Chapter 1
INTRODUCTION
1.1 OBJECTIVES
The primary objective was to determine the military significance of fallout contamination
from small-yield fission weapons.
The specific objectives were to (1) make the necessary measurements during Shot Fig to
delineate the fallout gamma-radiation field produced by a land-surface detonation of a fission
weapon
(2) use data collected to construct a fallout
model for use with any wind pattern, and evaluate extremes in militarily significant contamination intensities for the same yield range; and (3) define the attendant plutonium contamination problem.
1.2 BACKGROUND
1.2.1 Reason for Fallout Measurements. Small-yield fission weapons (10 to 100 tons)
are being considered for use by the lowest echelons of the Army and Marines. For this
application a minimum of residual contamination, especially windborne fallout, is essential. Ifa serious fallout radiation problem results from a surface burst of such smallyield weapons, it may be necessary to fuze for an airburst, thereby sacrificing obvious
advantages of manufacturing, maintenance, and field use offered by contact fuzing. Estimates of fallout contamination made by extrapolating existing data are questionable.
1.2.2 Estimates from Other Yields. The fallout radiation field that could result from a
surface burst in the 10- to 100-ton range may be estimated from experience gained from
other yields and from the following assumptions: (1) cloud dimensions for the yield of interest can be estimated with reasonable accuracy; (2) vertical space distribution of activity
within the cloud is similar for the yield range involved, that is, the same percentage of
total activity is located within the same relative vertical cloud increment; and (3) at the
same relative cloud height, fall-rate distribution of activity is the same for all clouds.
1.2.3 Fallout Model Used for Test Operations. The vast majority of fallout data has
come from tests on towers at Nevada Test Site (NTS) for the yield range of 10 to 50 kt.
From this experience a fallout mode! has evolved, which consists of vertical space-and-
fall-rate distribution for the activity in the stabilized cloud. By use of this model and wind
velocity predictions for altitudes of interest, expected fallout patterns are calculated prior
to each shot of a test operation as a standard safety practice. Comparison of measured
fallout patterns with those calculated, using best available measurements of actual postshot wind conditions, indicates that intensity and shape of surface contamination are well
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