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Basic facts about radiation

Atoms

Everything is made up from atoms. Each atom contains a nucleus, consisting of protons and neutrons, around which orbit electrons.

All atoms of the same chemical element have the same number of protons.

They can, however, have different number of neutrons, when they do they are called isotopes of the element. Hydrogen, for instance, has 3 isotopes: hydrogen, deuterium and tritium.

Atoms are often identified by the name of the element and the number of protons and neutrons in the nucleus, eg, lithium-7, which has 3 protons and 4 neutrons. When described with this precision the atoms are often referred to as nuclides.

Atoms of the same or different elements combine to form molecules, eg, water.

Radioactivity and radiation

Many atoms are unstable and can spontaneously change into atoms of another element when they emit radiation. This property is called radioactivity and the change is called decay; the unstable atom is said to be a radionuclide. For instance, carbon-14 is a radionuclide that decays to nitrogen-14, a stable nuclide.

The radiations most commonly emitted by radionuclides are alpha particles, beta particles and gamma rays.

Alpha particles consist of 2 protons and 2 neutrons bound together; they are relatively heavy and have 2 positive charges.

Beta particles are electrons created by changes of neutrons into protons in the nucleus of radionuclides.

Gamma rays can be considered to be packets of energy, like light.

X-rays are similar to Gamma rays, but of lower energy so they are less penetrating through materials.

X-rays are usually produced by bombarding a metal target with electrons in a vacuum.

Radiation and tissue

Radiation can interact with the electrons in surrounding molecules producing changes such as ionisation. Ionised water molecules change to ‘free radicals’, which are highly reactive in a chemical sense, and which can alter important molecules in tissue.

They can produce chemical changes in DNA, the basic material which controls the structure and function of the cells that make up our bodies. Radiation can also ionise DNA molecules directly.

This can lead to biological effects, including abnormal cell development, some of which may not be seen for some time after irradiation.