de The relative peak height description permitted a general comparison of samples from different shots, from different locations for a given shot, and for the same sample at various times after burst, It should be emphasized that the descriptive technique used here, namely, analysis by relative peak height, is only a qualitative summary of the important photon energies present and has no relation whatever to the true photon-energy distribution of the radiation source, 5.14 Absorption enents Aluminum absorption measurements were made with absorbers ranging in thickness from 0 to 3430 mg/sq cm. Before plotting, the aluminun absorber thickness was corrected for air and window thickness. Lead absorption measurements were taken with lead sandwiched between two aluminum absorbers. The aluminum absorber next to the counter window had a thickness of 1590 mg/sq cm and that just above the counting source 861 mg/sq cm. The lead absorbers ranged in thickness from 0 to 29,0 g/sq em, The absorption measurements were taken at various times after detonation on one fallout sample from each of Shots 1 through 4. 5Selehel Lead Absorption A summary of gamma ray energies from the lead absorption curves is given in Table 5.1C. These curves were analyzed into three components which give the "apparent" gamma energies although it is known that there are many different gammis contributing. The soft, medium, and hard components were then used to compare different samples with each other. The amount of each component was corrected by the counter efficiency for the apparent energy. The usual procedure of analyzing absorption curves was used; tne "zero absorber" count rate was determined by extrapolating the three lines on a semilog plot to zero absorber thickness. The energy of each line was determined from Pb half-thickness curves; this energy was used to determine, from Fig. 2.1, the component crystal efficiency which was, in turn, used to weight the "zero absorber" count rate for each component to determine the relative amount of that component, From these data the following conclusions may be drawn: (1) Between 0.3 and 26 daye there appeared to be no appreci- able change in the energy of the soft gamma component, The average energy for all soft gammas observed was 0.16 Mev with a maximum deviation of 0.04 Mev. (2) Between 0.3 and 26 days there appeared to be no signifi- cant change in the energy of the medium gamma component. The average energy for all medium gammas observed was 0.37 Mev with a maximum deviation of 0.11 Mev. (3) There were larger variations in the energies of the nard gammas with respect to time especially for Shots 2 and 3. However, no definite trend is apparent as may be seen from Table 5.11 where the hard gamma component has been averaged for each shot, The over-all hard gamma energy average was 1,3 Mev with a maximum deviation of 0.5 Mev. (4) There appears to be no trend common to all shots for the 117