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Re: sodium iodide scintillation detectors
There is no excuse for a crystal failure due to the glue. Though more
expensive, we use special ruggedized hermetically sealed crystals, usually
in stainless steel, in well logging sondes. I have some of these built in
the 1970's still working perfectly. If I were you, I would talk to other
manufacturers than just St. Gobain (they own what was Harshaw / Bicron /
Solon). There is an outfit in that same area called Rexell that is more
responsive, and usually a bit cheaper. Also try Gintek in South Carolina,
and a new outfit down near Huntsville (the name slips my mind).
Syd H. Levine
AnaLog Services, Inc.
Phone: 270-276-5671
Telefax: 270-276-5588
E-mail: analog@logwell.com
URL: www.logwell.com
----- Original Message -----
From: <John_Sukosky@DOM.COM>
To: "Dave Oshlo" <doshlo@mgpi.com>
Cc: <radsafe@list.vanderbilt.edu>
Sent: Friday, August 06, 2004 6:58 AM
Subject: Re: sodium iodide scintillation detectors
>
>
>
>
> Dave,
>
> Based on our experience with two 4 x 4 x 16 inch NaI detectors used in our
> standup whole body counter, the life expectancy is about 12 years. The
> limiting factor is not the crystals themselves but the glue used to seal
> the detector housing the NaI crystal. The glue starts to degrade after
> about ten years allowing humidity to invade the crystal. When the glue is
> degrading and conditions are humid (e.g., summertime in Virginia), the NaI
> crystal absorbs water and you'll see a significant decrease in detector
> efficiency. When conditions are dry (e.g. wintertime), the NaI crystal
> will start to dry out and you'll see a corresponding increase in detector
> efficiency. The good news is that you can send your NaI detectors back to
> the manufacturer (e.g., St. Grobain) and they dry out the crystal and
> reseal it into another detector housing. By doing this you can
> indefinitely extend the life of your NaI detector. The drying out and
> resealing process takes about a month for the large 4 x 4 x 16 NaI
> detectors.
>
> I'm not sure what the shelf life of NaI detectors are in a warehouse.
> However, it's likely to also be dependent on the glue that's used as a
> sealant. Check with a crystal manufacturer such as St. Grobain to get a
> definitive answer to this. Hopefully, the glue they're using today is
> better than what they used 20 years ago.
>
> John M. Sukosky, CHP
> Dominion
> Surry Power Station
> (757)-365-2594 (Tieline: 8-798-2594)
>
>
>
>
> "Dave Oshlo"
> <doshlo@mgpi.com> To:
<radsafe@list.Vanderbilt.Edu>
> Sent by: cc:
> owner-radsafe@list.Van Subject: sodium
iodide scintillation detectors
> derbilt.Edu
>
>
> 08/05/2004 02:46 PM
> Please respond to
> "Dave Oshlo"
>
>
>
>
>
>
> Dear radsafers,
>
>
> I’m looking for two pieces of data on a typical sodium iodide
scintillation
> detector but can find inadequate documentation.
>
>
> 1. What is the life expectancy of a sodium iodide scintillation
> detector in an operational nuclear power plant environment?
>
>
> 2. What is the shelf life of a sodium iodide scintillation detector
> (in the warehouse as a spare part)?
>
>
> An exhaustive web search has not provided any solutions. If someone could
> point me in the right direction, I would be much obliged.
>
>
> Thanks,
>
>
> Dave Oshlo
>
>
> MGP Instruments
>
>
>
>
>
>
>
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