surrounded each methane-flow counting chamber used in con- junction with the Nucleometers to give a background of only about 45-50 counts per minute (c/m). The same counting equipment was used throughout the seven years covered by this report. Counting time followed the schedule of WT-616:20 during the earlier counting: C/m, sample Counting time, plus background minutes <~-500 500-1000 1000-2000 > -2000 20 10 5 2 For later counts, as more ett machine time became available, longer counts of from 30 minutes to several hours were frequently possible for the low-counting samples. The absolute level of radioactivity as indicated in the column of Table 1 headed "Plate count, 1000 days," serves as an index to the reliability of the points. Graphing and Reproduction Values from the decay data-sheets were plotted as circles on thin logarithmic graph paper. Even where circles overlapped, almost all of the values were graphed. the nearest curve, and lines Free, outstanding circles pertain to connect those points whose identity was