[ RadSafe ] Fwd: hand held meters

Chris Alston achris1999 at gmail.com
Tue Jan 14 16:51:35 CST 2014

Hi John

I think that we need to ask you to be a little more specific as to
your application.  So, for instance, what would you be looking for?
E.g., interesting variations in background, deposits of uranium ore,
subject of your choosing here_____________________.

Generally speaking, NaI scintillometers are much more sensitive and
faster than GM meters; but the time to "return to background" from a
random spike is essentially immediate, if you are listening to an
audio output.  Of course, you cannot tell that until you perceive the
longer interval between clicks, or the lower frequency of a tone.
Then, on many meters, one can select the response time constant of the
visual indicator of dose rate or event count rate, on others it is
preset for each range of the instrument.  A "short" time constant
might be 0.5 - 2 seconds, a "long" one might be 5 - 22 seconds.  In
this context, "response time" usually means something along the lines
of how long it takes for a meter's needle to go from 10% to 90% of a
final reading.

Hope this helps a little.  It sounds to me like you might want to demo
a couple of instruments, to see what works for you.

---------- Forwarded message ----------
From:  <JOHN.RICH at sargentlundy.com>
Date: Tue, Jan 14, 2014 at 3:18 PM
Subject: [ RadSafe ] hand held meters
To: radsafe at health.phys.iit.edu
Cc: EDWARD.L.MARTIN at sargentlundy.com


We're looking for practical experience on using hand held monitors in an
outdoor setting.

The background gamma dose rates in the area are about 0.02 mR/hr.
The expected change that we want to see is from about 0.02 mR/hr to 0.04
So the dose rate goes from about 0.02 mR/hr to 0.04 - 0.06 mR/hr. (two x
background to 3 x background)

The questions are:
(1) what kind of hand held monitor would be good to see this change (e.g.,
PIC, GM tube, scintillation detector, etc.)?
(2) since this is outdoors, how long should the surveyor wait for the
readings to stabilize after a random spike?.

I asked a similar question earlier,  and the consensus seemed to be that
making these measurements with a hand held monitor was problematic. My
personal experience in this area is very limited, but it seems like the
spikes could reach about 0.01 mR/hr and lasted several seconds.

thanx in advance  - -jmr

John Rich

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