1. Nuclear Chemistry

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. 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

4. 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.

5. Nuclear reactions
“Normal” Chemical Reactions involve electrons, not protons and neutrons
Nuclear reactions involve the nucleus, release larger amounts of energy, and produce different elements.
The nucleus opens, and protons and neutrons are rearranged—more stable
Nucleons: are the protons and neutrons in the nucleus.
Nuclide: an atom

6. Binding Energy
Nuclear binding energy is the energy released when a nucleus is formed. It is also the amount of energy needed to break apart a nucleus. It is a measure of nucleus stability.
The higher the binding energy/nucleon, the more tightly the nucleons are held together.

7. Mass Defect
The mass defect is caused by the conversion of mass to energy when the nucleus is formed.
when protons + neutrons + electrons combine, the atom they form has less mass then the sum of the mass of the protons + neutrons + electrons. The difference is lost as energy

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

9. Calculate the mass defect
P 703 #4

10. Nuclear Stability
Band of stability:The neutron-proton ratio of stable nuclei cluster around a region when plotted.
The most stable nuclei have a 1:1 neutron:proton ratio.
As the # protons increases, the repulsive, electrostatic force between protons increases faster than nuclear force. Beyond Atomic #83, atoms are not stable.

11. Neutron-Proton Ratios
Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus.
A strong nuclear force helps keep the nucleus from flying apart.
Neutrons play a key role stabilizing the nucleus.
Therefore, the ratio of neutrons to protons is an important factor.

12. Nuclear stability: magic numbers
Even number nuclei tend to be stable. The nucleons that are most stable are 2,8,20,28,50,82,126 (either protons or neutrons)
They have completed nuclear energy levels.
Double magic He Pb

13. Stable Nuclei Nuclei above this belt have too many neutrons.
They tend to decay by emitting beta particles.

14. Stable Nuclei Nuclei below the belt have too many protons.
They tend to become more stable by positron emission or electron capture.

15. 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).

16. Types of Radiation Beta (β) – an electron
Alpha (ά) – a positively charged helium isotope
Beta (β) – an electron
Gamma (γ) – pure energy; called a ray rather than a particle

17. Other Nuclear Particles
Neutron emission
Positron emission – a positive electron (below band of stability)
Proton – usually referred to as hydrogen-1
Electron capture (rare) proton is converted to a neutron

18. Penetrating Ability

19. Balancing Nuclear Reactions
In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation)
Atomic numbers must balance
and
Mass numbers must balance
Use a particle or isotope to fill in the missing protons and neutrons

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

21. Nuclear Reactions
Alpha emission
Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.
Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

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

23. Nuclear Reactions
Beta emission
Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

24. Types of Radioactive Decay Gamma Emission
Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle) 

25. Types of Radioactive Decay Positron Emission
Loss of a positron (a particle that has the same mass as but opposite charge than an electron) e 1 C 11 6
 B 5 + e 1

26. Types of Radioactive Decay Electron Capture (K-Capture)
Addition of an electron to a proton in the nucleus
As a result, a proton is transformed into a neutron. p 1 + e −1
 n

27. Neutron Emission 87 Kr → 86Kr + 1 n 36 36 0
 a type of radioactive decay of atoms containing excess neutrons and a neutron is simply ejected from the nucleus

28. Other Types of Nuclear Reactions
Positron (0+1b): a positive electron
207
Electron capture: the capture of an electron

30. Practice
page 703 #11-13

32. 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.

33. 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

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

35. Nuclear Fission

36. 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. ___________ .

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

38. Band of Stability and Radioactive Decay

40. Representation of a fission process.

41. enrichment Natural uranium is a mixture of 0.7% U-235 and 99.3% U-238
Isotope separation is a physical process to concentrate or enrich 1 isotope relative to the other
Most reactors use require fuel rods that are 3% U-235
Nuclear weapons contain 90% U-235

42. 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.

43. Figure 19.6: Diagram of a nuclear power plant.

45. Nuclear power plant in Florida concerns

46. 5 components of a nuclear reactor
SHIELDING
CONTROL RODS MODERATOR
FUEL
COOLANT
Define Critical mass

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

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

49. Hydrogen bomb vs atomic bomb (thermonuclear bomb)

50. Chernobyl

51. PROS AND CONS OF NUCLEAR ENERGY
Pros: low cost, clean energy, provides stable load of energy (vs wind and solar), low pollution, higher energy density
Cons: not renewable (U has to be mined), nuclear waste, accidents, processing, mining and enrichment

52. 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.

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

54. 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

55. Learning Check!
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

56. Effects of Radiation

57. Geiger Counter
Used to detect radioactive substances

59. Radiocarbon Dating
Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14N + 1on ---> 14C + 1H The C-14 is oxidized to CO2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t1/2 = 5730 years. Activity of a sample can be used to date the sample.

60. Nuclear Medicine: Imaging
Thyroid imaging using Tc-99m

61. Food Irradiation
Food can be irradiated with g rays from 60Co or 137Cs.
Irradiated milk has a shelf life of 3 mo. without refrigeration.
USDA has approved irradiation of meats and eggs.