The mixing of
radioactive material in the ocean will
“ease the amount of gamma flux
which may be measured inthe aircraft. If the survey is maae soon after fallout ceases, this
mixing will not be complete. On D+1, Shot Tewa, the 0.25 mr/hr contour extended nearly 200
miles west and northwest of Bixini. The survey on D+2 placed the end of this isodose pattern
closer to ground zero. The aertal flight surveyed the fallout area approximately 6 hours after
the fallout, and mixing was apparently not completely uniform to the thermocline. By the next
day some 30 hours had elapsed, much of the material had been removed from the surface, and
it is expected that the mixing was more nearly uniform, as represented by the data described in
Appendix D.
The area enclosed by a particular contour appears to be stable for a relatively long period of
time.
The 2.5 mr/hr isodose after Shot Tewa was followed for several days.
TABLE 4.1
Shot
FALLOUT SUMMARY
Total Yield
Shot Site
Mt
Tewa
5.0
Zuni
5
Navajo
Cherokee
Flatheads
Be
-
While the effect
ent
Area*
Fission Yield
mi2
Lie
rt
Reef
Water
Land
Air
Water
Mt
43,500
met
o
10,490
a
13,400
None
in)
11,000
ane
§
S
a
_
Fallout
met
6,458
970
1,540
None
275
pett
24
pets
28
36, 58
50
—_
_—
46
(15
48
23
* Area out to 0.1 mr/hr at H+ 24 hours and 3 feet above surface.
ased on material located within the surveved area, Tables 3.3 through 3.6.
§ Based on extrapolated values, Figures 4.1 and 4.2.
{ Flathead survey limited by aircraft contamination. Results based on estimated position
of boundary.
ns
ic
oF
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 for estimates of fallout density. The oceanographic surveys of Project 2.62 (SIO)
vnd
iter
provide more detailed study of the mixing function.
w
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 conclusions 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.
se
Natural radiation background and the residual background from previous shots vary fromplace
to place. Because small fluctuation in the radiation detector readings are an indication of the
boundary of the fallout, variations in background wiil affect the outer boundary estimates (Section
1.3.4).
While this does not varythe position of the 1sodose lines, it does affect the position of
wae
the EOB and the estimates contained in the fallout summations.
DOE ARCHIV
Of the isotopes produced by neutron activation. two are primarily important in contributing
al
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 Naemits 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). Measurable
37
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