-6procedure similar to that described by Lowman etal. The counts per minute (1957). (c/m) for each radioisotope were con- verted to disintegrations per minute (d/m) by applying the correction factors listed in Table 1. The size of the sample affects the geometry,and the correction factors listed do not include error due to the differences in geometry between the biological samples and the radioisotope standards used to calibrate the efficiency of the counting system. This error ranged from 10 per cent for the smallest biological samples to 60 per cent for the largest samples. The appropriate decay-correction factor was applied also to correct the values to the date of collection, Table 1. Correction factors used to convert gamma counts to disintegrations Radioisotope «40 factor 409 ¢s137 zn®5 Zn?>=Nb9> Co?? 16.5 54 14.5 8.6 cel44_p-144 106 p20 1 u Correction -Rh 40 ggg omariment otEnt 66.4 Historian § ARCHIVES