Radiation Hazards and Manned Space Flight.

T HE POTENTIAL medical hazards of man's venture into space will span a number of disciplines in regard to the pathology and deranged physiology to which the human body may be subject in travel beyond the earth's atmosphere. Not the least hazard is that having to do with the effects of radiation to be encountered in free space. This problem is one which is receiving considerable attention from astrophysicists, radiobiologists, and others interested in the effects of ionizing radiation on tissue. The radiation in question can be divided broadly into three (3) categories. The first is cosmic radiation which apparently originates in interstellar space, and is therefore present in this galaxy and in others. The cosmic radiation has two (2) components both of which are particulate radiation. The largest component consists of protons (nucleus of hydrogen atom) comprising about 79 per cent of the radiation and alpha particles (helium nucleus) amounting to about 20 per cent of the total. The nuclei of heavy elements such as carbon, oxygen, nitrogen etc. up to at least iron comprise the remaining 1 per cent. 4 The cosmic ray particles are among the most energetic known. Energies range from a few million up to several billion electron volts. 5 As these particles enter the earth's atmosphere they interact with the atoms of air causing ionization with the production of a number of secondaries, (deflected particles and 'electrons) and eventually dissipate their energy so that the dosage at sea level from this radiation amounts to less than 100 milliroentgens per year. The second source of radiation encountered is that designated as the trapped corpuscular radiation. This consists of two wide belts of particulate radiation surrounding the earth except in the polar regions. These are called the Van Allen belts after Van Allen who discovered them in 1958. The lower edge of the inner Van Allen belt varies from an altitude of about 450 kilometers above the earth's surface over Chile to an altitude of about 1400 kilometers over Australia. It extends outward into space to reach a maximum inten-