CHAPTER 1 In the spring of 1954, Operation Castle, a saries of atomic tests, was conducted at the Atomic Energy Commission's Pacific Proving Grounds in the Marshall Islands. Again, as in other recent test series (1, 2, 3), an extensive network of gummed cellulose scetate film sampling stations wes established by the New York Operations Office Health and Safety Laboratory to monitor the deposition of radioactive dust resulting from the detonations. For the Castle tests, the gummed film network was expanded considerably to incluie 8 representative world-wide network of 122 stations (Figures 1.1 and 1.2). The U. S. Weather Bureau operated 39 stations in the continental United States and 1); at overseas locations; the Air Weather Service operated 23 overseas stations, the State Depart- ment 31, three were operated by the Mavy and Cosst Guard, and two by the Atomic Bomb Casualty Commission. The Canadian Meteorological — Service cooperated by operating nine stations and the Canadian Atomic Energy Commission one. All stations were acheduled to make two simultaneous 2)j-hour collections starting at 1230 G.C.T. each day. In addition, single gumed film stands wre installed on mst ships of the Military Sea Transport Service scheduled to be on routes in the Pacific Ocean. The ship collections were also made daily. The mechanism of transvort of atomic debris ani the representa- tiveness of gummed film samples have been discussed in previous reports. The only changes in technique involved in the present series of observations concern the decay correction and the installation of snow melting devices at certain northern stations. . The ed gummed film stand for use in snowy climates consisted of 8 0.5 ft* plate warmed by a thermostatically-controlled electric heating element. The malt water was sllowed to run off the surface, making the observations comparable to those of rainfall on a conventional gummed film stand. To simplify the procedures used in correcting for decay and assigning measured activity to particular bursts, a somewimt arbitrary system of burst assignment was used in those cases where ths burst responsible for the radioactive debris wes uncertain, All radio- activity collected from Pacific Islands and from ships wes assumed to have coms from the latest burst, activity elsewhere in the world, from the burst prior to the latest. Where there were definite a a ¥