4.1 WATER SAMPLES While the land and reef collections were be.ng rrade, the M-boat that had transported the field crew from the USS Oakhill to the collecti-.g station was used for dredging, plankton towing, and water collecting in contiguous waters. Be->ause of the expected difference in specific ac- tivity, the volume of the preshot water samples was 6 liters, and that of the postshot samples was % liter. The samples were collectea with a Foerst type water bottle. 4.1.1 — Sample Preparation Since it was impractical to bring 6-liter water samples to the laboratory for processing, a precipitation method was used in the field for the preshot samples, and only the precipitate was returned to the laboratory for counting and analysis. The procedure used in the field was determined from experimentation in the laboratory with “spiked” sea-water samples and, in general, was a double-precipitation process in which most fission products were brought down ina ferric hydroxide scavenge. Calcium and strentium were precipitated as oxalates. The specific procedures are outlined in Appendix H. ye Tat 4.1.2 Results Results are presented in Table 4.1. Note that the values in this table are in terms of milliliters of water samples and that the disintegration rate is as stated and not in thousands as has been used in other tables ir. this report. Also the values for both the Fe(OH); scavenge and the Ca-Sr oxalate, even though small, have considerable reliability because the values have been based on large samples. The total sample activity was divided by the number of milliliters in the sample, which was 6C00 for the pretest samples and 500 for the posttest samples. The values for whole sample (postshot) were based on 2 3-ml sample that was withdrawn before precipitation; hence it would be expected to be less reliable. From inspection of Table 4.1 the foliowing conclusions can be drawn: For the pretest samples radioactivity of the Bogombogo sample was considerably greater than that for other stations. Why it was greater is not known, but the activity of plankton samples was also greatest from this station. There were smali but measurable amounts of activity in water samples from other stations. For the posttest samples the amountof activity was closely and inversely related to distance of sample from test site. For stations nearest the test site values for the posttest samples were several hundred times greater than those for the pretest samples. Since the counts of Fe(OH), scavenge and Ca-Sr oxalate do not equal the count of whole sample, evidently all the radioactive materials were nct removed by these processes. A rain-water sample was collected 33 hr after Mike shot in the lagcon off Eniwetok Island. eo. A 450-cc sample was evaporated and counted on Nov. 4, 87 hr after Mike, using a Victoreen survey meter with a 1-in. end-window tube, the window thickness being 1.8 mg/sq cm. The maximum count was 10,000 per minute. 4.2, PLANKTON The plankton nets were 0.5 m in diameter and 2 m long. The anterior section was cylindrical, and the posterior section was conical with a detachable net end. The plankton tows were made in pairs at the surface during daylight hours. One net of each pair was constructed with No. 6 silk (74 meshes/in.) and the other of No 12 silk (173 meshes/in.). Towing time was usually 1 hr, and the towing distance was about 1% miles. Catches of plankton were small. Exclusive of jellyfish, the greatest volume of plankton in a 1-hr tow was 28 cc. Thic value was obtained by decanting and measuring the preservative and then subtracting this amount from the volume of preservative and plankton. js 27 UNCLASSIFIED . -