PREDICTION OF SUBSURFACE-DETONATION FALLOUT
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ALLUVIUM
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Fig. 3g—Main-cloud height as a function of the total yield and the pa-
rameter z/Da.
cloud-geometry data from high-explosive and nuclear-explosive detona-
tions conducted by the U. S, Atomic Energy Commission in alluvium
and basalt. Implicit in the summary is the assumption that a high explosive and a nuclear explosive detonated in the same material at identical depths of burial and under similar meteorological conditions produce the same cloud geometries.
Activity—Particle Size Distributions
In a typical subsurface nuclear detonation in alluvium, two clouds
are formed, The main cloud is composed mostly of vented cavity gas
and particulates (originating from either condensation or injection and
entrainment of soil). The base surge is composed of ejecta and suspended fine particulates. For a nuclear cratering shot in alluvium, it
is assumed that 80% of the F, gammaactivity is in the main cloud and
20% is in the base surge. The 0.8 F, main-cloud activity is assumed to
be subdivided between two lognormal activity—particle size distributions. The first activity—particle size distribution contains the activity
0.8 w,(1)F, and is characterized by the mean In r,,(1) and the standard
deviation o,,(1). The second activity—particle size distribution contains the activity 0.2 w,,(2)F, and is characterized by the mean In r,,(2)
and the standard deviation o,,(2). The activity of the first distribution
is assumed to be homogeneously mixed through the whole main cloud,
whereas that of the second distribution is assumed to be homoge-