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RE: Puzzler: How Does Humidity Affect Counting Efficiency?
Err ... I think you have it backward. Dry air has less conductivity, not more. That's why the static charges can build up in the first place. Moist air bleeds off the charge.
Dave Neil
-----Original Message-----
From: John_Sukosky@DOM.COM [mailto:John_Sukosky@DOM.COM]
Sent: Wednesday, May 26, 2004 12:43 PM
To: Flanigan, Floyd
Cc: radsafe@list.vanderbilt.edu
Subject: RE: Puzzler: How Does Humidity Affect Counting Efficiency?
Floyd,
Thanks. Yes, we considered air conductivity but it would appear to have
the opposite effect. In other words, dry air would have more conductivity
(including more static discharges) compared to more humid air. Humid air
would therefore show a decrease in count rate (not an increase like we're
measuring).
John
"Flanigan, Floyd"
<Floyd.Flanigan@nmcco. To: <John_Sukosky@DOM.COM>,
com> cc:
Sent by: Subject: RE: Puzzler: How Does Humidity Affect Counting Efficiency?
owner-radsafe@list.Van
derbilt.Edu
05/26/04 11:30 AM
Please respond to
"Flanigan, Floyd"
I think there is something to think about. If the humidity effects alpha
but not beta count rate on the Tenelec I tend to lean away from a common
component culprit. Have you looked at a correlation on air conductivity and
electrical component proximity? Just a thought.
Floyd W. Flanigan B.S.Nuc.H.P.
-----Original Message-----
From: owner-radsafe@list.vanderbilt.edu
[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of
John_Sukosky@DOM.COM
Sent: Wednesday, May 26, 2004 8:31 AM
To: radsafe@list.vanderbilt.edu
Subject: Puzzler: How Does Humidity Affect Counting Efficiency?
We've had problems controlling the environmental conditions in our Counting
Lab due to a degradation of the room's environmental control system.
Counting equipment calibration and setting of statistical ranges occurred
during the winter months. As the temperature changed and humidity
increased in the past few months, here in Virginia, our source checks on
some instruments have gone into the warning (> 2 Sigma) and Control (> 3
Sigma) levels. We analyzed the data with temperature, humidity and
barometric pressure. There is no correlation with temperature or
barometric pressure but almost a perfect correlation with humidity. When
humidity goes up, count rate goes up at the same rate. When humidity goes
down, count rate goes down at the same rate. Here's a list of affected
instruments and source check results:
Instrument Type Humidity/Count Rate
Tri-Carb Liquid Scintallation Counter Strong Correlation
Tennelec Gas Flow Proportional Counter Alpha - Strong Correlation
Beta - No Correlation
HPGe High Purity Germanium Strong Correlation
Does anyone have any ideas on what the mechanism could be for this effect?
We suspect that there is some common electronic component between all three
of these instruments that's affected by humidity. What we can't understand
is why the Tennelec Alpha channel is strongly affected by humidity but the
beta channel shows absolutely no correlation with humidity??? It's using
the same source (Pb-210) that's counted at the same time for checking both
alpha and beta channels.
Thanks for any ideas on this. We're really perplexed on this one!
John M. Sukosky, CHP
Dominion
Surry Power Station
(757)-365-2594 (Tieline: 8-798-2594)
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