Re: Day/Night background change?

[rkathren@tricity.wsu.edu (Ron L. Kathren)]

This well known phenomenon has been described in numerous publications.  A
paper in Health Physics by Wollenburg and Smith about 40 years ago documents
such variantions in the SF Bay area.  And, you could alsp check my
admittedly aging book Radioactivity in the Environment which treats the
subject of diurnal variations in cosmic ray intensity as well as radon levels.

Ron Kathren

>At 11:52 AM 6/9/97 -0500, you wrote:
>>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.
>You are most likely experiencing fluctuations in the background
>due to radon-thoron increases.  Radon daughter products  will
>have a higher concentration during atmospheric inversions which
>occur most frequently during the late night and early morning
>(pre-dawn) hours.  You are in an area that has somewhat elevated
>radon levels anyway, so this could be more dramatic for you.  I have
>seen similar problems in locations in both Colorado and Arizona
>that are more dramatic during the spring and late winter months.
>
>A good way to check this out is to run a filter type air sampler
>that has a GM detector for live time monitoring and a strip chart
>and see if you are getting upward trends in short-lived activity
>on the air sample strip charts at about the same time that the
>background on your friskers increase.
>
>Best regards
>
>Judd M. Sills, CHP           |   Office: (619)455-2049
>General Atomics, Room 01-166C|      Fax: (619)455-3181
>3550 General Atomics Court   |   E-Mail:  sillsj@gat.com
>San Diego, CA  92121         |
>
>