Figure 8 is a useful plot for facilitating time-of-stay calculations.
Perhaps the best way to explain the method of employing this
set of curves is to cite an example.
Assume that an individual enters
e contaminated area 12 hours after detonation and the reading at this
time is 5 roentgens per hour.
As planned for the operation, it will be
necessary to stay in the area 3 hours.
Thus, on the horizontal axis,
select the time 12 hows, read vertically to the intersection of the
3-hour curved line. Read the vertical axis, as indicated D/R. This
value of 2.6 is multiplied by the radiation intensity, 5 r per hour, to
give 13, which is the total number of roentgens received during the
period of the stay in the area.
The scaling of residual radiation contours is not a simple process
because of the many variables involved.
In addition, changes in cloud
models and in mechanisms of deposition occur with changes in yield and
in wind velocity.
For example, the tropopause layer in the atmosphere
has a slowing down effect on the rise of an atomic cloud through it,
with the result that atomic clouds which reach this layer tend to
flatten out against it, as though against sa ceiling.
The result is
that such clouds are broader, and their fall-out deposition patterns
are wider and shorter, than would be the case from an identical detonation whose cloud did not reach the tropopause.
A valid and ideally
useful scaling process should be easy to apply and should be based on
a conservation of material assumption, since it is obvious that the
scaling process should not cause more material tofall out than is
available.
One such method is "cube root scaling", by which linear
contour dimensions are scaled as the cube root of the ratio of yields
and areas as the two-thirds power of the ratio of yields, with simultaneous scaling of contour dose rate values as the cube root of the yield
ratio.
This method conserves material, in that the percentage of
available material brought down within each scaled contour remains con-
stant. It is also easy to apply.
However, it is subject to the inher-
ent inaccuracy discussed above and common to all residual radiation
scaling methods developed so far:
it does not allow for the changes
39