Is a PMT a PMT ?

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Finn Hammer
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Is a PMT a PMT ?

Post by Finn Hammer »

I couldn't help it, my fingers automatically pressed "Buy it Now", so soon I will have a nice crystal clear 63mm x 63mm NaI-Tl scintillator crystal.

This is the one my fingers bought.
This is the one my fingers bought.

This means that I will need a PMT, but will any 3" Hamamatsu cut it or is there some special variety that would be better than some other.
A friend of mine wants to sell me a PMT from a laser scanner, it is a Burle s83021:

Photomultiplier tube from laser scanner
Photomultiplier tube from laser scanner

And there is a suitable PSU with it.

A suitable psu.
A suitable psu.

Would the Burle be any good?

I know I should sit and wait, or rather study, untill I can answer these questions myself, and R.L. Heath “Scintillation Spectroscopy Gamma Ray Spectrum Catalog” is open on my desktop, but it is a long read.
Forgive me, I am way ahead of myself here, but a guy has to start where he is.

Cheers, Finn Hammer
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Mark Rowley
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Re: Is a PMT a PMT ?

Post by Mark Rowley »

Hi Finn
I bought one of those crystals a couple years back. I used a Hamamatsu R6233 which provided decent resolution for gamma spec. 900v resulted in an average background of around 11kcpm (it’s a whopping big crystal!). Placing it in the lead castle dropped things down to a few cps. It’s been awhile since I fiddled with it but I think my details are recorded on one of the FB groups.

Perhaps by comparing the 6233 specs with the ones you are looking at may provide some answers.

Mark Rowley
ChristofferBraestrup
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Re: Is a PMT a PMT ?

Post by ChristofferBraestrup »

This looks like a buck standard bialkali pmt. I suspect it will do just fine. As long as the spectral response isnt wierd.

Scintillation counting is a very forgiving setup, pmt wise.

The only admitted light is the scintillation light (if you light proof properly!), and they're operated at positive high voltage, which removes a slew of issues like needing to have conductive coating on the pmt at HV.


Good luck!
Rex Allers
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Re: Is a PMT a PMT ?

Post by Rex Allers »

I'm not familiar with that PMT but it would probably be fine as long as it hasn't been abused.

Here's a link to a Hamamatsu PMT guide that is filled with all kinds of great info.
https://psec.uchicago.edu/links/pmt_han ... mplete.pdf

Chapter 5 will probably give you lots of info on circuit options. You definitely need a voltage divider, usually just a string of resistors, to split the voltages between cathode, anode, and all the dynodes.

The power supply looks nice but it appears to be Negative HV (+ grounded). That can be made to work and has some advantages on the signal end, but most scintillator set-ups use a pos HV supply. One sentence from that handbook...

5.1.2 Anode grounding and cathode grounding
"In scintillation counting, however, because the grounded scintillator is usually coupled directly to the faceplate of a photomultiplier tube, the cathode is grounded with a high positive voltage applied to the anode..."
Rex Allers
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Rich Feldman
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Re: Is a PMT a PMT ?

Post by Rich Feldman »

Yay for Hamamatsu guide to PMT's.
Years ago I decided to scrounge no more PMT's before actually biasing at least one from my collection.

One difference between PMT's, aside from window size & orientation, and photocathode material,
is sensitivity to magnetic fields.
All models are wrong; some models are useful. -- George Box
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Finn Hammer
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Re: Is a PMT a PMT ?

Post by Finn Hammer »

All,

Thanks for your patient replies. I have read a lot, and skimmed some, up to page 140 in the Hamamatsu handbook of PMT's, it is an excellent read, and I now know much more about polarity, voltage dividing dynode bias networks (active, passive, decoupled and even C-W ladder), sensitivity, resolution and detection of the output signals.

Fascinating stuff. I realise I should just have read this instead of asking here.

Cheers, Finn Hammer
ChristofferBraestrup
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Re: Is a PMT a PMT ?

Post by ChristofferBraestrup »

You're in for the slightly soul crushing experience of making a really beautiful looking instrument and then completely destroying its aesthetics by flooding it with black tape!

I've just been there!
20210413_010331.jpg
20210413_010313.jpg
20210413_010235.jpg
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Finn Hammer
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Re: Is a PMT a PMT ?

Post by Finn Hammer »

Christoffer,

Is that mu-metal i see there as the last layer? If so, please point me in the right direction to make a purchase.
But with regard to the mess of electrical tape, I think not. I plan to weld up a proper plastic shield from black PVC tubing, and sheet.

Cheers, Finn Hammer
ChristofferBraestrup
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Re: Is a PMT a PMT ?

Post by ChristofferBraestrup »

Mu-metal is not yet installed, this is a bare tube.

All mu metal I've ever owned has been pillaged from scrapped CRT's. But Ebay probably has all you need.
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