[ RadSafe ] hand held meters

Thu Jan 23 09:45:02 CST 2014

Thx  for all the  help on the handheld meters.  It looks like we have an 
approach for our particular problem, but since this is for a client, the 
details aren't "available for publication."  However, the advice and 
feedback made it pretty clear that low dose rate measurement outdoors is 
an art not a science, so we're basically going with a two stage approach. 
First stage is a go/no go survey with a conservative decision level.  If 
the decision level is exceeded, the client will call in the experts for a 
second stage. There will probably be a fair number of false positives, but 
that seems to be acceptable.

Again, thx.  RADSAFE has once again proven to be solid resource.  Hope to 
return the favor on questions where I think I might know something useful 
;-)

 - - jmr

John Rich
312-269-3768

From:   "KARAM, PHILIP" <PHILIP.KARAM at nypd.org>
To:     "The International Radiation Protection (Health Physics) Mailing 
List" <radsafe at health.phys.iit.edu>
Date:   01/23/2014 09:26 AM
Subject:        Re: [ RadSafe ] hand held meters
Sent by:        radsafe-bounces at health.phys.iit.edu

John -

Very good advice. It's also worth mentioning that many of the NaI-based 
microR meters are energy-dependent, so their readings can be off 
substantially. We did a test along with NYS DOH an USEPA, using a 
NaI-based detector side-by-side with a pressurized ion chamber at a site 
contaminated with thorium. The NaI detectors (we used two or three 
different brands) all came in with readings that were about half of what 
the PIC registered. The reason, of course, is that the NaI detectors 
over-responded to the low-energy gammas from the Th decay series.

So I concur - a PIC is a far better way to measure low levels of radiation 
compared to either GM or NaI. 

Andy

-----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

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [
mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of 
JOHN.RICH at sargentlundy.com
Sent: Tuesday, January 14, 2014 3:19 PM
To: radsafe at health.phys.iit.edu
Cc: EDWARD.L.MARTIN at sargentlundy.com
Subject: [ RadSafe ] hand held meters

radsafers

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 
mR/hr.
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
312-269-3768
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