1. Nuclear Chemistry
Chapter 21

2. Nuclear Reactions
Some nuclei are unstable. They are said to be radioactive and emit particles and usually high-energy electromagnetic radiation (gamma rays) at the same time.
Other nuclear reactions involve bombarding nuclei with particles such as neutrons, protons, alpha particles or other nuclei. (particle accelerators)

3. Homework problems
pages
1, 3-11, 14-18, 20, 23-25, 28, 29, 33, 34, 36-46, 51, 52, 60, 64, 66, 68, 71

4. 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

5. 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

6. 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

7. 23.1

8. 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

9. 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

10. Example 21.1
Write balanced nuclear equations for the
Decay of U-238 to Th-234
Decay of Cs-137 to Ba-137
Emission of a beta particle by As-78

11. positron decay or electron capture
n/p too large
beta decay X Y
n/p too small
positron decay or electron capture
23.2

12. 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

13. 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
Δ E = (Δ m)c2
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

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

15. Ex 21. 2 The atomic mass of I-127 is 126. 9004 amu
Ex 21.2 The atomic mass of I-127 is amu. Calculate the nuclear binding energy and the BE per nucleon.
c = 3.00 x 108m/s
1 kg = 6.02 x 1026 amu
1 J = 1 kg m2/s2

16. Natural Radioactivity
Nuclei outside the belt of stability or with more than 83 protons are unstable and decay naturally.
This decay obeys 1st order kinetics and therefore has a constant half-life.

17. Kinetics of Radioactive Decay
N daughter
rate = - DN Dt
rate = lN DN Dt
= lN -
N = N0exp(-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
ln2 = t½ l
23.3

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

20. Final Exam – June 17 EH Assignment Due June 15 Unit 23 Mininum score
Sec 1 Properties of Radiation 90
Sec 2 Balancing Nuclear Reactions
Sec 3 Predicting Nuclear Stability
Sec 4 Radiation Decay Kinetics
Sec 5 Radiation Measurement
Sec 6 Nuclear Binding Energy
Final Exam – June 17

21. Radiocarbon Dating 14N + 1n 14C + 1H 14C 14N + 0b + n t½ = 5730 years6
14C N + 0b + n 6 7 -1
t½ = 5730 years
The C-14 isotope is produced in the upper atmosphere N-14 through the action of cosmic rays. All living organisms contain C-14, but when the organism dies the amount of C-14 decreases.
Paper from the Dead Sea Scrolls was found to have only times as much C-14 as that of a living plant. What is the age of the scroll?
23.3

22. K-40 decays to Ar-40 with a half life of 1.2 x 109 years.
Age of Rocks
K-40 decays to Ar-40 with a half life of 1.2 x 109 years.
Uranium-238 Dating
238U Pb + 8 4a + 6 0b 92 -1 82 2
t½ = 4.51 x 109 years
23.3

23. Nuclear Transmutations
In 1919 Rutherford bombarded N with alpha particles and produced O-17. This was the first manmade nuclear reaction.
Why not just mix N and He?
Example 21.3
Neutrons are particularly useful in producing synthetic isotopes since they have no charge.

24. Nuclear Transmutation
Cyclotron Particle Accelerator
14N + 4a O + 1p 7 2 8 1
27Al + 4a P + 1n 13 2 15
14N + 1p C + 4a 7 1 6 2
23.4

25. Nuclear Transmutation
23.4

26. A new type of nuclear reaction – fission- was discovered in 1938
A new type of nuclear reaction – fission- was discovered in The experiments were carried out in Germany by Hahn and Strassman and interpreted by Lisa Meitner.
U-235 and Pu-239 will undergo fission when bombarded with neutrons.
U-235 makes up 0.7% of natural uranium and Pu-239 can be produced from the more abundant U-238.

27. 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

28. Representative fission reaction
Nuclear Fission
Representative fission reaction
235U + 1n Sr + 143Xe + 31n + Energy 92 54 38
23.5

29. Notice that the fission products are not the normal isotopes and are always highly radioactive. This is true of fission bombs and nuclear reactors.

30. 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

31. The little boy bomb. It used U-235

32. The fat man bomb. It used Pu-239

33. Fig. 21.9

34. Schematic diagram of a nuclear fission reactor
Much of the heat comes
from decay of fission
products. Even if
fission stops, this
decay does not.
23.5

35. 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

36. 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

37. 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
High T required.
Why?
Tokamak magnetic plasma confinement
23.6

38. Thermonuclear bombs
Mark 17 model

39. 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
23.6

40. Geiger-Müller Counter
23.6

41. 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
23.6

42. The Standard Model is the name give to the current theory of fundamental particles and how they interact.

43. There are four fundamental forces in nature.
Electromagnetic force
Gravity
Strong nuclear force
Weak nuclear force
Electroweak Theory has shown that 1 and 4 are really different aspects of the same force.

44. There are 12 fundamental fermion particles in nature
There are 12 fundamental fermion particles in nature. (spin =1/2, 3/2, 5/2, …
6 flavors of quarks and 6 flavors of leptons. All the matter that we are familiar with are made up of two quarks – up and down and one lepton – the electron.

45. The other category of particles are the bosons (spin =0, 1, 2,…)
The bosons are force carriers. For example, the electromagnetic force is caused by an exchange of photons.
Each force has one or more force carriers.

46. The strong nuclear force is carried by gluons
The strong nuclear force is carried by gluons. Quarks come in three colors – red, green and blue. This is analogous to + and – for the electromagnetic force.
Unlike colors attract. This force is also called the color force.

48. Fermilab
Ring is 4 miles around.
Protons and antiprotons
collide.

49. Fermilab – particle tracks in detector.
Discovery of top quark.

50. Practice Test #

51. and Ca-45, c. Mo-95, Tc-92 d. Hg-195, Hg-196