Re: MODEL 44-116 light leak

[DSnowder@aol.com]

Andy, 

Having managed an instrument calibration laboratory for 7 years I can offer
some tips that might help.  

Assuming that the problem is the mylar and not HV settings, PMT damage,  etc.
try the following:

1.  If not already doing it, use double sticky back foam tape around edges of
mylar and seal cover plate up against it. The foam tape acts like a gasket and
seals off any  grooves or damage in the cover or base plates of the detector. 

2.  Check the thickness of the mylar you are replacing to make sure it is the
same as original. If it is thinner than original, you may be getting light
leakage.  If you don't have documentation or know the thickness of mylar you
are using you can confirm by putting second layer of mylar over first layer to
see if leakage is eliminated/reduced

3. Check the mylar you are using for small (almost microscopic) light leaks.
This can be done using a strong bright light. Mylar has a tendancy to
deteriorate after a year or two and develop seperations in its aluminized
coating, especially under certain environmental conditions.  Replace with new
mylar if necessary.          

If none of the above work, problem is probably with something else (i.e. HV
settings, PMT, bad cord, etc.) 

Dale Snowder
VP Alpha-Idaho LLC
(208) 523-5557 
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