Biological Effects of Ionizing Radiation

Abstract

Ionizing radiation affects human tissues by depositing energy as it passes through the body. During the tenth of a trillionth of a second after radiation hits an atom in a tissue, an electron is stripped from this atom. This process is called ionization. As the electron is negatively charged, the remainder of the atom, which was previously neutral, becomes positively charged. Both the electrons and the ionized atom are very unstable, and during the next tenth of a trillionth of a second, they undergo a complex chain of physicochemical reactions, creating new molecules, including particularly reactive ones known as “free radicals.” These, in turn, during the next millionth of a second may interact among them­selves or with other molecules and, through processes not yet fully understood, may produce chemical changes in some molecules that are biologically important for the cells, such as those carrying the essential information for their function. It is through these changes that biological effects occur over any time span, from a few seconds to many decades after irradiation. These changes may kill cells outright or alter them in ways that will lead in the course of time to cancer or to genetic effects.

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