gas flow counting chamber. Hence the correction factor was approximately 2.0. Backscatter. Backscatter was previously determined for p32 in our Nucleometers as being 30 percent (see p. 24 of AECD-3446). The same correction factor, 35 = 0.77, was used again this year. Coincidence. The loss of counts due to coincidence was determined empirically. Small amounts of p32 were dried on tinfoil and the pieces of the P32 tinfoil, for which the counting rates had been determined, were placed one at 4 time side by side on the counting plate. After each piece of the p32 tinfoil had been placed on the plate a count was made. The expected count, which was the sum of the individual counts, was divided by the observed count to determine the correction factor. For observed counts less than 80,000 e/m, no correction was made for coincidence; for counts of 80,000 to 160,000 per minute, the correction factor was 1.01; for counts of 382,000 to 392,000 per minute, the correction factor was 1.07. Correction factors were also determined for intermediate values. For small corrections the counting rate as determined theoretically from the formula N * tout held true (N = true counting rate, n = observed counting rate, and t = recovery time of register = 5 microseconds). Background. The background values were determined by interpolating between background counts at the point (i.e., time) when the sample count was made. Usually about five - 12 - 20