(4) Occupancy of an Area.
Routine occupancy of an area of induced radiation is possible in from 2 to 5
days after burst.
In the case of occupancy, low dose rates become of
greater significance. This will be because of the accumulated dose acquired
over the indefinite period of exposure. A commander should seek the least
contaminated region available, consistent with the mission.
During
operations in a radiation field, the dosimeter should be checked frequently.
(5) Variable Decay.
The rate of decay of induced radiation is considerably different from that
of fallout.
The rate of decay of fallout is dependent upon the fission
products produced in the burst itself and can be calculated by using the
Kaufman Equation. On the other hand, soil composition is the most important
factor in the decay of induced radiation.
Since soil composition varies
widely, even in a very localized area, the actual chemical composition of
the soil must be known to be able to determine the rate of decay of induced
radiation. For this reason, four types of soil have been selected to show
the wide variance in the predicted dose rates and decay rates.
Since the
actual soil composition will not normally be known, Soil Type II has been
chosen as standard for decay and total dose calculations. Soil Type II will
be used for all calculations until the unit is advised to use a different
soil type.
3.
Decay and Dose-Rate Calculations.
Soil type is determined by using engineer soil maps or an NBC 4 Report and
the Decay of Induced Radiation Nomograms (Figures 5-6 through 5-9).
The
method is basically a process of elimination. The dose rate and the time it
was measured are applied to a Decay of Induced Radiation Nomogram.
This
will result in an H + 1 or R1 dose rate. Then if the other dose rates and
times from the series report result in the same R1 dose rate, that is the
soil type. If not, check the other nomograms until the one used results in
the same R1.
a. Decay of Induced Radiation Nomograms.
The decrease in the dose rate must be calculated before the total dose can
be found.
This is done with Decay of Induced Radiation Nomograms.
Use
these nomograms (Figures 5-6 through 5-9) for these calculations.
These
nomograms allow the user to predict the dose rate at any time after the
burst. Each nomogram denotes time (hours) after burst for one of the four
soil types.
In each nomogram, the R1 scale is at the right.
This scale
shows H + 1 dose rates. The Rt scale is on the left. This scale shows dose
rates at times other than H + 1.
5-25
CM5206
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