by Doug Coulter » Fri Apr 22, 2011 3:35 pm
Absolutely. I don't know what sort of neutron source you've got, but we made a couple with staticmaster sources and Be and they can barely get my most sensitive 3He out of the noise at all, and then you're not really sure. Compared to a fusor, those tend to be pretty weak tea (10's of neutrons/second) -- or impossible for normal people to get. The old guys were using ~ a curie of alpha emitter! You'll not find one of those, and you wouldn't want to be around it if you did. Carl's little source that went clickety click on a 2 foot 3he tube was hundreds of smoke detectors worth of alpha source. Industrial ones.
I'm not sure what they're saying about coronal discharge there, no standard detector books I've got mention such a thing for any sort of detector. They seemed to be saying 25 uA leakage max or something like. I also notice he's got a little confusion between slow neutrons and gamma in one of his titles. I mean, it's a tube with gas in it -- there's not a lot of fancy tech involved. Usually these have to run with real high impedance (megs) or they do go into glow discharge and won't count any more (and are ruined). Each count creates a discharge, you measure that, but there has to be low enough DC current available so it can "turn back off" after that else they are just lighting up in there and "turned on".
At any rate, at first I thought having a neutron source would help me calibrate things like this for the fusor, but it worked out the other way around -- now that I know things work in a real loud neutron flux, I can start working closer to the noise on a "passive" neutron source. Tens of neutrons/second won't get most detectors out of background so's you'd notice. If you are getting some per minute of cosmics, the actual quantum efficiency of these is such that 10's per second entering the moderator won't make enough hits to get reliably above the background the QE of these is pretty low as a system. First, most of the neutrons scatter out of the moderator, then only a few of those that get into the tube count it.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.