Author Topic: Flow proportional counter problems  (Read 111 times)

Mike Spilde

  • Post Doc
  • ***
  • Posts: 18
Flow proportional counter problems
« on: June 16, 2022, 09:42:20 AM »
I have 3 spectrometers with flow proportional counters On my old JEOL 8200. The window burst on the middle detector, so I isolated it and bypassed it with the P10 gas line while waiting for a new window. I now find that the gas outlet detector (Spec 5) provides a high count rate on the peak when the sample is first exposed to the beam, but the counts rapidly fall off by about 90% and then levels off. If I blank the beam for a few minutes and then unblank, the behavior is the same, high counts that rapidly fall off to about 10%. Spectrometer 1, with the gas inlet, was exhibiting the same effect but to a lesser degree, suggesting that something was up with the gas. I’ve seen recommendations that the gas cylinder be rolled around to stir the gas so I tried that, waiting overnight for any debris in the tank settle before hooking the regulator up again. It actually seemed to help, at least for the inlet spectrometer but not much for the outlet spectrometer. It also seems to be dose dependent: at 1nA they both are steady, but at 10nA, Spec 1 drops slightly but 5 falls off by 90%, and at 20nA, both drop in count rate after a few seconds.  I haven’t seen this before kind of behavior before, so I wonder if dust or moisture could have been pulled in when the window burst? I’ll attach some chart recordings. The green trace is Spec 1 and the pink is Spec5. Anybody got any ideas?