CHAPTER 4 SAMPLE ANALYSES AND DATA REDUCTION 4.1 SAPLE ANALYSIS Basic analysis consistec of gamma ccunting those samples collected for the determination of fallout contours end measuring the fallcut par- ticle size distribution and the annarent density of the varticles. 4.1.1 Counting Technique Two instruments were emnloyed in counting semnles. The 47 zamma ionization chamber was used where conversion of measured activities to gamma field intensities was desired. The gamme scinti]letion counter was used where relative levels of activity were desired, The 47 gamma fonization chamber and its calitration ere identical to that deserited in AECD-2367, This instrument consists of a pressurize? ion chamher, vibrating reed electrometer, and a Brown millivolt recorder. The chamter is fillec with argon et a pressure of 600 psig and onerates at a collection potential of 600 v. For low beckground the assembly is lead-shielded. Samnles are lowered into the center of the chamter. Be-~- cease the position of the source material is not critical, activities of _ large volumes of either licuid or solic samples cer, be measured. The gamma ionization chanter readinps were converted arbitrarily from millivolts to mr/hr in order thet all readires taken on fallcut he excressed on a conventional basis. A relationship between the chamber readings in my and a calibrated AN/PDR-T1B Survey meter was determined. Corres- ponding readings of ‘5 randomly chosen samples from Shot 1 were teken by both instruments. The eoustion of the resulting linear nlot showed mr/hr = . —tV_ , 519 With this relationship determined from “amples of hich levels of activity conversion of samnles of low activity, accurately measured in the 41 tonchanber, readings coule then be reliably converted to equivalent mrshr. The scirtilletion counter’ Vconsi sts of a detector assembly and Li,