[ RadSafe ] Skyshine measurements

Ted de Castro tdc at xrayted.com
Thu Mar 7 00:09:51 CST 2013

On 3/6/2013 8:58 PM, Victor Anderson wrote:

| Good Evening,

| This is indeed interesting. Perhaps Ted could share some of his results.

Not sure what results you'd like --- or what I may still have after I 

| The trick of using 1 inch (2.54 cm) by 12 inch (30.48 cm) compensated 
GM tubes is intriguing. One big question is how sensitive these 
detectors are.

They are sensitive enough and reliable/stable enough that I could see 
the annual variation in background radiation - I believe due to moisture 
content in the ground.  I could also look at the record and see when 
rain would start - and back ground jump due to washout - when it was 
raining - a decrease in background until the ground was saturated - and 
when the rain was over - an increase in background as the ground dried.  
All this with 10 minute counts.

Typical calibration factors for the two detector types are:

11000   counts/mREM neutron   76647 counts/mR gamma

That one time the ALS was having problems and ran in FILL mode for 2 
weeks straight I was able to find all those 10 minute intervals that 
were totally within beam ON times and those totally without and 
determine site boundary exposure rates from FILL to be  0.6 microREM per 
Neutron and 0.02 microREM per hour Gamma.   Total data collected was a 
couple of 100 hours each for ON and OFF periods.  This I found in some 
notes I saved.  I also calculated the statistical significance for those 
results but couldn't find that report quickly - but if memory serves it 
was significant to something like 15 standard deviations.

Therefore I think these instruments - commercially available - would be 
at least sufficient to determine skyshine variations with weather 

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