scaler unit Radiac Computer Indicator CP-79/UD (NavShips 91892). The detector assembly mcunted inside a commercial lead castle consists of a@ cylindrical sodium iodide crystal 1.5 in. in diameter and 0.5 in. thick, an ROA 5819 photomultiplier tube, and a pre-anvlifier unit. crystel is shielded from the sample chamber by 0.25 in. of aluminun. The The counters used were completely evalusted for coincicence loss by using six paired sources and employing a least square evalvation.9/ Coincidence loss varied from 1 per cent at 100,000 c/m to 10 per cent: at 2,000,000 c/n. All differential fallout collections were counted under fixed geometry and corrected for background and counter coincicence losses. No attempt was made to obtain any more than relative counts between sammles. 41.1.1 Total Collectors Many of the total collectors contained considerable quantities of rain water which fell during the relatively long period between placement and recovery of the instruments but not during the period of fallout. In these cases there was leaching of the fallout activity into the liquid. Preliminery separations of the liquids and solids were achieved by decantine the gross samples. Final separations were then obtained by centrifuging which left the resultir.z liquid clear or, in some cases, containing colloids. The liquid volumes were measured and the solids dried and weiched. The samples were placed in 100-ml lusteroid centrifuge tubes and gamma activity measurements were made on these samples with a é7 gamma ionization chamber. In instances where the liquid fraction ex- ceeded 100 ml, these samples were concentrated to the desired volume after acidification. 4Zelele2 Cummed Paper Collectors The acetate-backed 1-ft squares of gummed vaper were removed from their cardboard mounts and folded to fit into 100-ml lusteroid tubes. Their gamma activities were measured with a 47 gamra ionization chamber. 4.1.1.3 Vifferentiel Fallout Collectors Each of the 40 colyethylene collecting jars was removed from the collector and decontaminated on the outside. The jar openings were then canped with cellovhane 0.001 in. thick held in positisn with a rubber band, CGarma counts were then made rith : scintillation counter. 4.1.2 Particle Size Measurements The particles were fixed with Krylon cn a framed cellophane membrane. Contact autoradiographs were made using Eastman Commercial Ortho film. The outer island analysis emvloyed nuclear emulsion stripping film with the particles fixed to the non-enmulsion side of the film £5