[ RadSafe ] hand held meters

[Dan McCarn]

Hi John & Group:

Perhaps it is not well known that instruments can be modified quite easily
by the manufacturer to have different integration times. For the Ludlum
Model 19 and it's ilk, it's basically a change in a couple of capacitors.
 I had one of my instruments changed in that way as well as adding an
Analog-to-Digital Converter (ADC) inside the instrument with an external
USB port.

Dan ii

Dan W McCarn, Geologist
108 Sherwood Blvd
Los Alamos, NM 87544-3425
+1-505-672-2014 (Home – New Mexico)
+1-505-670-8123 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email) HotGreenChile at gmail dot com


On Thu, Jan 23, 2014 at 7:54 AM, Dixon, John E. (CDC/ONDIEH/NCEH) <
gyf7 at cdc.gov> wrote:

> 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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