mr, hr. This low reading could be explained by assuming that the coarser suspended mater:al (probably in the form of CaCO, sank, scavenging most of the radioactive debris as it did so. 3.4 GAMMA RADIATION FIELDS ABOARD TARGET SHIPS Gamma fields aboard all target ships were measured by 2 std-GITR detector Similar to that used onthe coracles. Although tape readout in some cases was accomplished bya different method, limits of accuracy and restrictions similar to those already described for coracle records apply to shipboard gamma records (Sections 3.3.1 and 3.4.1). Most recorder transports used aboard the skigos were the 60-hour type (Section 2.2.1) rather than the 12-hour type used in the coracles, and the detector was muunted ina different casing (Figure 2.3}. Since depos- ited radioactive material may be neglected, the difference in response due to detector mounting should be minimal; however, the lower tape transport speed and the fact that the shipboard installations had no timing blank (Section 2.2.7) combined to reduce time resolution to about +3 seconds. The 60-hour tape transport was used aboard all target ships with the exception of the pilot house and centerline-forward stations on the EC-2 for Shot Umbrella. The slowtransPort speed was selected, despite the risk of Saturation, so that in the event of large deposits of radioactive material, the decay rate would be recorded for a sufficient length of time to permit a complete radiological survey of the vessel before the GITR record terminated. In addition to the GITR’s, film packs were placed at approximately 20 locations aboard the target vessels (Section 1.3.3) to establish a relationship between GITR stations and other shipboard positions. The reported accuracy of these film packs is +20 percent (Section 2.2.5), but the correlation between film pack and solid angle plots versus frame number (Section 3.4.2) Suggests higher accuracy. After each shot, a precise radiological survey of all topside decks was made with calibrated Cutie Pies (Model CP-3DM beta-gamma survey meter, Reference 103) in an attempt to extend GITR and film pack data to still other shipboard locations. The final positions and attitudes of all target ships are tabulated in Table 3.26 (References 75 and 104); movement of the ships after each shot has been estimated from photographs and is also included tn the table. This movementof the ships should be remembered when considering these shipboard records. After Wahoo, the EC-2, DD-474, and DD-592 all changed positions shortly after zero time (Figure 2.1). After Umbrella, the DD-474 broke her stern mooring and swung on her forward anchor. The final position of the DD-474 was about 500 feet upwind on the starboard quarter of the DD-592 with her bow into the wind (Figure 2.2). Ship movement probably took place during the first 20 minutes after zero time; however, the DD-474 GITR records for Umbrella suggest that the ship did not move very far from its original position during the first 5 minutes. All target ships were equipped with full washdown, which was started at the time of final evacuation (H~4 hours on Wahoo and H—2 hours on Umbrella) and was fueled to run 14 hours. The washdown systems operated as planned, with the single exception of the System on the DD-474 during Shot Wahoo. This ship did not appear to have washdown operating forward at shot time. 3.4.1 Gamma Dose Rate versus Time. Because of a mutual interest in the gamma radiation fields aboard the three destroyers, Projects 2.1 and 2.3 both used the records obtained by the weather deck GITR’s at the bow, amidship-port, and amidship-starboard positions. Project 2.1 obtained dose rate information from these instruments, using the 704 computer on Parry Island rather than the GITOUT device used for the coracie records. Since the two methods of readout are entirely compatible, the information obtained by Project 2.1 has simply been recast by this project into a form identical to that used for the coracle records. In brief, the 704 program, described in References 57 and 86, is identical to the timebetween-pulse method described for the GITOUT device. Onlythe initial rise in dose rate on the low-range channel and the subsequent high-range channel record were read outy using the 704 computer. The timing channel on the shipboard tapes was first monitored to detect possi- 276 Page 277 was deleted.