Mark,
   When you heat the analyzer the beams quickly go off path...after you turn 
the anlyzer heater on and the signal drops, redo the peak center and you should 
see the real bgnd
Greg

Quoting Mark Haught <[log in to unmask]>:

> Hi Andrew,
> 
> It seems like the heating is making the source gasket seal tighten and the
> cooling causes it to loosen and produce a slight air leak.
> 
> Mark
> 
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
> Of Andrew Schauer
> Sent: Tuesday, March 10, 2009 12:35 PM
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] MAT253 Heater Background interaction
> 
> Hi all,
> 
> I have observed high backgrounds on our MAT253 for masses 28 and 29 (conflo,
> EA) that drop very quickly upon turning the Analyzer heater on. This is the
> heater that takes hours to heat the entire block of metal up surrounding the
> source. The drop I observe starts seconds after turning the heaters on (NO
> OTHER HEATERS TURN ON). On the outside of the metal block, heat is barely
> detectable by touch. When no heat as been applied for hours and the entire
> flight tube is at room temperature and I heat the same area where these
> heaters are located with a heat gun, I observe the opposite. Backgrounds go
> up. Here is a jpg of the trace I captured today.
> 
> http://depts.washington.edu/isolab/temp/090310_heater_background_drop.jpg
> 
> Vacuum doesn't measurably change. The heaters are located toward the magnet
> and adjacent to the main turbo. If I leave all heaters on over a weekend,
> turn all heaters off and allow the system to return to room temperature, the
> background come back up. Any thoughts? Thanks.
> 
>  Andrew Schauer
> ISOLAB
> Department of Earth and Space Sciences
> University of Washington
> Seattle, WA 98195
> 
> 
> 206.543.6327
> [log in to unmask]
>