rate variability was necessary. Portable Survey Instrumentation. The following instrumentation was utilized and is discussed below: 1. Alpha Radiation Detectors. Alpha detection is a problem on Eniwetok Atoll. The moisture associated with the tropical rainfall not only masks alpha emitters in soil, but also causes electrical problems with all portable survey instrumentation. 'The soil moisture problem was so great that until the very short "dry" season of January (when the average rainfall was only 1.02 inches per month and it had not rained for three weeks) alpha contamination was only detected by portable instruments on grossly contaminated surfaces. a. PAC-1S. Early in the survey, and during previous surveys, the principal alpha radiation detection instrument was the PAC-1S. Aircraft restrictions prohibited carrying of gas for the PAC-4G, a more sensitive and desirable instrument, and left only the PAC-1S5 as an alternate. This instrument detects alpha radiation using an alpha scintillation detector with an active area of 59 om@ and an aluminized mylar window thickness of 1.5 me/em°. The scintillation crystal is ZnS(Ag), silver activated zinc sulfide. The detector was connected to a survey meter which had } linear ranges, 0-2K, 20K, 200K and 2,000K counts per minute, full scale at 217 geometry. The complete assembly was weather resistant, but the probe was easily damaged by any sharp object, even a blade of grass. When thus damaged, it then became very sensitive to light, direct or reflected, and was rendered useless. — bd. LLL "Blue Alpha Meter." As the soils/radiation field effort pro- gressed, an LLL modification of a well known air chamber type alpha survey © Although not e™ instrument became available to the Eniwetok survey teams.