PATTERN OF FALL-OUT FOLLOWING BRAVO EVENT ‘ (Combined Analyses - Imnediate and One Week after BRAVO) 1. General. The pattern of ultimate fall-out of radioactive sarticles has been established utilizing in the cases of the most critical area (1.0. ‘ bearing about 050° Trus, clockwise to 120° True from Ground Zero) the followe S rz ings a. Aerial survey by P2V employing NYO0-a5C survey equipment, with readings in ar/hr extrapolated to ground level. be Known ground readings taken at some atolls (early and later) used with their time and intensity (actual observations) to get a Seeling for the overall situation. Ce Resultant wind pattern to establish best wind for period froa 3 minus 1 hour (USS CURTISS Observation - BIXINI) to BH plus 8 hours (Rengeriz sounding) together with the H minus 34 hours (Rongerik 0300) to piece cogether 100,000 feet) for which there sere available winds to 95,000 feet, and with the assumptions listed below in constructing shadows (fall-out) of stem and mushroom, there are obtained 2 areas - elliptical inshape, generally east of Ground Zero and superimposed on each other (Appendix I). The suggesved Zallout area (blue) for the stem is oriented about 070° True from point SB of Ground Zero, distant 35 miles and with a 200-mile major aris, 100-2ie sizor axis with a series of extremely hot elliptical envelopes ezanating ‘roa Ground Zero out to about 110 miles. Superimposed on this area (red) is «he siggested moshroom fall-out pattern which is an ellipse oriented 080° True, 49 ailes from Ground Zero, major axis at least 180 niles, zincr aris 45-90 sites. It is assumed thatthe cloud dianeter in the sushroon for the period ic >sest‘ion was at least 70<100 miles. This shows therefore, that the early Sa---c=: at Rongerik could eome easily from the nushrooz - large pazzicles oy = fics & hours, and since‘ the superimposed fall-outs fre stem and susnrocs cross <6 northern half of Rongelap Atoll, one would expect these islancs <2 Se ex-ceecon ingly high with their radiation levels, This sight be likened to scavenging of the hot stem material by large particles Sro=z the tropopause anc a>cve. However, the major hot fall-out elenent must coms from <ne stea debris. The assuaptions used in the rough constrzction of the ellipse fem che whole cloud ares (LtCol Iulejian report on Fell-out - ARDC, SECAET, RD): . Inclosure 6 eee 1 | ee om fh ke awe eee ee would make cloud arrive at Rongerik at about © plas 12 hours. Zowever, by che method of plotting the entire clond height (which is believed to de a>cut te difficulty in making fall-out arrive from the stem of the atomic cioud (o- 55,000 feet-tropopause) at Rongerik in 8 hours. The 10.4 miles/hr above vim de Since the Rongerik (NYOO-aZC) survey meter trace established initial time of arrival of fall-out, this time was used in coordination with resultant wind at the cloud level which passed over Rongerik. This level was _ 25,000 feet vector. Its average speed from Ground Zero calculated froa resultant wind plot vas 10.4 miles/hr. At first, there was considerable - the wind pattern above the tropopause.