Biological effects of high energy radiations

The primary data for quantitative estimation of radiation effects in humans have been from epidemiological studies of human populations exposed mostly to high doses of sparsely ionising γ rays. For practical applications, this information has to be extrapolated down to the low doses and low dose rates normally encountered, and sometimes also to other types of ionising radiation such as alpha-particles on earth or high energy particles in the upper atmospheres. Experimental and theoretical studies provide essential guidance to these extrapolations. Nevertheless there remain appreciable uncertainties in the actual risks of cancers, of all or particular types, and of genetic effects that may result from exposure of humans to unusual radiations. (author)