Re: Response of EDs underwater

[Arthur & Marian Desrosiers <52deerjump@mediaone.net>]

arthur@bartlettinc.com

re:  "EDs do not report under response, low energy photons, radiation
underfoot"

My preference is to use the PDE-4 for all of the above reasons.

1.  The PDE-4 has a sophicated dose calculation algorithm that switches
from pulse counting to measuring resolving time at some dose rate
threshold.  At high dose rates, the resolving time is inversely
proportional to the dose rate.  This prevents the response curve from
folding over the range of dose rates where the instrument is valid (10
microR/h to 100 R/hr).  Naturally, it might fold at dose rates outside
it's range.  The length of the cables affects folding for the exterior
detectors.

2.   By putting five detectors in one U/W box, you have a direct
measurement of dose underfoot if you put one detector on the bottom.

3.   The response of the exterior detectors of the PDE-4 extends into
the low energy range.  But are low energy photons a concern in a water
medium?

If you use EDs to control dose (and use TLDs to measure dose), you know
how the two relate because you have to resolve discrepancies when the
results differ.  You also allow a margin of error corresponding to the
possible difference.

When you send a person down under water, how do you control dose rate
and dose?  Normally you use EDs, set limits, and monitor by computer,
using audible alarms as a backup.  Why not use the ED for the survey, so
you know the expected reponse of the dose control instrument?

Of course, if you are not using EDs to control dose, this line of
reasoning is not valid.

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