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Re: Detectors and humidity



Air density decreases with increased relative humidity.  It's because you

are displacing heavier molecules (O2, N2) with lighter ones (H2O).  Ask any

pilot.



Vincent King

Grand Junction, CO





----- Original Message ----- 

From: <John_Sukosky@DOM.COM>

To: <jjshonka@Shonka.Com>

Cc: <radsafe@list.vanderbilt.edu>

Sent: Tuesday, June 01, 2004 4:47 AM

Subject: RE: Detectors and humidity













Joe,



I'll take you up on your offer of the equation that shows the density of

air is reduced with humidity.  I've had much interest in this, both on and

off the Radsafe list.  It's not intuitively obvious (one would expect air

density to increase with an increase in humidity and therefore less alpha

efficiency at higher humidity).



Thanks,



John M. Sukosky, CHP

Dominion

Surry Power Station

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



----- Forwarded by John Sukosky/NUC/VANCPOWER on 06/01/04 06:39 AM -----



                      "Riely, Brian P."

                      <brian.riely@ngc.        To:

John_Sukosky@DOM.COM

                      com>                     cc:

                                               Subject:  RE: Detectors and

humidity

                      05/28/04 03:00 PM













Hi John



Joe said



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

humidity (I can get you an equation if you like)..."



When Joe gets time, I would like the equation.



Brian



-----Original Message-----

From: John_Sukosky@DOM.COM [mailto:John_Sukosky@DOM.COM]

Sent: Friday, May 28, 2004 1:06 PM

To: radsafe@list.vanderbilt.edu

Subject: Detectors and humidity















----- Forwarded by John Sukosky/NUC/VANCPOWER on 05/28/04 01:05 PM -----



                      "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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