with time, and the lower broken line indicates the Rare value.
An in-
spection of tnese curves shows that oa description of the events oceurring within 48 hours will define most of the provlem.
By 4d hours
almost 50% of the infinity dose has been received end the added daily
increment following this is sufficiently smali so that no change in
lethality estimates need be made for short additional exposures.
These
statements are also true even if the calculations are based on the lower
dashed line which takes into account the factor of biological recovery,
using a 10% per day recovery rate.
Thus, if there are methods avail-
able for protecting personnel during the early hours following arrival
of fall-out, the greatest potential damage will ve avoided.
In applying this type of analysis to idealized fall-out iscdose
contours, it is important to realize tne significance of the figures
used.
These are figures applicable to a person standing unsnieided in
a level radiation field.
It has been estimated=/ that the open field
dose may be less vy a factor of about 0.70 than the theoretically calculated dose for a smooth infinite plane surface, and that for designed
shelters virtually complete protection could be provided.
In a situation where adequate shelter is availavle, control of
dosage is possivle ty limiting the amount of time spent outside the
shelter.
With adequate early protection, fieids which head very high
4nitial dose rates may eventually be entered safely from shelters, with
longer and longer exposures being possible as the field continues to decay.
However, the field radiation levels at later times way still ve high
enough to constitute a hazard and the rate of fall-off ma; be sufficiently slow so that little time can be spent in the area without incurring
risk.
Existing conditions must be weighed in evaluating the potential
hazard.
Application of Physical Contour Lines to Lethality Expectations.
In order to assess the significance of the physical fall-out
measurements and contour line diagrams, these must be translated into
21/
Hill, J.E., Effects of Environment in Reducing Dose Rates Produced
by Radioactive Fall-out from Nuclear Explosions, The RAND Corp.,
R.M.
-
1285-1,
1954.
7G