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ciated with the prediction of fallout from row-charge subsurface nuclear detonations are discussed. This paper is limited to research or
development in which the investigator has been personally involved
within the Plowshare Program of the Lawrence Radiation Laboratory.
CRATERING FALLOUT MODEL
Basis of Model Construction
For prediction of the area affected by radioactive fallout from a
subsurface detonation of a nuclear explosive and of the gross external
gamma dose rate in the surface-fallout pattern, knowledge of the following factors are needed:
1. The heights of the base, the top, and the radius of each radioactive cloud (i.e., the main cloud and the base surge) formed by the
detonation at the time the clouds cease to rise in the atmosphere. This
time is defined as the time of cloud stabilization. The cloud heights are
prescribed in terms of height above surface zero.
2. The total yield of the explosive, W_; the fission yield of the explosive, W,; the depth of burial of the explosive, z; the fraction of the
fission-product gamma emitters expected to appearin the fallout pat-
tern beyond the estimated radius of direct ejecta, F.; and the equivalent
fission-yield gamma needed to simulate the gamma dose from induced
activities.
3. The activity—particle size distribution in both the main cloud
and the base surge and the fraction of F, in each.
4, The terminal fall velocity of the fallout particles (in still air)
as a function of particle size and height in the atmosphere.
5. The time and space prediction of the horizontal wind at the level
of each cloud top along with the specification of the wind-shear tangential and normal to the wind for the layer through which particles fall.
This knowledge is required because in a fallout calculation involving
two clouds (main cloud and base surge), the calculation of the fallout
pattern for each cloud is done separately. The total surface-fallout
pattern of the shot is found by summing the patterns from the base
surge and the main cloud.
6. The effect of horizontal eddy diffusion on the growth of the
horizontal radius of the disks of radioactive particles as the disks
fall earthward. The initial debris cloud is subdivided into disks of
debris in the model as a function of initial height in the cloud and of
particle size.
The preceding information (items 1 through 6) provides the simplest, but still adequate, basis for constructing a ‘cratering fallout
model. In addition to this information, it is assumed that the fission-