Implications of space radiations in manned space flights.

T H A T ionizing radiations produce deleterious biological effects 'has ,been proven by sixty years of experience and experimentation. Qualitatively, the effects of all ionizing radiations, whether they are gamma rays or heavy primary cosmic parti.cles, are the same and are a manifestation of the ionization produced in cells and tissaes,. Quantita~tivety, the effects are dependent on quality and nature ,of the radiation, on the specific biologic effect under consideration, and in many cases .on the rate at whic,h the radiation dose is delivered. D,os.e rate dependence is illustrated by the lethal effects o,f Co 6~ gamma radiation on mi.ce. When delivered at :the rate of 30 r ,per minute, a,bout 700 r will result in death .of 50 ,per .cent of a large population of animals wi~;hin 30 days. V~hen delivered at a close rate of 100 r per ,day, the LD'~0 close is about 2000 r. (,)uamitative dependence of biologic effect on the .characteristics, of the radiation and the conditions of exposure make imperative the collection of more physical data on space radiati'ons before their implications to manned space flight can be adequately evaluated.