1. Nuclear Chemistry and Nuclear Physics
Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
Nuclear Chemistry and Nuclear Physics
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.

2. The Nucleus
Remember that the nucleus is comprised of the two nucleons, protons and neutrons.
The number of protons is the atomic number.
The number of protons and neutrons together is effectively the mass of the atom.

3. Isotopes
Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms.
There are three naturally occurring isotopes of uranium:
Uranium-234
Uranium-235
Uranium-238

5. Radioactivity
It is not uncommon for some nuclides of an element to be unstable, or radioactive.
We refer to these as radionuclides.
There are several ways radionuclides can decay into a different nuclide.

6. Types of Radioactive Decay

8. SeparationAlphaBetaGamma.MOV Separation of Radiation

12. Nuclear Reactions
The chemical properties of the nucleus are independent of the state of chemical combination of the atom.
In writing nuclear equations we are not concerned with the chemical form of the atom in which the nucleus resides.
It makes no difference if the atom is as an element or a compound.
Mass and charges MUST BE BALANCED!!!

13. He U Th He Alpha Decay: Loss of an -particle (a helium nucleus) + 4 2
238 92
 Th
234 90 He 4 2 +

14. Alpha Decay Mass changes by 4
The remaining fragment has 2 less protons
Alpha radiation is the less penetrating of all the nuclear radiation (it is the most massive one!)

15.  e I Xe e Beta Decay: Loss of a -particle (a high energy electron) +−1 e or I
131 53 Xe 54
 + e −1

16. Beta Decay
Involves the conversion of a neutron in the nucleus into a proton and an electron.
Beta radiation has high energies, can travel up to 300 cm in air.
Can penetrate the skin

17. Beta decay
Write the reaction of decay for C-14

18. Gamma Emission:
Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle) 

19. e + C B e Positron Emission:
Loss of a positron ( particle with same mass, but opposite charge than an electron)
e + 1 C 11 6
 B 5 + e 1

20. Positron emission
Involves the conversion of a proton to a neutron emitting a positron.
The atomic number decreases by one, mass number remains the same.

21. Electron Capture (K-Capture)
Capture by the nucleus of an electron from the electron cloud surrounding the nucleus.
As a result, a proton is transformed into a neutron. p 1 + e −1
 n

22. Rb Kr Electron capture Rb-81
Note that the electron goes in the side of the reactants. Electron gets consumed. Rb 81 37  Kr 36

23. Patterns of nuclear Stability
Any element with more than one proton ( all but hydrogen) will have repulsions between the protons in the nucleus.
A strong nuclear force helps keep the nucleus from flying apart.

24. Neutron-Proton Ratios
Neutrons play a key role stabilizing the nucleus.
The ratio of neutrons to protons is key to determine the stability of a nucleus .

25. Neutron-Proton Ratios
As nuclei get larger, it takes a greater number of neutrons to stabilize the nucleus.

26. Neutron-Proton Ratios
For smaller nuclei (Z  20) stable nuclei have a neutron-to-proton ratio close to 1:1.

27. Stable Nuclei
The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.

28. Stable Nuclei Nuclei above this belt have too many neutrons.
They tend to decay by emitting beta particles. ( neutron becomes proton )

29. Above the belt of stability Beta particle emission
Too many neutrons. The nucleus emits Beta particles, decreasing the neutrons and increasing the number of protons.

30. Stable Nuclei Nuclei below the belt have too many protons.
They tend to become more stable by positron emission or electron capture (both lower the number of protons)

31. Stable Nuclei
Elements with low atomic number are stable if # proton = # neutrons
There are no stable nuclei with an atomic number greater than 83.
These nuclei tend to decay by alpha emission.

32. Below the stability belt Increase the number of neutrons (by decreasing # protons)
Positron emission more common in lighter nuclei.
Electron capture common for heavier nuclei.

34. Radioactive Series
Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.
They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

35. Predicting modes of nuclear decay
Xe-118
Pu-239
In-120

36. beta decay
Positron emission or electron capture
Alpha decay (too heavy, loses mass)
Beta decay (ratio too low, gains protons)

37. MAGIC NUMBERS 2, 8, 20, 28, 50, or 82
Nuclei with 2, 8, 20, 28, 50, or 82 protons or 2, 8, 20, 28, 50, 82, or 126 neutrons tend to be more stable than nuclides with a different number of nucleons.

38. Some Trends
Nuclei with an even number of protons and neutrons tend to be more stable than nuclides that have odd numbers of these nucleons.

39. Shell model of the nucleus
Nucleons are described a residing in shells like the shells for electrons.
The numbers 2,8,18,36,54,86 correspond to closed shells in nuclei.
Evidence suggests that pair of protons and pairs of neutrons have special stability

40. Transmutations To change one element into another.
Only possible in nuclear reactions never in a chemical reaction.
In order to modify the nucleus huge amount of energy are involved.
These reactions are carried in particle accelerators or in nuclear reactors

41. Nuclear transmutations
Alpha particles have to move very fast to overcame electrostatic repulsions between them and the nucleus.
Particle accelerators or smashers are used. They use magnetic fields to accelerate the particles.

42. Particle Accelerators (only for charged particles!)
These particle accelerators are enormous, having circular tracks with radii that are miles long.

43. Cyclotron
Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide.

44. Neutrons
Can not be accelerated. They do not need it either (no charge!).
Neutrons are products of natural decay, natural radioactive materials or are expelled of an artificial transmutation.
Some neutron capture reactions are carried out in nuclear reactors where nuclei can be bombarded with neutrons.

45. Representing artificial nuclear transmutations
14N + 4He  7O + 1H
Target nucleus ( bombarding particle, ejected particle ) product nucleus
14N (a, p) 17O
Write the balanced nuclear equations summarized as followed:
16 O ( p, a) N
27Al (n, a)24 Na

46. Measuring Radioactivity
One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample.
The ionizing radiation creates ions, which conduct a current that is detected by the instrument.

48. CERN
Left Page Reading
On another left page: “What have we learned from CERN?”

50. Left Page Activity
Split your page into three horizontal sections: “Antimatter”, “Higgs Boson Particle” and “Large Hadron Collider”
In each section you are going to research what it is and why it is important.

51. Mass defect
The mass of the nucleus is always smaller than the masses of the individual particles added up.
The difference is the mass defect.
That small amount translate to huge amounts of energy E = (m) c2
That energy is the Binding energy of the nucleus, and is the energy needed to separate the nucleus.

52. Energy in Nuclear Reactions
For example, the mass change for the decay of 1 mol of uranium-238 is − g.
The change in energy, E, is then
E = (m) c2
E = (−4.6  10−6 kg)(3.00  108 m/s)2
E = −4.1  1011 J This amount is 50,000 times greater than the combustion of 1 mol of CH4

53. Types of nuclear reactions fission and fusion
The larger the binding energies, the more stable the nucleus is toward decomposition.
Heavy nuclei gain stability (and give off energy) if they are fragmented into smaller nuclei. (FISSION)

54. Even greater amounts of energy are released if very light nuclei are combined or fused together. (FUSION)

55. Nuclear Fission How does one tap all that energy?
Nuclear fission is the type of reaction carried out in nuclear reactors.

56. Nuclear Fission
Bombardment of the radioactive nuclide with a neutron starts the process.
Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.

57. Nuclear Fission
This process continues in what we call a nuclear chain reaction.

58. Nuclear Fission
If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.

59. Nuclear Fission
Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.

60. Controlled vs Uncontrolled nuclear reaction
Controlled reactions: inside a nuclear power plant
Uncontrolled reaction: nuclear bomb

61. Nuclear Reactors
In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

62. Nuclear Reactors
The reaction is kept in check by the use of control rods.
These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.

64. FUSION Combining small nucleii to form a larger one.
Require millions of K of temperature

65. Fusion 1H + 1H  2H + 1e + energy 1H + 2H  3He + energy
3He + 3He  4He + 21H + energy
Reaction that occurs in the sun
Temperature 107 K
Heavier elements are synthesized in hotter stars 108 K using Carbon as fuel

66. Nuclear Fusion Fusion would be a superior method of generating power.
The good news is that the products of the reaction are not radioactive.
The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.

67. Nuclear Fusion (thermonuclear reactions)
Tokamak apparati like the one shown at the right show promise for carrying out these reactions.
They use magnetic fields to heat the material.
3 million K degrees were reached inside but is not enough to begin fusion which requires 40 million K

69. Rates of radioactive decay rate = k N N is the number of radioactive nuclei
Activity: rate at which a sample decays. Expressed in disintegrations per unit time.
Becquerel (Bq) SI unit : one nuclear disintegration per second.
Curie (Ci) 3.7x1010 disintegrations per second, the rate of decay of 1g of Ra

70. RADIOACTIVE DECAY
As a radioactive sample decays, the amount of radiation emanating for the sample decays as well.
After one half life, half of the emanations!

71. Half-Life
Half-life is defined as the time required for one-half of a reactant to react. .

72. Half life
The half life of a reaction is useful to describe how fast it occurs.
For a first order reaction (like nuclear decay!) it does not depend on the initial concentration of the reactants.
HALF LIFE IS CONSTANT FOR A FIRST ORDER REACTION

73. Half Life Decay of 10.0 g sample of Sr-90 t1/2= 28.8 y

74. Problem 1 The half life of 210Pb= 25 y
1) How much left of a sample of 50 mg will remain after 100 y?
2) Find number of half lives
3) Find fraction left

75. g
half lives
3- 1/16

76. Problem 2 How many years will take for 50mg of 210Pb to decay to 5 mg?
Half life of 210Pb= 25 y

77. 83 years

78. Problem 3
90 % of a radioisotope disintegrates in 36 hs. What is the half life?

79. Problem 4 .953 g of Sr-90 remains after 2 y from a 1.000g sample.
.953 g of Sr-90 remains after 2 y from a 1.000g sample.
a) find the half life
b) how much will remain after 5 y?

80. Half life = 28.8 years
Amount left (No) = 0.89 g

81. Radioactive Dating
A rock contains .257 mg of Pb-206 for every mg of U-238.
T1/2 = 4.5 x 10 9 y
How old is the rock?

82. No = we will assume that all the Pb-206 that is now present will come from the original U, plus the U that is still present
(check the answer in textbook!)

83. Calculating half life:
If 87.5 % of a sample of I-131 decays in 24 days, what is the half life of the
I-131?