would be 1; on the other hand, the resultant vector would vanish for a wind that rotated uniformly around the platform an integral numberof times during uniform fallout, and the fraction would -be 0. . Where necessary, the mean value of the four OCC and two AOC, collectors was chosen as representative for a platform; but when a curve of fallout amount versus angular displacement from the bias direction could be constructed using these collections, the mean value of the curve was obtained from 10 equispaced values between 0 and 180 degrees. The latter applied to all ‘platforms except the LST 611 and the YFNB’s, probably indicating disturbances of the air stream ‘incident on the platform by the geometry of the carrier vessel. These platforms, however, were mounted quite low; while the YAG platforms were high enough and so placed as to virtually guarantee undisturbed incidence for all winds forward of the beam. * Pertinent results are summarized in Table 4.4. Fallout amounts per collector are given.as doghouse-counter activities at 100 hours, convertible to fissions by the factors given in Table B.13; the mean values so converted appear in Table 3.15. Wind velocities are listed in Table -B.37; as in the summarytable, the directions given are true for How Island and relative to the bow of the vessel for all other major stations. No attempt was madeto account quantitatively for the values of the bias ratio observed, even for a single-wind system; undoubtedly, the relative amount deposited in the various parts of the platform depends on somefunction of the wind velocity and particle terminal velocity. As indicated earlier, the airflow pattern induced by the platform itself appeared to be reproducible for a given wind speed, and symmetrical about a vertical plane parallel with the wind direction. Accordingly, for a given set of conditions, collections made on the platform by different instruments with similar intrinsic efficiencies will vary only with location relative to the wind direc- tion. Further experimentation is required to determine how the collections are related to a true ground value for different combinations of particle characteristics and wind speeds. A limited study of standard-platform bias based on incremental collector measurements was “also made, using the data discussed in Section 3.2.4 (Reference 19). These results are presented in Figures 4.12, 4.13, and 4.14. The first compares particle-size frequency distributions of collections made at the same timeby different collectors located at the samestation; studies _for the YAG 39 and YAG 40 during Shots Zuni and Tewa are included. The second compares the total relative mass collected as a function of time, and the variation of relative mass with particle size, for different collectors located at the same station; as above, YAG 39 and YAG 40 collections during Shots Zuni and Tewa were used. The last presents curves of the same type given in Section 3.2.4 for the two IC’s located on the upwind side of the YAG 39 platform; these may be compared with the curves in Figure 3.8 which were derived from the IC on the downwind Bide, The results show that, except at late times, the overall features of collections made by dif‘ferent instruments at a given station correspond reasonably well, but that appreciable differences in Magnitude may exist for a particular time or particle size. In the case of collections made on a single platform (YAG 39), the differences are in general agreement with the bias curves discussed above; and these differences appear to be less than those between collections made near the deckand in the standard platform (A-1 and B-7, YAG 40). It is to be noted that incre- mental-collector comparisons constitute a particularly severe test of bias differences because the small size (~ 0.0558 ft?)of the collecting tray. How Island Collections. One of the primary purposes of the Site How station was to determine the overall collection efficiency of the total collectors mounted in the standard ‘Platform. An area was cleared on the northern end of the island, Platform F with its supporting tower was moved from the YFNB 13 to the centerofthis area, and 12 AOC, trays were filled With local soil and buried ina geometrical array around the tower with their collecting surfaces flush with the ground (Figure 2.8). After every shot, the buried trays were returned to NRDL and counted in the same manner as the OCC trays from the platform. It is assumed that the collections of these buried trays represent a near-ideal experimental 4Pproach to determining the amount of fallout actually deposited on the ground. (Somedifferences, believed minor, were present in OCC and AOC,-B doghouse-counter geometries. Very t 117