236 LOWDER, BECK, AND CONDON a A, COLORADO SPRINGS, COLO., OCT. 11, 1962 B, ARGONNE, ILL., OCT. 15, 1962 _ 0.75 MEV 957 — Nb 104 F— 4 3 1er aan Ww 2 O W 2.62 MEV 2087| 12 ifL _ Let 20 | tt tN 60 100 140 180 220 260 CHANNEL NUMBER Fig. 2—Tuo typical field spectra obtained during late 1962. The cosmic, natural-gamma, and fallout-gamma levels are all somewhat higher at location A. absorption peaks, at 0.5 Mev (!4°Ba—‘!°La, !Ru, and Rh), 0.75 Mev (5Zr—*Nb), 1.46 Mev (!°K), and 2.62 Mev (79871), as well as other minor peaks, including the 1.76 Mev *!*Bi peak. By a determination of the area under these peaks or of the total number of counts in energy bands bracketing them, estimates can be made of the contribution from each emitter or series of emitters to the total dose rate in air at 1m aboveground. In the former method the area under each total-absorption peak is approximated by asSuming a linear continuum under the peak on semilog paper, fit to the values on each side. This area, although not necesSarily identical to the true number of total-absorption counts, is as- sumed to be directly proportional to the incoming flux of primary photons. This has been satisfactorily checked in the laboratory for several energies and over a wide range of flux values. If a uniform source distribution in the soil for the naturally occurring radioisotopes and an exponential distribution for fallout emitters are assumed, the flux and