Re: pancake probe to mr/hr conversions -Reply

[Keith Welch <welch@CEBAF.GOV>]

At 08:20 AM 8/29/96 -0500, you wrote:

Brian/Dave

When I did pancake probe calibrations (not at a DOE lab either) we actually
used a conversion like this (instead of pulsing it) to calibrate the meter
on all EXCEPT the X1 scale.  We used Co-60, and actually set up the probe in
the appropriate field and adjusted it to read the count rate corresponding
to the known exposure rate.  I'm not sure, but I think the number was
derived from a combination manufacturer's suggestion and experimentation
with instruments to determine a valid number.  Our conversion was  3300 cpm
= 1 mR/hr (or 3.3 cpm= 1uR/hr). On the lowest scale (the one usually used
for frisking), we did a pulser set up and then verified with a calibrated
source that 1000 dpm (Co-60) would give a count rate of ~ 100 cpm.

By the way, Dave, Eberline gives some conversions like the one you mentioned
in their manuals for instruments (eg. SRM-100, ESP, etc) - but they are
specific to the probe and usually reference Cs-137 as the source.

K. Welch
welch@cebaf.gov

>>>> Brian Rees <brees@lanl.gov> 08/28/96 04:16pm >>>
>At the last place I worked (not a national lab), we always "calibrated" our
> pancake probes (thin window GM tubes for those so inclined) to obtain
>a  conversion factor in case a technician came across something
>unexpected and  didn't have another instrument.
>
>We usually had a conversion factor of about 4.1 cpm=1uR/hr (Cs-137). 
>This  is subject to quite a few limitations, but when you're working in the
>field,
> a ballpark number is better than nothing.
>
>This is subject to lots of disclaimers, etc, as it has no bearing on my 
>employer.
>
>Brian Rees brees@lanl.gov
>
>
>