Once the average n has been determined, the decrease in the radiation dose rate from a single explosion
can be calculated by the use of a nomogram. The residual radiation decay (fallout) nomogram (Figure
6-5) allows the user to find the dose rate at any time if a dose rate at a known time after the burst is
available.
This nomogram contains 4 lines of 2 scales each which denote time after burst (in hours) for
nonstandard decay exponents as indicated above each scale and 1 line (the index scale) which denotes
time after burst (in hours) for the standard rate of decay (n = 1.2). The R1 scale, at the right of the time
scales, shows dose rates at H + 1; 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. In
using this nomogram for decay exponents other than standard (1.2), the times from the various decay
exponent scales must always be projected to the index scale before pivoting. The examples on pages 6-
12 through 6-14 explain the use of the nomogram for decay exponents other than standard.
CM2308
6-10
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