[ RadSafe ] low energy gamma-spikes

[Dixon, John E. (CDC/ONDIEH/NCEH)]

Depending upon the physical configuration of your NaI detector (i. e. does it have a thin window, etc.), I have seen strong signal responses from X-Rays in the 2 - 5 Kev range. A high dose rate is not needed to give a response to 25 Kev X-rays. The vulnerable component here is probably the photomultiplier tube associated with the detector. The PMT is susceptible to EM interference.
 
John E. Dixon

________________________________

From: radsafe-bounces at health.phys.iit.edu on behalf of Alston, Chris
Sent: Tue 9/28/2010 1:51 PM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] low energy gamma-spikes



Marco

Yes, the doserate would have to be very high for an E-compensated GM detector to see something at 25 keV.  Noise from the high tension power lines would be my first guess, too.

Cheers
cja

-----Original Message-----
From: marco bähler [mailto:m.c.baehler at bluewin.ch]
Sent: Monday, September 27, 2010 2:51 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] low energy gamma-spikes

dear group

I live close to an old bwr and went for a walk with my BNC 935 / 3inch NaI. it was towards the end of the annual refueling period.
500m downwind, calm wind, on the open field  suddenly I recorded several short alarms, lasting between one and 12 seconds. countrates up to 15000cps. energy almost exclusively around 25 keV. I am wondering what this could have been.
answers from the authorities range from "noise due to high tension lines" (actually 200m away) to "probably x-ray exams somewhere" and  "no hear no see no say" or "cosmic particle showers".
one answer referred to the gm-tube-equipped doserate-monitoring network which "recorded nothing". I think it is quite common for compensated gm tubes not to see 25 keV.
Is someone of YOU familiar with such spikes (me thinks I can call them clouds) and knows possible sources/causes? (Cd109??)

kind regards and thankyou for pondering

marco bähler
(euratom level 5b, 2004 utrecht)
uetikon
switzerland


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