Alpha, beta and gamma radiation

An unstable atomic nucleus can emit radiation spontaneously: no external trigger is needed. The direction in which the radiation is emitted is random.

The three types of radiation differ in what they consist of:

• Alpha radiation consists of alpha particles. Each alpha particle is a helium nucleus containing two protons and two neutrons. It has a charge of $$+2e$$.
• Beta-minus radiation consists of high-speed electrons emitted from the nucleus. Each beta-minus particle has a charge of $$-e$$.
• Gamma radiation consists of high-energy electromagnetic photons. Gamma photons have no electric charge and no rest mass.

Here, $$e$$ is the magnitude of the charge on a proton or an electron.

Ionising and penetrating effects

Radiation is ionising if it can remove electrons from atoms or molecules. Alpha radiation has the strongest ionising effect, beta radiation is intermediate, and gamma radiation has the weakest ionising effect.

Their relative penetrating abilities follow the opposite order: alpha is the least penetrating, beta is intermediate, and gamma is the most penetrating. An alpha particle loses energy rapidly as it ionises matter, so it travels only a short distance through it. Gamma radiation produces less ionisation and generally penetrates further through matter.