RE: GM Counters in High Backgrounds

["Migliore, Charles W" <Charles.W.Migliore@nspco.com>]

Hi Paul. Long time since we worked generators together at Farley. I think it
was '95 - hurricane Opel outage. Sorry it took me so long to answer, I have
been too busy to keep up with my RADSAFE lately.

You are correct. I had the same discussion with a more experienced
rent-a-tech some time ago, after recording 5000 dpm/100cm2 on a smear survey
counted in a 2000 cpm background (similar 10% efficient frisker probe- 2000
cpm would be an assumed 20,000 dpm background given the same beta 10%
efficiency, but the background was from gamma.) 

I insisted that since the background without the smear was 2000 cpm, to find
the net counts you simply subtracted it from the observed counts (in this
case observed counts with the smear plus background was 2500 cpm.) giving a
net 500 cpm. Well, the proof was in the pudding after we took the alleged
500 ncpm smear to a 100 cpm background and counted it again with the same
instrument..... Surprise, surprise, there were still 2500 cpm on that smear!


Although I was a liquid confectionary poorer, I was nonetheless a wiser
meter swinger because of it.

If you place a 5 mr/hr source next to a 2 mr/hr source, the dose rate meter
will not read 7 mr/hr. Saying a package is <0.2 mr/hr when it is measured
while standing in a 2 mr/hr field is ridiculous.

Charlie Migliore RRPT
mglc98@nspco.com

PS maybe I can use this for my masters thesis <LOL>
   
> -----Original Message-----
> From:	Pollan, Paul B. [SMTP:PBPOLLAN@southernco.com]
> Sent:	Wednesday, October 13, 1999 9:13 AM
> To:	Multiple recipients of list
> Subject:	RE: GM Counters in High Backgrounds
> 
>  Dru, certainly one would think the pulses would be additive, but in
> actuality, the smear in the lowered background reads between 1K and 1.5k
> cpm.  The instrument is calibrated to NBS standards and the CF is fairly
> linear (0.1).  This appears to be an anomaly that the "road" HPs seem to
> see
> everywhere they go when working with fairly high level smears.  When I
> speak
> of high level, I am talking about the 200K-500Kdpm/100cm2 smears (CF
> accounted for) taken usually on the platform and tools by primary Steam
> Generator workers.  I have witnessed such occurrences on a regular basis
> during Outages.  An example is a 200kdpm/100cm2 smear counted in the high
> background actually reads between 180k to 250kdpm/100cm2 on a frisker in a
> 1kdpm background.  I have yet to account for this.  The Eberline folks
> don't
> understand it either.  It's a standing joke in Containment during Outages
> when a person gets a 12kdpm/100cm2 count in a 10kdpm background and calls
> it
> "2k" that the individual is stuck with that name for the whole Outage
> until
> he/she counts the smear in a much lower background and find it reading
> between 12k and 15kdpm/100cm2.
> 
> I appreciate your input - Paul.
> 
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