CHAPTER GAMMA ENERGY-DOSE SPECTRUM b.] FHOTON FLUX SPECTHIM The fallout material deposited on the ground produced a large area plane source of radiation, Before a total gamma dose could be calcu} lated, it was “necessary to correct the dose rate readings in air taken z with the survey instruments with the meter resporse factors found to bef ‘necessary for different energy regions, Further, to estimate the dis~, tribution of dose with depth in tissue required a knowledre of energy’ distribution of the incaning flux in a given exposure geometry, For a source as large as these fallout fields, this enerzy distri<’ tetion will be a functicn both of the original source energy and the enerry derradation effect of eos threy ea widens air, interven vere A ” moh. 14O of evaluating the latter, which was due mainly to Compton scatteting in air for the fission product eneryy region, has been presented in — Reference 7. This technique was enployed here, Energy spectra of the . CASTIE fallout itself has been measured with a scintillation spectrome~ ter on a series of cloud samples as early as H+ 4 days, ‘The data have been published in Reference 8. The preliminary data on the earliest of these, a 94-hourscld cloud sample, were used in the calculations suneed in Reference 16, These are given in Table ).1 (Reference 9), This 9k-hour sample from Shot 1 represents the closest approach to the actual time during which the exposures occurred, After the conclusion of the test series, analysis of early data from other shots continued and later spectra for all shots were ana- lyzed. None.of the other spectra are for times _as early as H + 9 hours, For the later detonations the proportion of Np*39 (average parma -ener-=3 5, = 23 kev, WO percents E2 = 105 kev, 11 percent; By = 50 kev, ts percent) in the fallcut samples was found to be much higher than that given in Table 4.1, An extreme case, for example, is the data for 2 Shot h on 26 April at H+ 5.3 days which is given in Tatle b.?. Here See “e:": of thethe low tota energy portion than 100 kev was measured as 60 percent l phot on fluxof , less Two later determinations on. anot her Shot 1 o sample (1-L, Tatle 3 of Keference 3) show these low energy proportions as 55 percent at H+ 4.1 days and Sh percent at H + 5.2 days as well (Tatles h.j and 4,4), Later data thus tended to show thatthe initial estimate of low ener,y rediation was low, Hence, revised estinates of the total doses will be presented here on the basis of the additional data for which the counting statistics were tetter than on the Shot 1, H+ 9 hour sample, These Spectra, it must be emphasized, are for