Repairing а BDFI-02 scintillation detector

[Yuri_M]

I've got a russian BDFI-02 scintillation detector which I've been trying to repair for a couple of months.
At first, the PMT was broken so I replaced it with another one (similar type, but such a replacement required making a new voltage divider). But, bad luck never comes alone, so there is a crack in the scintillation crystal too.
I'm trying to use PRA or Theremino MCA software for registering of spectra.
A simple op-amp current to voltage converter is used to connect the PMT's anode to sound card input (it also has a capacitor in the negative feedback circuit, so it works as a low-pass filter too). I can attach the circuit if needed.
Anyway, I'm not satisfied with the results: the spectra I obtain look so strange, so the general questions are:
-What I'm doing wrong (or everything's OK)?
-What should I do to improve the detector's performance?
-Is my scintillation crystal a garbage?

Some spectra are attached.

Thanks everybody!

[Sesselmann]

Yuri,

I agree, the resolution of your spectra don't look great. To diagnose your problem it would be helpful if you can provide screen shots including the Data Acquisition and control panel. There are several common errors that might cause such poor resolution spectra, one is when PRA is set to capture positive pulses with a negative pulse circuit. Maybe you can capture a screen image of the pulse from the Audio input window.

It's also possible that the crystal has absorbed some moisture which will easily cause the resolution to slide out beyond 15%

Steven

[Yuri_M]

Here are the screenshots

[Sesselmann]

Yuri,

Thanks, your settings look fine, you have a negative pulse and a negative threshold setting.

Your resolution might improve a bit if you tighten up the tolerance threshold, but I suspect your crystal is bad. The best test would be to try another detector.

Steven