1. Nuclear Physics Notes
CP Physics
Ms. Morrison

2. Radioactive Decay
Elements with more than 83 protons – extra neutrons cannot stabilize nucleus
Lone neutron spontaneously decays into a proton plus an electron (radioactive)
Three types of Radioactive Decay
Alpha
Beta
Gamma

3. Alpha Decay
Helium nuclei
Positive charge
Slow
Easily stopped by paper

4. Beta Decay Stream of high speed electrons Negative charge
Results from neutron transforming into a proton
Faster moving
Stopped by sheet of aluminum

5. Gamma Decay Massless energy Photons of EM radiation No charge
High energy
Stopped by thick layer of lead (or several feet of concrete)

6. Radioactive Isotopes
Isotope = atom of an element that has a different number of neutrons
All isotopes of an element are chemically identical
All elements have isotopes
Some isotopes are radioactive and unstable – they will undergo spontaneous radioactive decay

7. Radioactive Half-life
Isotopes decay at different rates
Half-life = time needed for half of radioactive atoms to decay
Decay rates are constant
To calculate amount of sample left: (1/2)n where n = number of half-lives

8. Nuclear Equations Show alpha or beta decay
Transmutation: one element changes into another element through radioactive decay
Mass numbers and atomic numbers on each side of the equation must be equal
Example of alpha decay:
238 U  4 He Th
Example: beta decay:
234 Th  0 e Pa

9. Nuclear Fission Splitting of atomic nuclei
Absorbing a neutron causes nucleus to elongate and deform and then split
Releases huge amounts of energy
When nucleus splits – releases neutrons which can be absorbed by other nuclei causing them to split  chain reaction
To sustain chain reaction need critical mass (amount of mass for which each fission event produces an average of one additional fission event)
Subcritical – chain reaction dies out
Supercritical – chain reaction builds up explosively

10. Nuclear Fission, pg 2
Energy production – use heat from reaction to boil water to produce steam to turn a turbine and generate electricity
Reactor has 3 components:
Nuclear fuel (uranium) with moderator (graphite, water) to slow down neutrons
Control rods – usually cadmium or boron, absorb neutrons, move in and out of reactor to control reaction
Water to transfer heat from reactor to generator
Major drawback – radioactive waste products of fission, need special storage casks

11. Nuclear Fusion Opposite of nuclear fission
Energy released by light nuclei fusing
Requires very high speeds for nuclei to collide and fuse
Associated with high temps – thermonuclear fusion (welding together of atomic nuclei by high temp)
Difficulties in using for energy production
Reaching high temps needed
Materials to confine fuel melt at high temps – need “nonmaterial” containers, ex. Magnetic field

12. Nuclear Fusion, pg 2
Have achieved fusion in several devices but instabilities in plasma have prevented sustained reactions
Currently energy costs to achieve reaction greater than energy yield from the reaction
Ideal
Does not require critical mass so cannot get out of control
No air pollution – product is helium
By-products not radioactive
Fuel is plentiful element in universe – Hydrogen
Amount of energy released will be virtually unlimited