[ RadSafe ] Fwd: hand held meters

[Chris Alston]

Folks

Be sure that your PIC is at thermal equilibrium with the air; until
that is true, you can expect to see readings that are high by as much
as a factor of ten.  Please note that you also will *not* see spurious
readings immediately after a significant change in ambient
temperature.  It is a delayed effect, and dependent on the inherent
insulation of the specific meter.

Cheers
cja
-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Dixon, John
E. (CDC/ONDIEH/NCEH)
Sent: Thursday, January 23, 2014 9:54 AM
To: The International Radiation Protection (Health Physics) Mailing List
Cc: EDWARD.L.MARTIN at sargentlundy.com
Subject: Re: [ RadSafe ] hand held meters
I have looked over most of the posts on this article on RADSAFE. If
you are looking for low background gamma radiation, use a simple
stable instrument. NaI probes are quite sensitive and can exhibit wide
swings in their count rates and obtaining spectra does not seem to be
your goal. I recommend the one instrument which has not received
attention here: the pressurized ion chamber (PIC). There are several
manufactures (Fluke, Thermo-Eberline, etc.). Fluke's can accommodate
very low dose rate levels (uR/hr) and they are digital with slower
response times; however, they give you pretty stable final readings
without the count rate swings a NaI system might give you. If you are
looking to rapidly identify a source of the dose rate level in
question, use a NaI to find where the source is and then use a PIC to
quantify the dose rate level. Wait times for this instrument vary, but
I believe one minute should be sufficient for a reading. Averaging 3
readings might also be a good idea.
Regards,
John Dixon