Cosmic radiation is composed of a relatively large number of light particles such as protons and electrons, and small numbers of heavy particles which are the stripped nuclei of elements as heavy as iron. The biological effects of the light particles are reasonably well known, but since the heavy particles penetrate only a short distance into the upper atmosphere and are too energetic to be reproduced in any accelerators now in existence, there has been almost no opportunity to study their biological effects. It can be shown theoretically that each individual heavy particle would create in tissue a tract having a densely ionizing core a few microns in diameter in which radiation doses may be as high as 10,000 rad.* The dose falls off rapidly at greater distances from the axis of the track, but it is still appreciable at a radius of 0.012 mm. This has been verified experimentally
von SALLMANN L, CURTIS HJ, GRIMES P. The Effect of a Deuteron Microbeam on the Mouse Crystalline Lens. Arch Ophthalmol. 1962;67(2):163–170. doi:10.1001/archopht.1962.00960020165010
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