Merry Christmas, everyone. For those not already on holidays:

Running dD on our Delta XL, I first noticed that I had a weird shape 
when peak centering. Mass 2 shows shoulders on either side, with flat 
tops. Mass 3 and all masses on the universal collectors seem fine.

H3 correction came in at an astonishing 0.7 (compared to the usual 
7.0 to 8.0).

Almost as astonishing is that I was able to make measurements. No 
problems with drift, fluctuations, etc. Calibrations and multiple 
standards all checked out. No loss of sensitivity. Good repeatability.

My first thought was the energy filter, but I think that is on the 
mass 3 cup. My second thought was for the electron suppressor, as 
that can give odd peak shapes, but I'm not convinced (I don't think 
it explains the flat tops of the shoulders). No tuning parameters 
seem to have an effect. Mass spec wasn't opened up for cleaning or 
anything. Vacuum also fine.

I can send a peak scan to those interested. The normal peak is 2000 
to 2400 steps HV. There is a flat top shoulder (90% height) from 1800 
to 2000 steps, and another (10% height) from 2400 to 2600 steps. Saw 
a similar shape with a magnet scan over the peak.

Paul Eby


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Biogeochemistry Lab (E-Hut, room 102)
School of Earth and Ocean Science
University of Victoria

PO Box 3055
Victoria, B.C.
Canada
V8W 3P6

phone: 250-721-6183
fax:   250-472-4620