RADIATION EXPOSURE IN SUPERSONIC TRANSPORTS

SUMMARY ON UPPER LIMITS OF TOTAL RADIATION EXPOSUREAND CONCLUDING REMARKSBefore summing up the upper limits of total exposure, the previouslydiscussed facts on space and time distribution of cosmic radiations maybe recalled first. Both the galactic cosmic rays with their second-aries and the solar cosmic rays are limited in their main flux to geomag-netic latitudes above 50°, that is, to the northern and southern regionsbeyond these latitudes toward the poles. The ionization produced bygalactic cosmic rays in the high atmosphere decreases sharply toward lowerlatitudes or the equatorial region by a factor 1/15 or 1/30. Ionizationdue to solar cosmic rays decreases even in a larger degree below thislatitude. It may be recalled, furthermore, that during the 1 to 2 yearsof minimum sunspot activity the ionization produced by galactic cosmicrays within the atmosphere is higher than during the 9 years of highersolar activity and that during solar minimum years no major flare eventsare observed.Table III summarizes the upper limits of radiation exposure of thecrew on polar routes produced by galactic cosmic rays and solar cosmicrays if no precautions are taken. The effect of heavy primaries, andespecially of the terminal part of their tracks, is understated by usingthe comparison with the indicated number of s-particles and are moreadequately taken into account by multiplying the radium equivalent by anestimated factor lO. Their effects are not definitely known at thepresent time. However, consideration of the small number of hits percubic centimeter of tissue per day and of the short flight durationexperienced by the flight personnel and especially the passengers sug-gests that this effect may be insignificant.From table III, at unrestricted flights of the same crew on polarroutes for 40 b_r/month duty time at an altitude of 23 km3 the followingconservative upper limits (within the mentioned limitations) of totalexposure levels are obtained:During solar activity years,_200 percent of the maximum permissible level for continuous exposureDuring solar minimum years,_42 percent of this maximum permissible level