Andrew

Mark is probably correct as we had a similar problem a while back. 
However, it wasn't the source flange but the seal in the variable 
conductance valve on the top. We found the leak using a syringe with 
acetone and tuned to mass 43. We always use a torque wrench to tighten 
the flanges.

John
UCL.

Andrew Schauer wrote:
> 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]
> 
> 
>