"Air" Dose, Tissue Dose, and Depth Dose of the Cosmic-Ray Beam in the Atmosphere

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Abstract
In assessing possible biological effects of cosmic radiation, two phenomena are distinguished: (1) the total ionization; and (2) absorp- tion events of high local energy concentration in the microstructure of exposed tissue. The air dose from total ionization starts with 0.1 millirad/24 hours at sea level and reaches a maximum of 15 millirad/ 24 hours at 75,000 feet altitude. Limiting values can be derived for the ratios of air dose to tissue dose and of entrance to exit dose for exposures at various altitudes. Both ratios exhibit some unusual features as compared to ordinary penetrating radiations. The spatial distribution of maximum ionization hits in a compact target shows a highly structural pattern with a focal zone of maximum intensity. The biological significance of these events is little understood. Cellular destruction has been demonstrated for various specimens including mammalian tissue in vivo. Yet no clues as to the general reaction which such local damage might produce in the organism are available. The low energy part of the primary cosmic ray spectrum, which is the main contributor of hits of maximum ionization, is also subject to marked intensity fluctuations correlated with the solar cycle.
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