PMT Wiring

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Tyler Christensen
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PMT Wiring

Post by Tyler Christensen » Wed Sep 02, 2009 12:55 am

I'm almost done building a scintillator for neutrons and got a power supply for it today on ebay for 800-1100 volts that was claimed to be positive, but it is in fact a negative supply. Picture 1 is the wiring I was going to use but can't anymore. I don't see why I can't use picture 3's wiring (and also eliminate the coupling capacitor). Will this work fine with the same amplifier? I'm not sure if the amplifier I built is current-to-voltage
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Q
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Re: PMT Wiring

Post by Q » Thu Sep 03, 2009 2:34 am

tyler,
it wasnt long ago that i made my own scintilator... i found that the polarity of the power supply doesnt really matter- as long as you apply the volotage to the tube in the correct direction. i have seen pmt's driven with the high voltage on either the anode or cathode side... it just takes a bit of creativity to do it.

the richards (both hull and hester) have provided many postings and schematics on the topic. in fact the second schematic you posted looks vaguely familiar...

anyway, i will dig up my research and see if i can find anything that might be of use to you. the hamamatsu pmt handbook (http://sales.hamamatsu.com/assets/appli ... mplete.pdf) is a must read for this sort fo thing. that said, i'll also say that while its tempting to build the power supply and detector/scaler segments of the scintilator, it is in reality a whole lot easier to save up and buy a good used one. i've done both, and were i to do it again, i'd just go for the used ludlum 2350. (one of my favorite pieces of equipment)

Q

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Richard Hull
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Re: PMT Wiring

Post by Richard Hull » Thu Sep 03, 2009 2:12 pm

Both drawings were mine and very old indeed! The first was hand drawn from looking at a PMT socket assicated with the real Hamamatsu PMT socket and the second was a drafted version of its attached pre-amp. Richard Hester improved on it a bit and posted that diagram. All very long ago. (10 years!) The fusor site was just born then.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Richard Hester
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Re: PMT Wiring

Post by Richard Hester » Thu Sep 03, 2009 6:19 pm

The old Hamamatsu circuit is basically a fast pulse amplifier. A charge sensitive amplifier makes pulse height discrimination much easier, especially for fast scintillators like plastics, as it stretches the input pulse to one with a preset decay time constant and a height proportional to the charge in the input pulse. The circuit need not be much more complicated than the Hamamatsu circuit.
These are several examples shown in the Files section at this site. A Google search for "charge sensitive amplifier" will no doubt also be fruitful.

Tyler Christensen
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Re: PMT Wiring

Post by Tyler Christensen » Fri Sep 04, 2009 5:37 pm

Right now I'm building an LM339 signal inverter which will come after the pre-amp and feed an LM311 voltage comparator to act as a discriminator into a digital pulse counter.

Richard Hester
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Re: PMT Wiring

Post by Richard Hester » Sat Sep 05, 2009 1:33 am

LM339? That's a comparator, not an amplifier. Its opamp companion, the LM324, is way to slow and crippled for use in this application. I have a good discriminator circuit in files.

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