I paid about $150 for my Tracerlabs "Snoopy" neutron detector in an Ebay auction, non-working of course. Richard Hall reported paying around $50 for his latest acquisition. Obviously, your milage will vary. Don't count on anything of this nature that you get from Ebay to work right out of the box, unless the seller offers some sort of guarantee (rare). Photomultipliers can be had fairly cheaply - there are a slew of them for auction on E-bay right this moment.Other surplus sources on the Web regularly offer them for sale as well. I would get something in the range of 1.5" diameter to 3", with a bialkali photocathode. You will need a base, a high voltage supply (somewhere around 600 -1000V and quiet), a preamp, and a case with magnetic and light shielding capability. Some radiation shielding might also be necessary to bring down the background noise. Mc Master-Carr offers the nickel-iron magnetic shielding material. You might be able to omit the magnetic shielding if your environment is fairly benign, but light shielding is a must, as well as electrical shielding. I'd count on having a metal case. A basic 3-transistor preamp circuit is archived on one of the sites linked to this one - it looks like a good starting point, and uses readily available transistors (2N3904 and 2N3906). Check the Bicron web site for information on choice of resistor and capacitor values for the dynode string you will need hanging off the tube base. They also have a lot of basic information on scintillator and PMT technology in PDF format. The Hamamatsu site is also a good one to check. If you can get a pin base with adynode string included, so much the better. You may also need some sort of pulse-height discriminator to strain out low level garbage. This could be as simple as a comparator, a quiet voltage reference, and a ten-turn potentiometer to set the discrimination level. You will probably want to check with Joe Zambelli on this, as he actually has a PMT/Scintillator setup up and running. I could not tell you at this point what the difference would be in the pulse count with or without a discriminator. Picking up an SCA (single channel analyzer) would not be a bad idea. The plastic scintillator can be had from Don Orie at OE Technologies (oetech.com. He has prices listed on his web site. I am deliberately coy on the pricing of the above setup, because a lot of the pricing will come down to luck and how good you are with electronics and Jimmy-rig fabrication, as well as how much junk you already have laying around.
Created on Monday, April 02, 2001 1:12 PM EDT by Richard L. Hester