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]