CHAPTER 2 DIROUTTAY In the spring of 195k, Operation Castle, s series of atomic tests, wes conducted at the Atomic Energy Commission's Pacific Proving Grounds in the Mershell Islands. Again, as in other recent test series (1, 2, 3), an extensive network of gummed cellulose scetate file 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 inoluie a 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 Navy and Coast Guard, and two by the Atomic Bomb Casualty Commission. The Canadian Meteorological Services cooperated by operating nine stations and the Canadian Atomic Energy Commission one. All stations were scheduled to make two simultaneous 22-hour collections starting at 1230 G.C.T. each day. The mechanism of transvort of stomic debris and the representetiveness of gummed fils samies hsve 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 climstes consisted of 8 0.5 ft* plate warmed by a thermostatically-controlled electric heating element. The melt water was allowed to run off the surface, making the observations comarable to those of rainfall on 8 conventional gummed film stand. To simplify the procedures used in correcting for decay and assigning masured activity to particulsr bursts, a somewimt arbitrary system of burst assignment was. used in those cases where the burst responsible for the radioactive debris was uncertain, All radio- activity collected from Pacific Islands and from ships was assumed to have come from the latest burst, activity elsewhere in the world, from the burst prior to the latest. Where there were definite ~jl« r vty In addition, single gummed film stands wre installed on mst ships of the Military Sea Transport Service scheduled to be on routes in tae Pacific Ocean. The ship collections were also made daily.