The biological effects of heavy cosmic ray particles.

There has been rather extensive biological experience with most of the radiations known to exist in space beyond the earth's atmosphere, with the exception of the very high energy heavy particles which form a small part of the galactic cosmic rays. These particles cannot be reproduced in the laboratory, but from experiments with smaller particles, and from theoretical considerations, there was reason to fear they might be very damaging biologically. A very narrow beam of 22 MeV deuterons has been developed which will have the same biological effect as the track of a very heavily ionizing particle. Using this microbeam the following results have been obtained on mice: (1) brain tissue is very insensitive to this type of radiation, (2) this radiation will cause minute abnormalities in the lens of the eye but in general these do not progress to form cataracts; but if they do, they remain extremely small, (3) if a hair follicle is hit, the hair from that follicle will turn grey. It is concluded that the heavy cosmic ray particles do not pose a serious problem for manned space flight.