Nuclear reactions are accompanied by energy changes that are much, much bigger than the energy changes of chemical reactions.
Unstable atomic nuclei that decompose spontaneously give off radiation in the form of high-speed particles and/or light energy. This decay process is called radioactivity.
The spontaneous release of radioactivity takes one or more of three forms:
An α-particle is the nucleus of a helium atom (two protons and two neutrons). It has a mass of 4 amu's and a charge of +2.