Estimates of radiation doses in space on the basis of current data.
A gross survey of data on Van Allen belt radiations, galactic cosmic radiation, and solar cosmic radiation is presented. On the basis of these data that are, in part, fragmentary and uncertain, upper and lower limits of rad doses under different amounts of mass shielding are estimated. The estimates are preliminary especially in the cases of chance encounter with solar flare protons. Generally, the relative biological effectiveness of the high energetic space radiations and their secondaries appear insufficiently known to give detailed biological or rem doses. The overall ionization dosage of the low level galactic cosmic radiation in free space is estimated to be even in solar minimum years equivalent to less than 50 rem/year or 1 rem/week. Mass shielding up to 80 g/cm2 would not reduce the ionization dosage but would shield against heavy primaries and heavy ionizing secondaries, thus reducing the biological dose. The flux of energetic protons in the maximum intensity zone of the inner Van Allen belt is by about four orders of magnitude higher, their energy and penetration power, of course, lower. A shield of 25 g/cm2 would reduce the dose rate from 20 rad/hour under 2 g/cm2 to 5 rad/hour. These proton dose rates and also the electron and X-radiation dose rates under some g/cm2 shielding of low z-number material will not constitute a radiation hazard for flights straight through the inner and outer belt in about two hours. Staying within the maximum of the inner belt for two days would, however, lead even within 25 g/cm2 depth of outer shield and body itself to a dose of 200 rad which is on the permissible limit. Extreme solar cosmic ray events or proton showers of high intensity and a duration of days occurred with a frequency of 1-4 per year during the last highly active cycle. For the penetrating, most intense high energy event of February 23, 1956, the dose within 25 g/cm2 is estimated to have been in the order of 50 rad. In most cases the dose decreased more rapidly with penetration depth and would have been even in multiple events with such high shielding below critical levels, especially on inner organs. On the surface of the body and in a lightly shielded space vehicle or protected by a space suit only the dose can, especially in multiple events, reach values of 1000 rad and more.
Foelsche
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NASA Langley Research Center, Hampton, Virginia, USA.
D001272:Atmosphere; D003359:Cosmic Radiation; D018534:Earth, Planet; D004583:Electrons; D005118:Extraterrestrial Environment; D008962:Models, Theoretical; D009502:Neutrons; D011522:Protons; D011829:Radiation Dosage; D011835:Radiation Protection; D019445:Solar Activity; D013026:Space Flight / Q000295:instrumentation; D018531:Spacecraft / Q000295:instrumentation; D014965:X-Rays
D011522:Protons