3 <t<10hrs
10<t<48hrs
= -1.19
k= -0.815
4&8 <t<480hrs k= -1.50
:
1s
a
‘
. ades
1 2
Vr a
ud
fe
Figure | depicts thiesseesy in comparison to t °““,dwemmtoractabte-demey of this
type aeconsistent with the presence of Np-239 (t,=56 hr) and U-240 (ty=14 hr),
significant neutron-activation products of the U-238 in a thermonuclear device.
’
frais
Because, fallout decay rate data on Rongerik Atoll are not available, dose
calculations for awe-military personnel on Rongerik are made using the measured decay
rates on Bikini and the measured radiation intensity on Rongerik Atoll (280 mR/hrat
D+9 days).
In addition, the radiation environment during fallout deposition must be
more explicitly defined.
From the gamma background monitoring instrument on
Rongerik, the time of arrival of measurable fallout fron{
Brav £2 RZen determined to,
be 1407 hours, or 7.4 hours after the shot. The radiation time-intensity recordings on™
Bikini indicated that, once fallout began, a period of 1-2 hours elapsed while fallout
was occurring before the radiation levels reached a maximum and began to decay,
even though fallout was still continuing (Reference 7).
Other data were obtained
aboard three Task Force 7.3 ships that were positioned at various distances downwind
from the BravoGZ.
On one of these ships--the
GYPSY--fallout
commenced
approximately”7 hours after detonation, about the time of arrival on Rongerik.
The
GYPSY data indicated that at least 4 hours of significant fallout occurred. The exact
duration cannot be determined because ship washdown procedures were initiated while
the intensity was still increasing.
The data indicate, however, that at locations
downwind from Bikini, the time to maximum intensity was somewhat longer than it
was on Bikini. Based on these data, a five-hour period of significant fallout deposition
is used to characterize the radiation environment on Rongerik. It is assumed that 90
percent of the fallout, by mass, was deposited during this interval.
/O