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Nuclear Safeguards Education Portal

Particle and Electromagnetic Radiation

Decay of radionuclides results in the production of various forms of radiation. Radiation can occur as particles or as electromagnetic waves. Typical examples of particle radiation include alpha (α) particles, beta (β) particles, and neutrons. Alpha particles are energetic helium nuclei. They have a +2 charge and a mass of 4 amu. Beta particles are electrons. They can have either a -1 or +1 charge and have a very small mass. (β particles with a +1 charge are referred to as positrons.)

Electromagnetic radiation is composed of photons. Typical examples of this include x-rays and gamma-rays. X-rays are produced from transitions of electrons between electron orbitals. Gamma-rays are produced by transitions of nucleons in the nucleus.

Electromagnetic radiation is often broken down into two very broad classes: ionizing and non-ionizing.  The figure below shows the electromagnetic spectrum with these two broad classes defined.



The Electromagnetic Spectrum. Source: The US Environmental Protection Agency

Ionizing radiation is radiation composed of particles that individually carry enough kinetic energy to liberate an electron from an atom or molecule, thus ionizing it.  Examples of ionizing radiation include cosmic rays, alpha particles, beta particles, gamma rays, and x-rays. We will be focusing on ionizing radiation, since it is this type of radiation that is used in detecting nuclear material.

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