Photo-Multiplier tube voltages?

Question

At the lab, there is a smoke chamber and it has a photo tube.

This is this problem, for what ever reason the lab has 0 documentation of the electronics and the service tech they tend to use for calibration does not know any more.. All he knows is what it suppose to be at the end of the anode with a 1MEg load on it, which is 0..5V ..

Ok, all that is just fine however, there is some confusion about the voltage requirements for this tube, of course, we can't find any spec's on that either.

In any case, after looking at generic photo multiplier tubes and circuits it appears that -600DC at the cathode seems to allow this to work ok when we calibrate for dark current. We need the tube to have some linkage at dark current so when the filter is applied we have a detectable view of the smoke.

Does 600V sound about right?

The calibration tech seems to think it should be down around -350VDC which works fine for a clear view but has a drop off so the filter view has very low sensitivity, which makes perfect sense to me since the tube needs to be ionized to get some leakage.

We do have photo multipliers in use elsewhere however, those supplies are up around 1kVDC and that we do have proper specs and design work but they are a much larger tube, the supply in the smoke chamber unit can only output up to -700DC.

What's your take on this voltage scale?

Jamie

Jan Panteltje · Accepted Answer

On a sunny day (Sat, 26 Jan 2013 15:51:48 -0500) it happened Jamie  wrote in : What is the tube number, type it in google?

Phil Hobbs · Answer

-600 to -1000 volts is about right.  Normally you get a gain of roughly  3 to 5 per dynode, so that a 7-stage PMT gets you a gain of ~10k and a  12-stage one can go way over a million.  Gains much higher than 10**7  aren't useful, since the typical width of the impulse response is about  20 ns, so with 10**7 gain and a 50 ohm load, a single primary  photoelectron will give you a pulse of 1.6E-19*1E7*50/20e-9 = 4 mV,  which is way above the background, so there's no point in sacrificing  tube life to get more gain. Cheers Phil Hobbs --  Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net

Robert Baer · Answer

From Wikipedia, "Photomultiplier tubes typically utilize 1000 to 2000 volts to accelerate electrons within the chain of dynodes." And i can attest to that, as the manager for Oil 4 Less LLC, we sell high voltage shunt regulators designed for PMTs in downhole applications. The only time we sell 400V regulators is in conjunction with 1250V regulators, giving 1650V for the PMT and a voltage tap for one of the dynodes. Use the Baby Bird (Goo Gull) and look up Hammamatsu PMT specs.

Jan Panteltje · Answer

On a sunny day (Sat, 26 Jan 2013 13:54:11 -0800) it happened Robert Baer wrote in :

No way without looking it up. I have some Russian PMTs here that start at 350V, PMT_FEU-35. Type number should be on the internet really.

Jamie · Answer

Thanks Phil, that just about covers it then.

We do use 12 stage units at a -1KDC for the detection of the slightest arc that could take place inside a vessel that gives us the voltage for the 2Mev ebeam.

As for the tube number in question for the other poster, I don't have it at the moment. Memory tells me it was something like 7102 or something, but it's a side view detector with 11 pin octal base with all pins occupied. That could mean 9 dynodes with cathode and anode, maybe..

Jamie

MrTallyman · Answer

Bwuahahahahahah!

some PMTs those must be.

Ours, which power the PMTs still in use in the F-4 Phantoms in Japan and Israel, were of the 1650V variety, and that went through the whole string on the dynode array.

The big key is keeping the leakage current to less than 3 picoamps.

The tube socket is the most common culprit, and almost certainly why their lame design does not carry ay higher excitation voltage.

Ours can see a single photon. Like the launch flash of a missile fired

15 miles behind the plane.

Robert Baer · Answer

* Lazy...

Robert Baer · Answer

Please refer to:     The PMTs.pdf copy is a good reference, as well as the  PMT_handbook_v3aE.pdf which is by Hammamatsu.    Both were downloaded from the web.

Photo-Multiplier tube voltages?

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