How about using several photodiodes with each their own amplifiers

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Oh I forgot about Thorium in my lamp mantles! My coleman latern is out in the shop. Better to get a new mantle though, not as fragile.

George H.

Oh I forgot about Thorium in my lamp mantles! My coleman latern is out in the shop. Better to get a new mantle though, not as fragile.

George H.

I've been told by colleagues who do radioactive detection for a living that some modern lantern mantles are doped with cerium rather than thorium and are not radioactive above background. They tell of taking a Geiger counter into the store to find the "good" mantels for their radioactivity is everywhere demonstrations.

Bret Cannon

On a sunny day (Wed, 25 Apr 2012 17:46:05 -0700 (PDT)) it happened George Herold wrote in :

I have some Thorium containing welding rods, much safer than mantles, as they are rock solid, and legal everywhere too. Ebay :-)

Well, a scintillator isn't collimated at all, the photons shoot out from the interaction in all directions. But, a properly made light guide should work like an optical fiber, all hits on the side of the guide should be glancing, and therefor totally reflected back in. The idea is to try to make sure as few photons hit the walls of the guide more normal than Brewster's angle. But, that can be tough. With a thin disc of scintillator, it works better, but with a big block of scintillator you can shoot more photons more directly at the walls of the light guide.

Anyway, for charged particle detection, thin scintillators are all you need, just a couple mm thickness will stop anything that comes out of a source. The huge blocks of scintillator are only needed for detecting Gamma rays, which have much deeper penetration. So, a charged-particle detector can best be built by putting a square slab of scintillator directly in front of a square PD, with a little silicone grease as a coupling material. If the energies are high, you can put white Teflon tape around it, but the downside is the particles have to punch through the Teflon to reach the scintillator.

For a first test, I'd just put the scintillator directly in front of the PD, no light guide and no wrapping or paint.

Jon

Well, one of the interesting things is to test the amp without the detector, then with the detector with no bias and then with reverse bias on the detector. The lowest noise will be with no detector (detector capacitance increases noise gain, and also there is thermal noise generated in the junction.) This is worst with the detector un-biased, you can watch the noise drop dramatically with even a few Volts of reverse bias.

Rf really only controls the time it takes to recover to baseline.

Jon

Right, I think the Thorium ones are not legal for sale anymore, or are at least being phased out.

Jon