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
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1
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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.