vee ee ee el ee i Se ° Gasmta RADIATION Exposures FROM FaLLout Vol. 66 Neither the exact time of winds and rains nor the precise extent of dose-rate reduction can be predicted. These two param- ct crs are °bvious! . y uanta que . events to which a straight line function may be as: Sor only by the process of gencraliza cribed tion, as in Graph 2. The following esti. cantle mates nay be proposed:: For the first week followingfallout, the measured gamma ac- . ua . 4 a ee ar 1009 = Taste I: EstimaTeD ATTENUATION FACTORS OP Gamma Doss RATES FROM FALLOUT Approximate Structure Frame House ; First Goon cen veseeees beeveee Basement oaseeee (aide) tt! Basement (center)........ Muttistory Reinforced Conercte Loweriloors (away from windows). Dosenent eons? Shelter (cquivalent of 3 fect of earth) 4 *. CC Factor 2 10 +10 19 ~1,090 ~1,000 | ~ Gamma dose rate readings at i three feet above the ground 8 587 \ ” an island of Rongelap 4 iu a ® 100 | li — 2 = > , —_— is “es F e 3 SL ww ww Zuw 8 1b C ef: = pa o s fF -q ‘ a iy a on 10 on on 100 rey teri 1000 DAYS AFTER OETONATION Graph 2. Gamma dose ratcs on the island of Rongelap following detonation of March 1, 1954. tivity is assumed to decay according to (t)~'?, for the second week (t)~!:*, and for the third week and thereafter. (t)7'“ Justification for such values lies not in the high probability that they will occur at these times but rather in the necessity of generalizing (probably conservatively) in advance, so that some estimate of the parameter of weathering may be incorporated into evaluations of possible future contamination. Field measurcments, as well as calcula- tions, have indicated the attenuation of gamma dose rates to be expected from the shielding afforded by various structures. Obviously, there will be wide differences in this respect, depending upon the type andsize of the structures; Table I gives some rough estimates of this factor of shielding. For the moment, let us con- sider a situation in which no special evasive measures arc taken and people continue to live normally in the contaminated environ- ment. Great variation in the amount of