Apha Emission

Alpha particles were the first particles of radiation that were discovered (that's why they are called alpha - A in the Greek alphabet). These were also the particles that were used by Rutherford to find the nucleus of the atom.
An example of a typical alpha emission reaction would be the decomposition of ²²²Rn.

 

Some alpha emission reactions can also involve other particles as well. For instance, one of the reactions that ²³⁵U can undergo involves the absorbtion of a neutron prior to decomposition and then the release of 3 neutrons (as well as the alpha particle).

The emission of the 3 extra neutrons is incredibly important, since those 3 neutrons can hit the nuclei of three other U atoms and cause them to decompose. This ever-expanding process is called a chain reaction, and is the basis for both nuclear power and nuclear bombs.