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mini CsI(Tl) PMT detector build

Posted: 15 Sep 2015, 23:27
by Paul McK
Let me share the recent build of this mini detector

I had several 10x10x10mm CsI(Tl) scintillators to experiment with using a PIN diode. Instead I noticed a suitable PMT on ebay and built a mini PMT based detector which seems to work quite well considering. The R5070A PMT is only 46mm long but has a 21diam photocathode, importantly a 300 to 900nm range, 10 stages and is linear focused. I prepared the crystal by lightly sanding the sides then spraying them matt white. The PMT was fitted with a Mu metal shield, the 72M voltage divider + 3 caps was soldered to the socket and then everything covered in heatshrink. The crystal was then attached to the face and wrapped with electrical tape. The completed detector was placed inside a painted (not lightproof) plumbing pipe of a nom 32mm OD. Refer attached pics.

First tests showed a background count of just over 300CPM which seems excellent so far so good. It prefers around 950V and 90% audio gain.

I ran Ra, Cs and Th spectra in a lead castle which seemed to give reasonable results for the type & size of the crystal. Refer the attached pics. The resolution is 8.8% (137Cs) measured by exporting the PRA data to excel.

The purpose of the build was to make a mini detector for a portable geiger counter that gives a better count rate than a geiger tube, I originally tested it with 2 crystals to increase the counts but it works OK with one. It proved to be quite an interesting exercise and 1 of 4 different detectors I built in August.


Re: mini CsI(Tl) PMT detector build

Posted: 16 Sep 2015, 15:31
by Steven Sesselmann

Nice little detector, and the spectra look quite respectable too. I too have been playing around with PIN diodes, but so far I havent had much success, your idea of using a small PMT is much more reliable, and becomes a simple plug and play job.

When I eventually get the PIN diodes working I will share how I did it, but for now it's just one of those projects I go back to when I have nothing better to do.

Thanks for sharing.