CP PHYSICS
NUCLEAR PHYSICS NOTES
Radioactive Decay
 neutrons add to nuclear attraction of protons in nucleus and keep protons from
flying apart
 elements with more than 83 protons – their extra neutrons cannot stabilize
nucleus
 lone neutron spontaneously decays into proton plus an electron (radioactive)
 3 types of radioactive decay:
1. Alpha
 helium nuclei
 positive charge
 slow
 easily stopped by paper
2. Beta
 stream of electrons
 negative charge
 results from neutron transforming into a proton
 faster moving
 stopped by sheet of aluminum
3. Gamma
 massless energy
 photons of EM radiation
 no charge
 high energy
 stopped by thick layer of lead
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
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
CP PHYSICS, NUCLEAR PHYSICS NOTES, page 2
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
 Examples:
1. Alpha Decay:
238
92
U 
4
2
He +
234
90
Th
2. Beta Decay:
234
90
Th 
0
-1
e +
234
91
Pa
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 a chain reaction – need critical mass (amount of mass for which each
fission event produces on average one additional fission event)
 subcritical – chain reaction dies out
 supercritical – chain reaction builds up explosively
 Energy production – use heat from reaction to boil water to produce steam to
turn a turbine and generate electricity
 Reactor has 3 components:
1) nuclear fuel (uranium) with a moderator (graphite, water) to slow down
neutrons
2) control rods – usually cadmium or boron, absorb neutrons, move in and
out of reactor to control reaction
3) water to transfer heat from reactor to generator
 Major drawback – radioactive waste products of fission, need special storage
casks
CP PHYSICS, NUCLEAR PHYSICS NOTES, page 3
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
o reaching high temps needed
o materials to confine fuel melt at high temps – need “nonmaterial”
containers, ex. magnetic field
 have achieved fusion in several devices but instabilities in plasma have prevented
sustained reactions
 currently energy costs to achieve reaction greater than energy yielded from the
reaction
 ideal
o does not require critical mass so cannot get out of control
o no air pollution – product is helium
o by-products not radioactive
o fuel is plentiful element in universe – Hydrogen
o amount of energy released will be virtually unlimited