CHAPTER 3 RESULTS 3-1 GENERAL Documentation of fallout included:(1) surveying of fallout samples and the areas from whence they came; (2) studying decays; (3) extrapolating the beta activity results to estimted activities at sampling time, and (4) studying the activity per unit weight or volum, energies, particle size, and particle characteristics of the radioactive fallout. 302 BETA COUNTING EQUIPMENT, TECHNIQUES,AND CORRECTION The glass counting cups were removed from the trays, externally decontaminated and counted by Tracerlab G-M tubes with window thicknesses of less than 2 mg/cm?. The tubes were mounted in vertical lead shields, Technical Associates Model AL14 A,having a wall thickness of 2-in. lead, 0.25~in. brass, and 0.25-in. aluminum. A geometry-defin- ing brass plate was inserted between the G-M tube and the sample.4/ The output of the tubes was fed into Atomic Scalers Model 1060 having a characteristic resolving time of 5 microsecondse The samples in glass cups were counted for beta activity in the following mannert samples with activities greater than 1000 cpm were counted for 10,000 counts, samples with activities less than 1000 cpm were counted for 10 min. Each sample was counted twice; in cases where _ the two counts did not agree within one standard deviation,a third count was taken and the three counts averaged.e It was necessary to apply several corrections in order to approximate the disintegration rate of the samples. The method mst commonly used to obtain the disintegration rate of a sample is to compare the sample under consideration with a known source counted in an identical manner. However, there is no one known source which represents mixed fission products. The procedure used here evaluates the various correction factors in terms of the sample itself and thus avoids the errors associated with a direct comparison with a singleisotope standard. The procedure is as follows: 1. The raw cpm were corrected for coincidence loss._5/ 34