ahh Bpal40_7,q140) to dose rate in a manner analogous to the peak method described previously for the natural emitters. case of fallout, however, In the the emitters are assumed to be dis- tributed in the soil according to the relation S = Soe 722, where z is the depth beneath the surface in cm., So is the emitter concentration at the surface in units of curies/cm>, and S is the concentration at depth z. We have chosen the constant, a, to be 1/3 cm-l since, on the basis of available depth distribution data, this choice appears to be a reasonable approximation for other than recently deposited fallout. The cal- ibration coefficients for the fallout peaks (see Table I) are quite sensitive to depth distribution (i.e., the value for "a"), and the dose rate from freshly deposited fallout, whose distri- bution would be better described by a nearly plane source, will be overestimated by our model. The conversion factor used for the 0.5 MeV peak is based on calculations for Rh106 | since this isotope dominates the 0.5 MeV activity for thermonuclear weapon fallout more than about six months old. The second estimate of fallout dose rate is obtained by subtracting the sum of the natural gamma dose rate estimates from the "best value" of the total measured terrestrial gamma dose rate. The two fallout estimates agree fairly well in general, suggesting that Zr25-Nb?5 and Rh196 were the primary fallout gamma contributors during these surveys. Any signifi- cant Csl37 (0.66 MeV) contribution would be partially included with that of Zr95-Nb95 since their total absorption peaks generally overlap in our spectra. Other fallout emitters generally constitute only a very small proportion of the dose rate. VALIDITY OF DOSE RATE VALUES The best indication of the validity of the dose rate values presented in this report is the excellent agreement between the sum Of the individual components and the total terrestrial dose rates, obtained over a wide range of terrestrial gamma fields. Furthermore, independent soil concentration determinations of K49 and Th232 at many Of our survey locations have shown good agreement with concentrations inferred from our dose rate estimates. Unfortunately, U238 soil concentrations derived by assuming radioactive equilibrium in the decay series are not directly comparable to our U238 dose rate values due to the