Re: GM Response (formerly Respect)

[Mike Grissom <mikeg@SLAC.Stanford.EDU>]

Radsafers,

To add to Joel's response, I saw similar detection
efficiencies using the DT-304PDR (Navy guys will
recognize this!) which is a heavily shielded GM
pancake probe.

I posted an item on radsafe a couple of years ago
regarding cleaning up a Bactec vial that had been
broken in a hallway (max of 20 uCi C-14) and in that
exercise (and others in more difficult environments
such as steam autoclaves) we were able (barely) to
find some hot spots off of the floor (some operator
expertise is definitely needed). We, of course,
deconned and swipe surveyed a larger area (beyond the
obvious extent of the liquid spilled). The spots
requiring additional decon/surveying after LSC
analysis of the digestible swipes were exactly
coincident with the hot spots found with the GM. No
doubt we got some help from backscatter to compensate
for the low activity levels present.

I have seen somewhat similar results for S-35 tagged
biologicals on lab bench tops after spills. A thin
window well shielded pancake GM is of low efficiency
for less than 200 keV beta endpoint energies, but
'good enough' to help in these kinds of spills (mCi's
to uCi's). Can't really avoid those swipes though...

Yo for respect!

S.,

MikeG.

At 09:55 AM 9/4/98 -0500, you wrote:
>	RADSAFERS
>
>	I just checked my Ludlum-3 with a Pancake
>
>	I get a "smidgen" (a scientific term if I ever hear one) under 6%
efficiency with a C-14 check source and I get about 8% with S-35.
>...


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