Radioactivity is the process in which unstable atomic nuclei spontaneously decompose to form nuclei with a higher stability by the release of energetic sub atomic particles.

The above definition tells us that radioactivity is a random or spontaneous naturally occurring process.  The process cannot be influenced by external factors such as heat, pressure or exposure to a magnetic field. This is not to be confused with the radiation that arises from nuclear fission in nuclear power stations. Here the fission is not spontaneous but is triggered in a nuclear reactor by the bombardment of high energy neutrons. Secondly, it occurs in unstable atoms or more accurately unstable isotopes called radioisotopes. These atoms are unstable because of the unbalanced nuclear forces within their nuclei.

The sub atomic particles and their associated energy that are released during the decomposition of the unstable nuclei are referred to as radiation.



There are 3 main types of radiations.

  • Alpha particles
  • Beta particles
  • Gamma rays

The animation below shows the three types of radiations that can be released when an unstable nucleus decays.

Alpha particles are released by high mass, proton rich unstable nuclei. The alpha particle is a helium nucleus; it consists of two protons and two neutrons. It contains no electrons to balance the two positively charged protons. Alpha particles are therefore positively charged particles moving at high speeds.

Beta particles are emitted by neutron rich unstable nuclei. Beta particles are high energy electrons. These electrons are not electrons from the electron shells around the nucleus, but are generated when a neutron in the nucleus splits to form a proton and an accompanying electron. Beta particles are negatively charged.

Gamma rays are electromagnetic waves of very short wavelength and high frequency. Gamma rays are emitted by most radioactive sources along with alpha or beta particles. After alpha or beta emission the remaining nucleus may still be in an excited energy state. By releasing a gamma photon it reduces to a lower energy state. Gamma rays have no electrical charge associated with them.