ABSTRACT
The ionisations produced by the secondary electrons result in the production of the very reactive chemicals with unpaired electrons described in Chapter 3. The reactive chemicals are called radicals. Water makes up 60% of the tissues of the body and, along with other molecules, some water molecules will be ionised by exposure to X-rays or ?-rays. Because they freely mingle with the non-ionised molecules, radicals produced by the ionisation of water are called free radicals. However, the term free radical is applicable to any radical that is free to diffuse (move around in a fluid medium). The chemical radicals produced by radiation indiscriminately attack proteins, DNA and other important large molecules, known as macromolecules. Radicals, however, have a very transient existence, only lasting about a thousandth of a second, and can be ‘mopped up’ by sulphur-containing compounds within the cell. They can therefore be envisaged as tiny short-lived ‘chemical bullets’ which have very local effects just on small portions of the large cellular macromolecules.
