Radiation: Alpha, Beta & Gamma Decay

Radioactivity can be defined as the spontaneous emission of radiation from an atom having unstable nuclei or as a result of a nuclear reaction.

There are three types of radiation that are covered in this topic:

1. Alpha Decay(α)
2. Beta Decay(β)
3. Gamma Decay(γ)


Alpha Decay


An Alpha particle has the same mass number and atomic number as Helium and is said to be the same as the Helium-4 nucleus. Usually most heavy elements emit alpha particles. When an atom undergoes this form of decay its mass number will decrease by 4 while its atomic number decreases by 2.

For example:

Beta Decay

• Electron Emission: - As the term suggests, this is when an electron gets emitted from the nucleus, this usually results in the charge in the nucleus increasing by one.

An example of how to calculate Beta Decay is given below:

Gamma Decay


This usually occurs after alpha decay has taken place. This is as a result of the excess energy produced by the alpha particle; this energy is released when the gamma-ray is emitted from the nucleus. Usually no chemical change occurs when an atom emits gamma-ray because it has neither charge nor mass. Gamma-rays are also delayed, short-lived and metastable (m).

Example: