little differential effect is to be expected from a lamina of activity on top of the 2 inches of sang versus activity distributed on the honeycomb insert and bottom of the tray. The more serious possibility of the active particles sifting down through the inert sand appears not to have occur~ red, because the survey-meter ratios of AOC,-B’s to OCC’s taken at Site Nan, Site Elmer, ang NRDL did not change significantly with time. ) In Table 4.5, weighted-mean platform values, obtained as described above, are converted to fissions per square foot and compared to the average buried-tray deposit taken from Table B27, It may be seen that, within the uncertainty of the measurements, the weighted-mean platform values are in good agreement with the ground results. It must be recalled, however, that single winds prevailed at How Island for all shots, and that the observed bias ratios were low (< 2). The AOC,collections at Station K (Table 3.15) are also included in Table 4.5 for comparison, - They appear to be consistently slightly lower than the other determinations, with the exception of the much lower value for Shot Navajo. The latter may be due to recovery loss and counting error resulting from the light fallout experienced at the station during this shot. Because only one collector was present in each minor sampling array, bias studies of the kind conducted for the major arrays were not possible. As mentioned earlier, however, an attempt was madeto minimize bias in the design of the collector and, insofar as possible, to keep geometries alike. Although it was necessary to reinforce their mounting against blast and thermal damageon the rafts and islands (Figure 2.7), identical collectors were used for all minor arrays. Shipboard Collections and Sea Water Sampling. The platform collections of the YAG 39 and YAG 40 may be compared with the water-sampling results reported in Reference 20, decay-tank data from the YAG 39, and in some cases with the water-sampling results from the SIO vessel Horizon (Reference 15). Strictly speaking, however, shtpboard collections should not be compared with post-fallout ocean surveys, because, in general, the fallout to which the ship is exposed while attempting to maintain geographic position is not that experienced by the element of ocean in which the ship happensto be at cessation. The analysis of an OCC collection for totai fission content is straightforward, although the amount collected may be biased; the ocean surface, on the other hand, presents an ideal collector but difficult analytical problems. For example, background activities from previous shots must be known with time, position, and depth; radionuclide fractionation, with depth, resulting from leaching in sea water should be known; and the decay rates for all kinds of samples and instruments used are required. Fallout material which is fractionated differently from pointto-point in the fallout field before entry into the ocean presents an added complication. Table 4.6 summarizes the results of the several sampling and analytical methods used. The ocean values from Reference 20 were calculated as the product of the equivalent depth of penetration (Section 3.2.5) at the ship and the surface concentration of activity (Method I). Thelatter was determined in every case by averaging the dip-count values of appropriate surface samples listed in Table B.32 and converting to equivalent fissions per cubic foot. When penetration depths could not be taken from the plots of equivalent depth given in Figure B.1, however, they had to be estimated by some other means. Thus, the values for both ships during Shot Zuni were assumed to be the sameas that for the YAG 39 during Shot Tewa; the value for the YAG 39 during Shot Flathead was estimated by extrapolating the equivalent depth curve, while that for the YAG 40 was taken from the same curve; and the values for the YAG 40 during Shots Navajo and Tewa were estimated from what profile data was available. The conversion factor for each shot (fissions/(dip counts/min at 200 hours) for a standard counting volume of 2 liters) was obtained in Method I from the response of the dip counter to a known quantity of fissions. Although direct dip counts of OCC aliquots of known fission content became available at a later date (Table B.15), it was necessary at the time to derive these values from aliquots of OCC and water samples measured in a common detector, usually the well counter. The values for the decay tank listed under Method I in Table 4.6 were also obtained from dip counts of tank samples, similarly converted to fissions per cubic foot. Dip-counter response was decay-corrected to 200 hours by means of the normalized curves shown in Figure B.14. Another estimate of activity in the ocean was made (private communication from R. Caputi, NRDL), using the approach of planimetering the total areas of a number of probe profiles meas- 118