The CRF is determined from the appropriate nomogram dependent upon the known decay exponent.
These nomograms show the relationship of CRF, n, time of entry (Te), and time of exit (Tx), where time
of exit (Tx) = Te + time of stay (Ts). The time after burst for Te and Tx is scaled along the curve for
each decay exponent. Figure 1-9 gives the CRF for decay exponents below standard (Low n) and Figure
6-10 gives the CRF for decay exponents above standard (High n). The CRF is found by placing a
hairline on the time after burst curve for the known decay exponent, so that it passes through the Te and
Tx points. The CRF is read at the point where the hairline intersects with the CRF scale. In the example
shown in Figure 6-11, Te = H +2, Tx = H + 10, the hairline intersects the CRF scale at 0.44. With this
CRF (0.44), you would multiply the total dose computed on the total dose nomogram.
CM2308
6-24
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