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Submitted 10/31/02 A: The DDSC answer is maybe not. The scan MDC equation in MARSSIM (eqn 6-10) does include a term in the denominator that allows one to account for the probe area. For the case of the floor monitor this would result in a correction term of about 600/100, or 6. However, additional thought was given to this situation, and it is probably not appropriate to correct for the probe area when determining the scan MDC. Current thinking on this matter differs from what is published in the MARSSIM manual.
As
explained in Decommissioning
Health Physics, p. 197, in order to calculate the scan MDC a
certain hot spot size must be postulated. For building surface scans, the
hot spot size is taken to be 100 cm2. This effectively negates the need
for a probe area correction. Indeed, eqn 9.14 in DHP shows the scan MDC
for structures; there is no probe size in the eqn. The size of the
probe (detector) impacts the observation interval - i.e., the time that
the detector has to respond to the hot spot as it is moved over the
surface. So, the only credit that you get with a floor monitor from its
larger probe size is a longer observation interval. That is, the detector
will be over the 100 cm2 hot spot longer for a given scan rate (e.g., 5
cm/s) than would a hand-held detector traveling at the same scan rate.
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