Dear Marcin, thank you so much for your very thorough reply! I will surely try and find out about this process 7508. As for point #2, It seems very plausible that that could cause problems for the system. However, I have already tried disabling all visualization but I always get the same errors. =( I will try and find some unix expert that can come have a look at my errors and maybe tell me the origin. For point #3, I have only simulated back to back 511keV photons as a first simple case. I figured I'd get that to work, then go via the positrons... And unfortunately I only have the one computer I'm working on. I will look into the geometry test errors as well (my other post "geomTest Error: overlapping daughters and overshooting daughter volume"), and see if that is connected somehow. Either way, if I manage so solve the problem I will post the solution! Thank you very much again, I really appreciate your help! sincerely, Ida <div class="gmail_quote">2009/9/24 Marcin Balcerzyk <<a href="mailto:m.balcerzyk@pluri.ucm.es">m.balcerzyk@pluri.ucm.es</a>> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div link="blue" vlink="purple" lang="EN-US"> <div> Dear Ida. I am no expert in debugging Gate, but I have three suggestions: 1. Double check what is the process 7508 doing (number in your description of the problem from 23 Sept.). If this is Gate itself, there is no clue, but if any other program – it may be indicative. 2. Disconnect visualization of gamma tracks. I have seen it once in early days of my Gate simulations, that graphic subsystem simply chokes at high rate or amount of the events or when there is simply too many. If you use 10Bq it does not seem as high activity at all, but… As the problem appears only at longer times of simulation, it is rather not the Gate macro itself. Note first sensible (to me) message of stacking the trace in your debugging message: #5 0x011aaa56 in TUnixSystem::StackTrace. All else seems like very deep Unix system error, distantly related to Gate. 3. For the same reason of speed, as in point 2: if you have a choice, try to run the same macro on a significantly slower system. I experienced segmentation violations when positrons did not annihilate on the way from the source and did not find any material to react with and escaped. On a slow system a few escapes during few tens of minutes of simulation were not a problem, Gate could handle this, but on a same Gate version with the same macro on a system with 4x the speed, the escaping positrons induced rapid segmentation violation. If anything of that works, let me know. I am just curious. Best regards Marcin Balcerzyk Instituto Pluridisciplinar Universidad Compultense de Madrid Paseo Juan XXIII n. 1 28040 Madrid, Spain tel. +34 91 3943261 fax. +34 91 3943266 movil +34 697 322 126 Skype: balcerzm </div> </div> </blockquote></div>