Re: LN loss from Germanium Detectors

["Gary H. Kramer" <gkramer@hpb.hwc.ca>]

Greetings

I should clarify that our Dewars are large, and weigh 26 kg when empty.  
It would be a difficult task to weight them on a regular basis.  They 
first must be dismounted (a two person process) from the suspension 
system in the counting chamber, then transported to a scale, weighed, 
and then remounted (another two person process).  I estimate that this 
would take one of my technologists an hour or more, plus they wouldn't 
like it!

A pizoelectric sensor underneath the detectors once they are mounted would 
be perfect, but too expensive.

Leakage current monitoring is a thought, except that it's really hard to 
get at with this detector design.

In response to a question:  yes, the LN is vented into the counting 
chamber.  I don't know if this will make any difference as the loss rate 
is small.  (yes, we also monitor the oxygen content when subjects are in 
the chamber).  Typical loss of the detector-dewar assembly was 65 gm LN 
per hour when they were first commissioned late last year.

Regards

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| H   H   M       M   L	       Gary H. Kramer  		              |
| H   H   MM     MM   L        Head, Human Monitoring Laboratory      |
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