Building a detector with a Scionix Scintillator

[Paul McK]

Hello everyone, I'd like to share this build from last August.

Intro: Prior builds.
I built my first detector last April (2"x2" NaI(Tl)) which had 9% resolution. I experimented with several PMT's, various divider resistances (18 to 60+M) & tried split signal. The detector functioned well but the resolution was unchanged although the linearity improved. I built (3) more smaller detectors including a CsI(Tl) 20x20mm with resolutions varying from 8.5 to 12.2%.

Scionix build.
Seeking improved resolution I bought a Scionix 2"x2" NaI(Tl) Scintillator which duly arrived with a test certificate showing 6.2% resolution on their professional test rig - as tested by Luuk - this was a very encouraging result.
I put the scintillator onto a Hamamatsu R6231 (8.3% 57Co) with a 40M divider, Perfection Mica Mu-metal shield and fitted it into one of Stevens nice Aluminium housings that I had powder coated white (these now ship anodised).
I got an excellent 137Cs resolution of 6.5% averaged over 10 tests (192kB/s 24bit audio, PRA, GS1100PRO with results exported to excel then visio for ease of measurement). The results ranged from 6.39 to 6.55%.
The performance gains were immediately obvious compared to my other builds, the definition is much improved and the PMT works well over a wider voltage range.
The attached PDF shows the build, my earlier 3/ recent 5 detectors and some spectra.

I am very pleased with the build and the results considering it's an amateur set-up. It's a great detector to use.

PS Thanks to Luuk for his assistance and his detailed test results.

[iRad]

Hi Paul - Nice results and report. That Hamamatsu R6231 is one of my favorite PMTs and best sellers, along with its 3 inch cousin the R6233. I'm glad you put yours to very good use, coupling it with one of Luuk's (Scionix) nice crystals. Those PMTs are able to squeeze every bit of resolution available out of a good NaI(Tl) crystal. Cheers, Tom

[luuk]

Hi Paul,

Thanks for the report, that is a great result you got there from the 2”x2” very close to my test result.
And that with just amateur equipment compared to my professional amplifiers and mca’s .
You made an impressive set of nice home build detectors very very nice.

Luuk

[brehwens]

Hi Paul,

I second the previous opinions; very nice builds! Nice that you also put effort into a nice housing, it sure gives a "pro" feel to the probe!

[Sesselmann]

Ditto, very nice looking detectors and detailed report.

The powder coated detector looks very nice, something to consider...

Steven

[Paul McK]

Thanks for the feedback.

Yes the housings make the difference, some of those odd sized ones I made are only PVC pipe with a disc cut out of an end cap and glued into the bottom, then an end cap is pushed on the other end and the whole lot spray painted with a can of blue paint that turned out to be a close match to the blue anodised tubes. Even an old 35mm film canister cap worked for one and a cap from an old plastic container for another. The problem with PVC is I couldn't make it lightproof even painting it black first and had to heatshrink the PMT and divider instead.

The powder-coater near me did the tube for a good price but he only does white or black.