beluw the water surface in the attitude depicted in Figure 1.2. of The drop was made after passa cwater Shock waves by means of a preset time delay. ..gh-Range GITR. ASEL Gustave I recorders (ASEL-GITR) were borrowed by the project ior use as high-range detectors. The units originally designed and built by ASEL were repackaged by NRDL (Figure 2.4). Because the basic device is described in existing literature (References 49 and 50), only a brief description is included here. The instrument is capable of recording dose rates as high as 10° r,/ hr with a time resolution of 0.1 msec. The gamma intensity record is made on 450 feet of 1-inch magnetic tape, which travels at 60 in/sec, providing a 90-second record. The basic circuit was modified by the elimination of the cathode follower originally used between the detector and the amplifier unit. The repackaged instrument is 19 by 16', by 16 inches high and weighs approximately 110 pounds with power supply. The ASEL detectors were calibrated on a special range set up on Parry Island with a 200- curie Co® source. ASEL-GITR’s were installed only on coracles less than 6,500 feet from surface zero, the recording element being placed in the instrument well with the detecting ele- ments installed on the deck (Figure 1.2). The ASEL-GITR received a warmup Signal at minus 5 minutes, and a minus-5-second signal to start the rapid tape transport. received from the trigger-control box. Both signals were 2.2.4 Incremental Fallout Collector. The incremental collector (IC) has been used on many field operations and has been frequently described (References 33 and 58 through 60). The current instrument was redesigned to reduce the unit cost and to bring the collecting surface as near the top of the instrument as possible (Figure 2.5 and Insert A of same figure). The instru- ment is 6 by 29 by 32 inches high and weighs 95 pounds with a complete set of trays. In essence, the IC obtains a series of 58 fallout collections over uniform time intervals regulated by the trigger-control box. Fifty-eight specially prepared trays are placed upon a spring-compensated elevator platform so that the stack of trays is directly below a sampling port approximately 3 inches in diameter, the top tray being exposed. The trays are then individually indexed onto a receiving platform by an electrically actuated pneumatic system. The exposure interval planned for Hardtack was 1 minute, and the instrument was timed and actuated by the trigger-control box. IC’s were installed flush with the coracle deck (Figure 1.3) or flush with the general level of the platform instruments on DD-592 (Figure 1.16). To reduce shadow bias (Appendix F and Reference 61), the collecting surface was brought to within Y, inch of the top of the instrument. Lucite trays 4 inches square and containing a circular well, 3% inches in diameter and 4 inch deep, were used (Figure 2.5, Insert B). The well contains several thicknesses of filter paper capped with a perforated 20-mil polyethylene disk. The polyethylene disk is inserted by rotating it through a key slot ina Y,-inch lip projecting inward from the top of the well; thus, the disk with the filter papers beneath it is held firmly within the tray well. The perforated disk was coated with a thin layer of a grease Specially developed for use at the EPG (Reference 33). This grease is made by adding polyethylene to Lubriseai (about 3 percent by weight) to raise its melting point to 190° F. The grease was in- tended to trap solid particulate matter, while the filter paper beneath the perforations retained the liquid fraction. The trays were designed so that the IC could be loaded or unloaded ina Single operation, which alleviated recovery problems in high-radiation fields. 2.2.5 Film Packs. A large number of film packs were used by the project on the coracles, aboard the target ships, and as FFP’s, which were either free-floating or anchored. Regardless of the manner in which these film packs were placed in the array, the basic element consisted of two packets of (iim placed inside an NBS holder (Reference 62). This holder was Seated inside a plastic cigarette case, which in turn was placed into two independently sealed plastic bags; thts procedure both reduced humidity and oxygen damage to the films and afforded a rapid means of decontaminating film packs upon recovery. The whole package was then wrapped in aluminum foil to reduce absorbed heat, since the film used deteriorated under elevated temperatures. . in 57