You probably want 2 instruments: 1) a geiger counter with an end window tube or an ionization chamber for x-ray checking on your system.The X-rays from a working fusor are no joke. Suitable counters can be had fairly cheaply on Ebay. I second all the caveats Richard Hall has mentioned about dealers and the reported condition of goods for sale - be careful. Stay away from the old yellow Victoreen CDV-715 type counters, as they are very insensitive, are optimized for gamma detection, and most of them don't work anyway. Richard Hull reports using a "Cutie Pie" type ionization chamber meter. I have an Eberline RO-3 that is very similar, obtained cheaply through Ebay. 2) The second instrument is your neutron detector. Eberline and Victoreen both make them. I see these pop up several times a year on Ebay. Again, be careful. The instrument you need to use is the one using a moderator around a BF3 proportional counter tube. The moderator slows down the fast neutrons so they can be detected by the counter tube. If you check Richard Hull's fusor site, he has a picture showing one right next to his Fusor III. I have a neutron detector from Tracerlabs ("Snoopy"). It has a cylindrical moderator that makes it look like a big, black bomb. The are also neutron detectors I've seen that use a bare BF3 tube. Stay away from these, as they are no good for detecting the fast neutrons generated by the D-D reaction.
Another option might be to put together a proton recoil detector using a hunk of plastic scintillator and a photomultiplier tube. Check Joe Zambelli's posts on this. If you're willing to settle at first for simple go/no go indication of neutrons, this could work. This will involve some constuction work and some electronics, but the ingredients are on the whole easier to get than a store-bought neutron detector. I intend to try both my "Snoopy" and a proton recoil detector when the time comes....
Created on Thursday, March 29, 2001 1:05 PM EDT by Richard L. Hester