Re: Detectors and humidity

[John_Sukosky@DOM.COM]

Joe,



Thanks for adding to the discussion.  I'm posting this to Radsafe so

everyone can benefit.  One clarification to your statement:  "...increased

alpha background as a function of humidity..".  We did not observe

increased alpha background as a function of humidity (alpha background was

flat along the entire period).  What we saw was increased alpha source

check count rate that was proportional to the increase in humidity (same

slope).



In answer to your questions, the power is normal feed (no outages with

offsite power).  We have not looked at the beta cams but I will give this a

try.  We do weekly environmental background measurements with our NaI

standup whole body counter and typically see the natural radon products you

describe.  This would probably be easier for us to look at and trend for

naturals.



One additional piece of info about the HPGe detectors.  After reviewing the

data, the humidity to high count rate correlation only appears to take

place when the liquid nitrogen gets low.  After we thermocycle the

detectors, we don't see the correlation.



I'll let you know what we finally figure out.



Thanks again to everyone for taking time out to share your ideas and

suggestions.



John M. Sukosky, CHP

Dominion

Surry Power Station

(757)-365-2594 (Tieline: 8-798-2594)







                                                                                                                                       

                      "Joseph J.                                                                                                       

                      Shonka"                  To:       <John_Sukosky@DOM.COM>                                                        

                      <jjshonka@shonka.        cc:       <JPreisig@AOL.COM>                                                            

                      com>                     Subject:  Detectors and humidity                                                        

                                                                                                                                       

                      05/28/04 10:39 AM                                                                                                

                                                                                                                                       

                                                                                                                                       









Dear John (and Joe):



I am not allowed to look at RADSAFE, since I would waste a good fraction of

the day, but someone forwarded your exchange to me.  First things first,

Joe I hope you were talking about someone else J.



John



I don’t think the supply voltage is the issue.  Although 3 systems are

correlated with humidity, I think that you could be dealing with more than

one cause with the causes correlated seasonally not the supply voltage.

However, if you are talking about outages with offsite power I may

reconsider voltage.



As for correlated causes, for example, the density of air is reduced with

humidity (I can get you an equation if you like), and that may explain the

increased alpha background as a function of humidity, especially for low

energy alpha.  As for the gamma sensitive detectors, Joe Preisig is

correct.  If you “in situ gamma spec” one point on earth every day, you

find the equivalent uranium (from Bi-214) is higher in the wet season

because the small fraction of total radon in soil that emanates to air

increases in wet soil.  Have you looked at any beta CAMs (that do not have

radon subtraction)?  You would need to look at the same time of day (avoid

mid morning, perhaps midafternoon) and look at a few months of winter

versus summer.  The radon you measure comes from a location a day or two

“upwind” of you, which may have greater seasonal variation than your

location.



I am not a member of RADSAFE, but you are free to post my hypothesis if you

like.



Regards and good luck,



Joe Shonka



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