(9) Stay time.
The period during which personnel
remain
within
a
particular
area
of
contamination or radiation hazard.
(10) Turn-back dose.
A radiation dose, determined by the command prior to a survey, at which
personnel must turn back to avoid exceeding the operation exposure guidance.
(11) Turn-back dose rate.
A radiation dose rate, determined by the command prior to a survey, at which
personnel will turn back to avoid undue exposure hazard.
2.
Decay Nomogram.
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 5-1 on page 5-9, 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 (n = 1.2) of decay. 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.
Use of the decay nomogram, involving standard decay, (1.2), is shown in the
examples below.
Example problems. In working with nomograms, care should be taken to be as
consistent as possible when joining values with the hairline. Be sure that
the hairline intersects the vertical line and the interpolated value (tick
mark) as closely as possible.
Dose-rate values smaller or greater than
those shown on the nomogram in Figure 5-1 may be reported. In the case of
smaller values, multiply the dose rate by 10, proceed with the calculation,
and divide the resulting dose rate by 10, see Example Problem 4.
In the
case of greater values, divide the dose rate by 10; proceed with the
calculation, and multiply the resulting dose rate by 10.
When using this
process, NEVER multiply or divide a number from the time scale; multiply or
divide, as appropriate, using only the dose rate values, see Example Problem
5.
CM5206
5-6
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