Biological Effects of Radiation

Biological organisms are affected by exposure to radioactivity either through direct ionization of a biological "macromolecule", or indirectly through the ionization of water. Ionized macromolecules almost never function properly, due to the fact that their function is largely controlled by their shape and therefore by their charge distribution. Ionization of water produces "free radicals" (in this case neutral Hydrogen atoms and Hydroxide molecules) which are very reactive, leading very quickly to the breakage of bonds in a biological molecule. Then, again, the macromolecule is rendered ineffective.

In terms of structural effects, disruption of the chromosomes is most lethal, so sensitivity to radiation is greatest in cells which divide rapidly (gonads, bone marrow, intestinal epithelium and skin). Low velocity particles (alpha) are more destructive since they tend to interact more often than high velocity particles (beta). A mitigating effect occurs when the radioactive atoms are metabolized in some sense within the body. The radioactive decay mode provides a "physical" half-life, and the metabolic process provides a "biological" half-life. The two act as parallel paths for elimination of the radioactivity, and in analogy with parallel resistors in Chapter 4, the effective half life is then

1 / τ effective = 1 / τ physical + 1 / τ biological.


The next section is about elementary particles.

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©1996, Kenneth R. Koehler. All Rights Reserved. This document may be freely reproduced provided that this copyright notice is included.

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