re: High Dose/Landauer

[JDT4%RP%DCPP@bangate.pge.com]

Radsafers,

As I see it, there are three possibilities for the high exposures noted, two 
of which have been discussed at some length on this recently:

	1)  The dosimeter processor could have mis-read the badges.
	2)  The badges could have been exposed during shipment.
	3)  The doses might have been real.

As regards item 2, we have experienced it on one occasion that we know of.  We 
process our own dosimeters (conveniently eliminating item 1 as a possibility) 
but must send dosimeters out on occasion for inter-comparisons, NVLAP 
performance testing and the like.  

On one of our shipments we found a significant transit dose.  Historically, we 
see background values of around 10-20 mR for shipments such as these.  The 
controls included with this shipment indicated as much as 300 mR signal and as 
little as about 80 mR, which means that the geometry of the exposure probably 
included a large gradient.  Most likely, there was a point source located 
adjacent to our shipping container at some point during it's travels.  The 
badges were not arranged in any particular order in the container so there was 
no way for us to determine how much transit dose any one particular test badge 
might have received.  We were unable to positively identify the source of the 
exposure.  

It is conceivable, though not very likely, that the exposure occurred on the 
loading docks of the testing laboratory where it sat over a weekend, or in our 
own warehouse.  Most likely, it occurred while Federal Express had custody of 
the shipment.  Unfortunately for us, this particular shipment was one of our 
NVLAP performance test groups.  The incident caused us a great deal of grief 
and jeopardized our laboratory certification.  

The point of relating this experience is that, while we could not pinpoint the 
cause, we _did_ find out that neither Federal Express nor UPS would guarantee 
segregation of our dosimeters from radioactive materials shipments.  Airborne 
Express, on the other hand, said they would.  We switched to them and haven't 
had a problem since.  Of course, we might not have had another problem with 
the other guys either, but why risk it?

Jack D. Topper
Dosimetrist
PG&E Diablo Canyon
jdt4@pge.com

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