John,
Yes, by default only one bubbler on the JEOL as normally all the P10 channels are in series. I assume one reason for having separate regulators and bubblers on the Cameca would be that they use different pressures ("low" and "high" pressure counters) for different x-ray energy ranges. On the JEOL all P10 counters are at the same pressure as sealed Xe is used for high x-ray energies.
But I've seen at least one JEOL where the P10 line is split upstream from the spectros to have an individual supply for each P10 counter (and I think also a separate bubbler).
I was curious and did some testing on our 8530F+ where the three P10 spectrometers are currently in series. I moved the last spectro in the line on a major element peak, and then did the same for the first and second spectro while monitoring the count rate on the last spectro in the line. There is no noticeable change even at very high count rates on the first two spectrometers. So "recycling" of the gas further down the line does not appear to be affected by what's happening on spectrometers upstream.
I've also heard that one may see differences in count rates when changing the order of the spectrometer in the P10 gas chain on a JEOL instrument, i.e. the spectrometers further downstream can have lower count rates. But I'd assume that may be due to P10 leakage somewhere in the chain, e.g. a leaky detector window, or a tube not attached properly...?
Dave,
I don't have any experience with these back-pressure regulators. I can see how it might help in your case at high altitude, but do you think it would also make a difference for us, being pretty much at sea level? I.e. in addition to preventing potential backstreaming, could they even out fluctuations in atmospheric pressure? There seem to be a range of designs available. How much of a pressure difference to atmospheric pressure would one have to set for them to operate properly? Obviously too much pressure on the detector windows etc would be a concern.
Cheers,
Karsten