If all of the isotopes are plotted on a chart we find that there is a general trend for those that are stable and those that are unstable lie outside the zone of nuclear stability (rather like a 'line of best fit')

The graph below shows the type of emitters for each unstable nuclide - you can see that there is a pattern of behaviour linked to which side of the stability line they are located. They decay to become more stable - closer to that line!

proton rich nuclides with low mass tend to be positron emitters

neutron rich nuclides tend to be beta emitters

proton rich heavy nuclides tend to be alpha emitters

and

gamma radiation is often found to accompany or follow emission of radiation of the other types as the particles in the nucleus rearrange themselves to a more stable state after the emission of the 'matter' or 'antimatter' nuclear radiation.