Day/Night background change?

[paquette@shaman.nexagen.com (Tom Paquette)]

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