Beta Decay

Some nucleus are not stable if containing too many protons and neutrons.  Lightest elements prefer to have the same number of protons and neutrons.  Heavier elements prefer more neutrons than protons.  To redress the balance, proton and neutron can transform to one and other, releasing a electron or a positron so that charge is conserved.  The process of emitting electrons or positrons is called beta decay.  The process also emits neutrino so the energy level is also conserved.

Alpha Decay

Alpha particle contains 2 protons and 2 neutrons.  Radioactive material emits alpha particle and the process is called alpha decay.  In order to unfetter from the strong nuclear forces that holds the nucleon together, the alpha particle must attain sufficient energy to get pass the Coulomb barrier.  Alpha particle could not attain such energy.  They escapes from the nucleus using quantum tunneling.  Alpha particle's wave function has increasing probability to be found outside the nucleus as time goes by.  The wave function matches the observation of half life for radioactive substances