METEOROLOGY—FALLOUT AND WEATHERING
By Lesrer Macnra and Kenneru M. Nacuer
US. Weather Bureau, Washington, D.C.
INTRODUCTION
locus of points at which particles from a given
Meteorology plays two roles in the study of
the biological effects of nuclear radiations on
on the chart. Further, from the same informstion, it is also possible to derive the locus on
man.
First, winds and rain govern the trans-
port of the fission products to man’s environment. Second, after settling on the ground,
the fallout particles can have their effects modified by rain washing and wind erosion. It is
the purpose of this paper to discuss both roles.
Research in the Weather Bureau has been devoted largely to the first problem, namely predicting the fallout. Accordingly, in the absence
offirst-hand research, the discussion of weath-
ering will be more goneral.
TRANSPORT
There are two aspects of the problem of pre-
dicting dosages of radioactivity on the ground.
In the first: place, the initial distribution of
radioactivity in the stabilized atomic cloud on
various particle sizes, at different altitudes must
be given. Then, with this distribution as the
altitude will fall.
These are the radial lines
the ground of particles of the same size (or,
really, fall rate), also shown on the figure and
labelled according to their diameters in microns.
The heavy line shows the path that the 100micron particle takes in falling from 40,000
feet to the ground. The heavy dashed lines
are isolines of observed radiation intensities,
in milliroentgens per hour 12 hours after the
burst.
Although the actual procedure is more
complicated because of the finite lateral width
of the cloud, the theory of producing a model of
cloud radioactivity can be illustrated from this
figure. The procedure is that of associating
the amountof radioactivity at a given range of
cloud altitude and particle size with the corresponding radiation intensity on the ground.
For example, the particles in the shaded area
(those between 87 and 100 microns in diameter
which were initially between 30,000 and 35,000
In theory, it might be possible to deduce the
distribution of radioactive particle sizes and
feet) have caused an average dose rate of about
50 mr/hr. It is to be noted that this mapping
procedure bypasses the determination of the
number of radioactive particles and their
specific activities, In fact, since the radiation
js necessaryto rely on the findings from previous
ground with conventional hand radiationmeasuring instruments (or, less frequently, by
starting point, the particles are tracked downward according to their settling velocity and
horizontally according to the winds.
their specific activities in the atomic cloud from
the explosion kinetics, thermodynamics, and
available scavenging agents, but in practice, it
nuclear explosions.
Figure 1 shows, in principle, how this is
accomplished. From considerations of the
settling speed of the particles and the winds,
it is a straightforward process to obtain the
intensity lines used in this type of analysis are
obtained for Nevada tests by monitoring the
aircraft surveillance), the effectof shielding due
to rough terrain is already included in any
forecast derived from such information. This
technique of preparing forecasts of radiation
intensities from cloud models is now used by
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