Help wiring a crismatec 1.25" NaI (Ti) scintillator.

[James Luck]

Hi James,
Did you ever get that detector working? I recently acquired a similar one with slightly different labeling but still a 32 SPE 50. On the label it lists the PMT as a Hamamatsu R268. I'm probably going to try powering it up with the signal out to an oscilloscope and slowly ramp the voltage up to see what I get.

Since my update have you had any Luck?

the furthest ive found so far is the "32 SPE 50" relates to a medical isotope station, for measuring activity and daughter concentration. but i cant recall the exact name currently i guarantee when i was looking last i put away a document on the setup though that's missing as of now.

i am familiar with that pmt which is interesting, just wish i knew how it was wired still.

-J Luck

[James Luck]

Hi James,
Did you ever get that detector working? I recently acquired a similar one with slightly different labeling but still a 32 SPE 50. On the label it lists the PMT as a hamamatsu R268. I'm probably going to try powering it up with the signal out to an oscilloscope and slowly ramp the voltage up to see what I get.

Hi Addison,
I finally got around to messing with the one I had. I got mine to work and thanks to a help of a friend who pointed out the circuitry on the board looked to be for both signal processing aswell as gain control.

He pointed out two smd resistor values, which connect anode to dynode 7 and dynode 7 to dynode 6.
Man do i really feel dumb, but smd is nothing near my knowledge, especially reading and component nomenclature.

Anyhow I took off the circut board and ran the required resistor values, plus added a singular connector to work off of.
After such I did test fire and she worked, the voltage range seems to be 450v-1kv(ish) at 1kv it plateaued and never gained anymore counts up to 1.6kv.

If your still messing with yours and want help I'll lend a hand, if not and you've aready got it working congrats your a bit smarter than i.
Take care, James.

[Sylvain]

Hello,
I'm taking the liberty of taking up this thread because I also have 32SPE50 detectors. As indicated in this thread the tube would be an Hamamatsu R268. I connected a very simple high impedance voltage divider (10MOhm between each dynode and 1Mo between D11 and the anode as recommended here https://www.theremino.com/wp-content/up ... rs_ENG.pdf page 33). I get a pretty good resolution, but there is a big linearity problem, as if the spectrum was "compressed" in the high energy part. I thought it could be a saturation of the amplifier, but it must not be that. Do you think it could be the voltage divider? A have two tubes, both with same issue.
Best,
Sylvain

[Svilen]

Hi Sylvain, I don't know how bad it is, since no detector is linear through the whole range, but did you try to adjust the HV a bit?

[Sylvain]

Hi,

Thanks for your reply. To give you an idea of the situation here are two spectra obtained with a crystal of LYSO.
The first one is obtained with Theremino MCA without calibration, simply centered on the peak at 202KeV. We can see very well the peaks (supposed to be) at 202, 307 and the sum around 510 KeV but everything is very compressed (almost impossible to well calibrate with theremino).

lyso-theremino.png (59.61 KiB) Viewed 802 times

Here is also a spectrum obtained with the PRA and a quick calibration. The calibration works well (look at the scale), and it is usable, but I still find it strange to have such a non-linear response.

lyso-pra.PNG (10.57 KiB) Viewed 802 times

What do you think of these spectra ?

Best,
Sylvain

[Svilen]

You didn't say if you tried to find the voltage where the detector is most linear, it could be that it is not optimal, maybe too high... if you didn't - you can use this simple excel table tool from this thred here:
viewtopic.php?f=17&t=702