Although a knowledge of the depth distribution may be critical yee oy is ay. if the” when using in situ measurement techniques to determine concentration values, this is not the case if these techniques are used to determine external exposure for rate values. The exposure rate conversion factors (last column, Table 1) are relatively insensitive to rather large variations or uncertainties in the depth distribution. Comparisons made be- tween exposure rate values determined using in situ techniques with those obtained with a pressurized ionization chamber are in general quite good (see, for example, Beels, et al. (4) Table 21). The conversion factor used for 13’cs was 3.6 R/h per cps. Concentration values may be obtained from the exposure rate values by multiplying the appropriate ratio of the conversion factors given in Table 1. For 60¢5, a conversion factor of 20.5 used with the 1173 keV peak or 22.3 peak. In principle, R/h per cps with the 1333 keV either of these peaks could be used to determine the total exposure rate resulting from same result. R/h per cps can be In practice, however, different in the two results. 0c; both should lead to the some measurements were slightly In these cases the average valuc was used. The minimum detectable activity (MDA) for the in situ results was set at the 30 level where sigma equals the square root of the sum of the net photopeak counts plus twice the background counts. Because the MDA is a function of the background under a given photopeak, which varies from location to location, there is no unique number for the MDA for any given isotope. The actual value for a specific isotope varies slightly from location to location, and the values of 0.5 pCi/g for 241 an, 0.2 R/h for 137¢5, and 0.5 R/h for 60co used in the present report represent the worst-case situation as actually encountered at Enewetak. ~ GU 01 1638 9 - .