becoming prohibitively high causing the total dose to approach the operation exposure guide, prior to
reaching this maximum dose rate point, the commander may elect to change the route of advance or
withdrawal, depending upon the tactical situation.
Routine occupancy of an area of induced radiation is possible 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 an induced radiation field, the
dosimeter should be checked frequently.
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 produced in the burst. The soil composition is the most important
factor in the decay of induced radiation. Since the actual soil composition will not normally be known,
Soil Type II has been chosen as standard 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.
a. Decay Nomograms.
The decrease in the radiation dose rate can be calculated by the use of a nomogram. The residual
radiation decay (induced) nomogram, Figure 6-12 allows the user to predict the dose rate at any time, if
a dose rate at any time after the burst is available.
The nomogram (Figure 6-12) contains four scales which denote time after burst (in hours) for four Soil
Types (I, II, III, and IV), as indicated above each scale. The scale for Soil Type II is indicated as an
index scale and will be used in calculations when the soil composition is not known. The R1 scale, at
the right of the time scales, shows dose rates at H + 1; the Rt scale, at the left of the time scales, shows
dose rates at times other than H + 1. The outside left and right lines are reference lines to be used in
aligning the hairline.