Nuclear+Stability

Graphs showing Z-N plots for stable and unstable nuclei can be found at http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/neutexc.html

The stable nuclei are plotted in our spreadsheet

Unstable nuclei decay by radioactive decay. (See http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html)

The three types of decay are: 1) Alpha Decay - a sort of fission into two lower mass nuclei 2) Beta Decay - a nucleon decay emitting either an electron or its antiparticle, the positron. 3) Gamma radiation - emmision of excess energy as a photon - because the energies involved are so large these are usually high energy photons or gamma rays.

The issue of whether a nucleus will decay can best be though by thinking about energy. Just like in chemistry reactions are most likely to proceed if the total energy before the reaction is less than the energy after so that the end state has less energy than the starting state.

Once a nuclear decay has occured it is possible that the resulting nuclei are also not stable. In this case they will often decay to another and another intermediate state until a final stable state is attained. This is called a decay series The more stable the state - the less liklihood of the nuclei decaying and hence the longer its half-life.