only 6.4 percent and 11 percent of the total exposures were delivered hefore shuck arrival] at these two stations. 3.2 NEUTRON RADIATION The basic neutron-flux measurements were made with acuvation detectors whose indicated effective threshold energies were: Detectcr: Au, Au-Cd Threshold: <1 ev Ta, Ta-Cd <Lev § > Additional measurements were made with fission detectors and germanium crystals, primarily to test their usefulness. The fission detectors were used in two ways: counting fission fragments in a photographic emulsion and counting gammaactivity from fission products after recovery of the samples. The fission detectors used and their effective t’ reshold energies were: «Detector: U8 Threshold: 1.5 Mev , Np™? 0.64 Mev Th 1.5 Mev Pu 200-1,000 ev? The Shot 1 data from the activation and fission detectors are summarized in Figure 3.3; the fission detector data from Shot 2 are tNustrated in Figure 3.4. The germanium crystal (Ge) dose data agree in order of magnitude with the threshoid detector data. There was a large scatter in the Ge data, indicating that the detectors were not reliable in the form used. 3.3 FALLOUT DISTRIBUTION 3.3.1 Instrumentation. The following procedures were used to furnish information on the distribution of fallout activity after each of the Castle shots (some of the colleciors also provided samples for chemical, physical, and radiochemical studies of the fallout material): 1. Survey readings were taken by project personnel and the Rad~-Safe organization at island stations at various times after the shots. 2. Readings of total residual-gamma exposure at island stations were taken from film badge and chemical dosimeters. 3. The activity of samples from total fallout collectors was related to the infinite- field exposure rate by normalization at island stations. Total collectors of the funneland-bottle or gummed-paper type were placed at island stations, on rafts anchored in the lagoons, and on free-floating buoys placed north of Bikini Atoll during the last few © days before shot time. 4. Gamma-exposure-rate recorders were placed at some island stations to provide data on the time of arrival, rate of arrival, peak activity, and decay of fallout. 5. Incremental fallout collectora were used to collect samples during 5- to 30-minute intervals and to provide data on time and rate of arrival of fallout. 6. After Shots 5 and 6, surface and aerial surveys of the ooean fallout area were performed to measure the activity in the surface layer of the ocean and ita depth of penetration. The existence of a mixed layer in the ocean down to the thermocline, with little mixing below, enabled these measurements to be related to the total activity deposited. 1 Depending on amount of B® shielding around sample. 44