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Re: Day/Night background change?
One possibility is that these night time alarms are due to diurnal variations
in radon daughter concentrations near the ground. See NCRP 50, "Environmental
Radiation Measurements", pp. 19ff: "Significant diurnal and seasonal
variations of Rn-222 concentrations are observed and can be mostly explained
by changes in atmospheric stability conditions...both radon nuclides [thoron
and radon] tend to exhibit maximum ground-level concentrations in the early
morning hours when the most stable conditions tend to occur." You said that
the alarms are caused by Security personnel, who were probably walking around
outdoors before entering the building. If you have detailed, local
meteorological data, you could check to see if these alarms can be correlated
with recent early morning temperature inversons.
The opinions expressed are stricly mine.
Here's to a risk free world, and other fantasies.
Bill Lipton
liptonw@detroitedison.com
Radsafers,
We have GM foot monitors at our restricted space exits set to
alarm at about 3 times normal background. There has been little in
the way of spontaneous alarm events in the last year, except the last
two months when security guards are encountering nighttime alarm-trips
when no occupational workers are in the building. This suggests
the possibility of a nighttime background change which would increase
the probability of a spontaneous alarm trip. Is there a day/night
difference in background radiation?
I'm sure you can suggest other reasons why the observation of
the alarm tripping could be being misinterpreted by me. I'm not sure
why I don't have more spontaneous trips with the alarm set at 3 times
background. This must have to do with the time constant setting on the
Ludlum 177 (slow in our case) and the "run length" of background
radiation events. I'm checking unattended operations in the vicinity
of the monitor in question. For now we'll just set the alarm level up
another background increment.
Thanks. Tom.
--
Tom Paquette, PhD
Senior Scientist, RSO
NeXstar Pharmaceuticals
2860 Wilderness Place
Boulder, C0 80301
paquette@shaman.neXstar.com
biinsite@ix.netcom.com
303-546-7626
Fax 303-444-0672