Hmm. I played with every tuning parameter available to me, including 
the electron energy, by making wild adjustments (not small tweaks). 
No changes to the EE or any other parameter made a difference....


At 08:31 AM 22/12/2005, you wrote:
>The awkward mass 2 peak arises from He++ ions which can become 
>prominent when the electron beam energy is set to values of 90V or 
>larger. The mass separation of the Delta machines is not large but 
>large enough to show a composed peak. Remedy: Adjust the electron 
>energy to around 70 eV. This will suppress the H2++ to less than 200 
>mV (I think).
>Regards    Willi
>
>Paul Eby wrote:
>
>>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
>>
>>
>>[log in to unmask]
>>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
>
>--
>.....................................................................
>
>Willi A. Brand, Stable Isotope Laboratory      [log in to unmask]
>
>Max-Planck-Institute for Biogeochemistry
>
>Beutenberg Campus
>Hans-Knoell-Str. 10, 07745 Jena, Germany      Tel: +49-3641-576400
>P.O.Box 100164,      07701 Jena, Germany      Fax: +49-3641-577400
>
>         http://www.bgc-jena.mpg.de/
>         http://www.bgc-jena.mpg.de/service/iso_gas_lab/
>
>GASIR 2005 in Jena:
>http://www.bgc-jena.mpg.de/service/iso_gas_lab/gasir2005/index.shtml
>
>
>.....................................................................