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Well-type scintillation detectors for spectroscopy

Posted: Wed Nov 04, 2020 8:29 pm
by ChristofferBraestrup
Hello!

I apologize if this has come up before. If it has, I couldn't find it.

I'm looking to upgrade my square Bicron 1.12x1.12M3, which, as many before me have learned, doesn't offer the greatest resolution or sensitivity.

I know there is no way around the fact that larger crystal is better and more expensive but there are quite a few 2" and larger dia. well-type probes on Ebay.

So I would like to hear some first hand experiences with these for gamma spectroscopy - are they worth it at all?

Is side well or end well generally speaking 'better' ? And what is the smallest spectroscopically usable size well counter?

Thank you in advance!

Re: Well-type scintillation detectors for spectroscopy

Posted: Wed Nov 04, 2020 9:09 pm
by Richard Hull
I have an end-well, 5" Bicron crystal and PMT combo with matching preamp. To effectively use any end-well, you must be able to place the sample fully within the well. (physical limits). Just going bigger is not always the answer as I learned to my cost. Well type scintillators are traditionally used where extremely weakly emitting gammas are to be detected. Likewise, the larger sizes are always enclosed in a 1000 lb. lead castle.

Regardless of what source I dropped into my naked 5" well-type, I got a radium signature, (goldie lock and the three bears). This was due to a high background level. Unless you are measuring ultra weak sources and have a well-type enclosed in a giant castle, I would suggest nothing larger than a 3X3 square xtal for amateur gamma spec work. This is what I settled on and has served me brilliantly as a compromise between background levels and usable detectability of moderately low, gamma emitting, source spectroscopy.

Richard Hull

Re: Well-type scintillation detectors for spectroscopy

Posted: Wed Nov 04, 2020 11:32 pm
by ChristofferBraestrup
Thank you for the notes, I was actually under the impression that spectral resolution got worse if the sample was inserted into the well, compared to just outside it, but that counting efficiency was much better. My plan was to primarily use the well detector with an external sample, but of course, having both options are nice.

I've seen some batteries of 4 2" well detectors fairly cheaply, I think they're scrapped from radiomedicine dosing counters.

I live in a fairly low background area (Denmark is like 2 km mud before bedrock), so I suspect persistent radium peaks won't be an issue. As a side note, isn't the radium peaks useful as a "built in" calibration source? A background subtraction spectrum would remove most of them afterwards.

Re: Well-type scintillation detectors for spectroscopy

Posted: Thu Nov 05, 2020 12:49 am
by Richard Hull
Correct! Background subtraction works well, but also subtracts a bit from what you have already captured and want to measure. Not much, but real for very quiet samples.

Richard Hull

Re: Well-type scintillation detectors for spectroscopy

Posted: Thu Nov 05, 2020 10:52 pm
by ChristofferBraestrup
We will soon find out how well they perform compared to the square bicron detector. I just purchased a 4-detector module of what looks to be 2" by 2" side-well detectors, complete with dividers for a bargain (50$!). I shall update this thread once they arrive. There really is no substitute for having multiple duplicate instruments in asessing the condition of them!