Re: sodium iodide scintillation detectors

[John_Sukosky@DOM.COM]

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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