PLUTONIOM CONTAMINATION FOUND OFF-SITE FOLLOWING ONE-POINT DETONATIONS By M. W. Canter and 0. R. Pracax U.S. Public Health Service, Las Vegas, Nevada A series of four during the winter dental detonation potential spread experiments were conducted of 1955 to determine if accicould occur and, if so, the of contamination resulting from accidental detonation of devices. The off-site area includes all Lerritory within an approximate 100-mile radius, but. excluding the actual detonation area. A comprehensive report of these activities has been prepared and is available in the files of the Las Vegas Branch, Test. Division, Albuquerque Operations Office, U. 8. Atomic Energy Commission. Estimation of alpha contamination over many square miles of desert is not an established routine undertaking. The following methods were used for monitoring purposes: work-party conditions in areas where ground contamination existed. Pee Wee survey instruments are very useful in the field for locating contamination and for determining the order of magnitude of such contamination, Survey instrument readings should be considered as indicative of the mini- mum amountof alpha contamination present | ata particular spot andnot as areprcseatative value for an extended area of desert. Results of alpha survey instrument. monitoring indicate the extreme variability to be expected over a relatively small area on the same type of surface, For example, on a limited area of concrete pad, Pee Wee readings varied from 500 counts per minute to 1,400 counts per minute. portional alpha survey instruments (Pee Wee). (2) Fallout trays (80 square-inch sampling There appears to be no strict correlation between Pee Wee ground surface readings and laboratory counts on fallout trays located at the same spot. In order to have strict correla- adhesive alkyd resin. distribution over the entire trayarea in addition (1) Surface monitoring with portable pro- area) smeared with a relatively nondrying These were placed in rings around the detonation area to distances of approximately 30 miles. (3) Staplex air samplers using gless fibre filter papers andan effective filtering area of 63 square inches. Filter runs of 24 or 48 hours were accomplished without appreciable loss of flow rate. Air samplers were located in 11 populated communities surrounding the Nevada Test Site and at 12 locations on the site The maximum distance of air sampler location was 95 miles. (4) A mobile air sampler consisting of a Staplex sampler shock mounted on a trailer unit towed by a Jeep was used to simulate tion it would be necessary to have uniform to the same amountof dust overlay acting to shield each uniformly distributed particle. Fallout trays proved to be a simple convenient means of monitoring plutonium con- tamination. They are easy to monitor in the field and are easy to collect and transport to a central laboratory for more detailed analysis. Theyalso serve to differentiate new fallout from residual alpha “contamination which may be present in the same general area. Maximum contamination found on a fallout tray was 100,000 disintegrations per minute per square foot at a distance of approximately 5 miles. 185