The mixing of the radiow-tive m terial in the oc eon will des reese the amouat of gamma flix
which may be measured in the air. raft. Mf the survey is mad) soon after fall ot ceases, this
mixing will not be cou plete.
On +1, Shot Tewa, the 0.235 mr/he contour cateided nearly 2uy
miles west and northwest of Bikini.
The surve, on D+2 placed the end of this isodose pattern
closer to ground zero. The aerial flight surveyed the fallout are. approximately 6 hours aft:
the fallout, and mixing was apparently act completely uniform to the thermoclire. By the new
day some 30 hours had elapsed, much of the mate rial had beca rer.aved from the surface, and
ois expecta that the mixing wis more mearly untorm, as repre .cuted by the data described in
Appendix D.
The area enclosed by a particular contour appears to be stable for a relatively long period of
tie, The 2.5 mr/br isolose after Shot Tewa was followed for scveral days. While the effect
TABL:
412
Shot
FALITO
Total Yield
~
SUMMARY
Shot Site
Ares
{
Mt)” mii?
Tewa
Na@.viss
3.9
Zunt
35
Cherokee
Flathead®
«
wo
Reef
Water
“
Fallout
“met pett_ peti
43,506
10,499
Land
13, 400
Air
Water
None
11,000
|
i
|
:
* Area nit to0 1 mi ‘hr at H+ 24 hours and 3 feet above surface.
ft Bo -ed on 6,450 ne /Mt (Reference 6).
t Based on m. ‘er ial lor ate’ “within the surveyed area, Tables 3.3 through 3.6.
§ Based on exw ripe tated valies, Figures 4.1 and 4.2.
@ Flathead su:.c, limited by aircraft cortaminction.
Results buicd on estimated position
of boundary.
of surface displacement is clearly visible, the enclosed area is approximately the same each day
within the limits of measurement error.
The indications are that the survey results, properly related to mixing in the ocean volume,
may be used fur estimates of fallout density. The oceanographic surveys of Project 2.62 (SIO)
provide more detuiled study of the mixing function.
4.3.2 Estimates of Total Fallout. The fallout distribution from the aerial-survey estimates
are plotted in Figures 4.1 and 4.2. The percentage of the total fission yield is displayed against
the particular boundary isodose contour.
These curves can then be extrapolated to the zero mr
gamma contour and the estimate made of the total amount of fallout in the local area.
The con-
clusions must be applied judiciously, because the estimates are not between measured values,
but an extrapolation beyond the survey area.
The estimates are summarized in Table 4.1. The megacurie summaries represent the material within the EOB of the surveys, and the percentage fallout is based on the percentage of the
total yield found within the surveyed area and on the values extrapolated In Figures 4.1 and 4.2.
Natural radiation background and the residual background from previous shots vary from place
to place. Because small fluctuation in the radiation detector readings are an indication of the
boundary of the fallout, variations in background will affect the outer boundary estimates (Section
1.3.4). While this does not vary the position of the isodose lines, it does affect the position of
the EOB and the estimates contained in the fallout summations.
Of the isotopes produced by neutron activation, two are primarily important in contributing
to the gammaactivity: Np’? and Na”, The Np?*® contribution to aerial-survey measurements
is small, because of the low energy of its gamma photon (Section 1.3.3).
The Na*4 emits high-energy gamma photons and can increase the gamma dose rate measured
by aerial survey appreciably in the period from 5 to 100 hours (Section 1.3.3).
57
Measurabte
Tage sg Deleled.