 2
Spontaneous fission
252Cf In + 21n 98 49
23.2

15. Learning Check
What radioactive isotope is produced in the following bombardment of boron?
10B He ? n

16. Learning Check
What radioactive isotope is produced in the following bombardment of boron?
10B He N n

17. Write Nuclear Equations!
Write the nuclear equation for the beta emitter Co-60.
60Co 0e + 60Ni

18. Artificial Nuclear Reactions
New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B.
Reactions using neutrons are called g reactions because a g ray is usually emitted.
Radioisotopes used in medicine are often made by g reactions.

19. Artificial Nuclear Reactions
Example of a g reaction is production of radioactive 31P for use in studies of P uptake in the body.
3115P n ---> 3215P + g

20. Transuranium Elements
Elements beyond 92 (transuranium) made starting with an g reaction
23892U n ---> U + g
23992U > Np b
23993Np ---> Pu b

21. Nuclear Stability
Certain numbers of neutrons and protons are extra stable
n or p = 2, 8, 20, 50, 82 and 126
Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)
Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
All isotopes of the elements with atomic numbers higher than 83 are radioactive
All isotopes of Tc and Pm are radioactive
23.2

22. Band of Stability and Radioactive Decay

23. Stability of Nuclei Out of > 300 stable isotopes: N Even Odd Z 15752
3115P
Even
Odd 50 5
21H, 63Li, 105B, 147N, 18073Ta
199F

24. Half-Life
HALF-LIFE is the time that it takes for 1/2 a sample to decompose.
The rate of a nuclear transformation depends only on the “reactant” concentration.

25. Half-Life
Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?

26. Kinetics of Radioactive Decay
For each duration (half-life), one half of the substance decomposes.
For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5 grams
After 10.8 days > 6.25 grams

27. Kinetics of Radioactive Decay
N daughter
rate = - DN Dt
rate = lN DN Dt
= lN -
N = N0e(-lt)
lnN = lnN0 - lt
N = the number of atoms at time t
N0 = the number of atoms at time t = 0
l is the decay constant (sometimes called k)
Ln 2 = t½ l
k =
23.3

28. Kinetics of Radioactive Decay
[N] = [N]0exp(-lt)
ln[N] = ln[N]0 - lt
[N]
ln [N]
23.3

29. Radiocarbon Dating 14N + 1n 14C + 1H 14C 14N + 0b + n t½ = 5730 years6
14C N + 0b + n 6 7 -1
t½ = 5730 years
Uranium-238 Dating
238U Pb + 8 4a + 6 0b 92 -1 82 2
t½ = 4.51 x 109 years
23.3

30. Learning Check!
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?

31. Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q
Quality Factor
g-ray = 1
b = 1
a = 20
23.8

32. Effects of Radiation

33. Nuclear Fission Fission is the splitting of atoms
These are usually very large, so that they are not as stable
Fission chain has three general steps:
1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron)
2. Propagation. 236U fission releases neutrons that initiate other fissions
3. Termination.

34. Nuclear Fission

35. Nuclear Fission 235U + 1n 90Sr + 143Xe + 31n + Energy92 54 38
Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2
Energy = 3.3 x 10-11J per 235U
= 2.0 x 1013 J per mole 235U
Combustion of 1 ton of coal = 5 x 107 J
23.5

36. Representation of a fission process.

37. Mass Defect Some of the mass can be converted into energy
Shown by a very famous equation!
E=mc2
Energy
Mass
Speed of light

38. BE = 9 x (p mass) + 10 x (n mass) – 19F mass
Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.
BE + 19F p + 101n 9 1
E = mc2
BE = 9 x (p mass) + 10 x (n mass) – 19F mass
BE (amu) = 9 x x –
BE = amu
1 amu = 1.49 x J
BE = 2.37 x 10-11J
binding energy per nucleon =
binding energy
number of nucleons =
2.37 x J
19 nucleons
= 1.25 x J
23.2

39. Nuclear binding energy per nucleon vs Mass number
nuclear stability
23.2

40. Nuclear Fission
Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.
The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.
Non-critical
Critical
23.5

41. Nuclear Fission & POWER
Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.
17% of the world’s energy comes from nuclear.

42. Diagram of a nuclear power plant

43. Annual Waste Production
Nuclear Fission
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
23.5

44. Hazards of the radioactivities in spent fuel compared to uranium ore
Nuclear Fission
Hazards of the radioactivities in spent fuel compared to uranium ore
23.5
From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG

45. Chemistry In Action: Nature’s Own Fission Reactor
Natural Uranium
% U % U-238
Measured at Oklo
% U-235

46. Fusion Nuclear Fusion small nuclei combine 2H + 3H 4He + 1n + 1 1 2 0
Occurs in the sun and other stars
Energy

47. Tokamak magnetic plasma confinement
Nuclear Fusion
Fusion Reaction
Energy Released
2H + 2H H + 1H 1
6.3 x J
2H + 3H He + 1n 1 2
2.8 x J
3.6 x J
6Li + 2H He 3 1 2
Tokamak magnetic plasma confinement
23.6

48. Nuclear Fusion
Fusion
Excessive heat can not be contained
Attempts at “cold” fusion have FAILED.
“Hot” fusion is difficult to contain

49. Radioisotopes in Medicine
1 out of every 3 hospital patients will undergo a nuclear medicine procedure
24Na, t½ = 14.8 hr, b emitter, blood-flow tracer
131I, t½ = 14.8 hr, b emitter, thyroid gland activity
123I, t½ = 13.3 hr, g-ray emitter, brain imaging
18F, t½ = 1.8 hr, b+ emitter, positron emission tomography
99mTc, t½ = 6 hr, g-ray emitter, imaging agent
Brain images with 123I-labeled compound
23.7

50. Chemistry In Action: Food Irradiation
Dosage
Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlics. 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.