Hi Joe...

We have seen a similar buildup at the base of our ion source on our  
Delta Plus XL, though it was due to a different reason.  One of the  
leads of our filaments had broken, and we used a little clamp to  
clamp the broken wire back together.  The screws in this little clamp  
were coated with zinc, which is apparently a bad metal to have under  
vacuum as it degases.  The result was a coating similar to yours.

We solved the problem by using a bead blaster we have in our lab that  
we use to clean filaments for thermal mass specs.  It did a very nice  
job of cleaning off the grime without damaging the metal or ceramics.

Do you know of anyone with a bead blaster?  I would suggest larger  
round beads (~ 100 micron diameter) at low pressures so as not to be  
aggressive.

Hope this helps...

Tim Prokopiuk

On 27-Mar-06, at 3:40 PM, Joe Lambert wrote:

Hi All,

     We have a Delta Plus IRMS that is about 5 years old and recently  
have
started having problems with arcing in the source, which is shutting  
off the
high voltage on the machine.  We belive the problem has to do with a
build-up on the ceramic leads at the base of the source (see attached
picture).  This build-up may be graphite.  A glass-fiber brush seems to
remove the material but the brush is too bulky to reach some of the  
surfaces
in tight places.  Has anyone seen this happen to their source before  
or does
anyone have any ideas on how to clean this?  Acetone and alcohol did not
remove anything.  The ceramic pieces are not removable and if broken  
would
be bad news.  Our last resort is a 5% nitric acid solution, which we are
trying to stay away from if possible.  If the attached image does not go
through, the picture of the dirty ceramics can also be viewed at:

http://www.bama.ua.edu/~lambe012/DirtySource.jpg

The strange thing is that the rest of the source is almost as clean  
as if it
were brand new.

Thanks,

Joe Lambert


W. Joe Lambert
Research Scientist
Alabama Stable Isotope Laboratory
University of Alabama
Geological Sciences
202 Bevill Building
7th Avenue
P.O. Box 870338
Tuscaloosa, AL 35487-0338
Phone: (205) 348-4404
Fax: (205) 348-0818
email: [log in to unmask]
Visit our web-site: http:www.geo.ua.edu/asil


-------------------------------------------------
Tim Prokopiuk
B. Sc. Geology/Technician
Saskatchewan Isotope Laboratory
Room 241
Department of Geological Sciences
University of Saskatchewan
114 Science Place
Saskatoon, Saskatchewan, Canada
S7N 5E2
Phone: (306) 966-5712
Fax: (306) 966-8593
Email: [log in to unmask]