gamma spectrometer signal

[pawel1010]

I've built gamma spectrometer with CdWO4 scintillator crystal connected to diode with unknown parameters. The crystal dimensions are 30x7x5 mm. The output signal are positive pulses with heights in range 0-2 volts amplitude and 150 µs width at the bottom. Here is example output pulse and software discussion link: viewtopic.php?f=7&t=986. The circuit scheme is here:

spectrometer_circuit.png (38.09 KiB) Viewed 1225 times

The output signals look like this: https://youtu.be/J5O0gaWGp_o
Is the signal ok for Theremino or PRA? Using Theremnio I get only one peak for radium source.

[Sesselmann]

Pawel,

From what I can tell, the output from your circuit should work fine with a sound card MCA. The maximum pulse height of 2V might need attenuation as most sound cards have a dynamic range of 0-1.4 volts (some only 1.2V). The pulse length of 150 µs is perfect, at 384. kHz sampling you can even shorten it a little.

I suggest PRA because it adapts to your pulse shape when you run the Pulse Shape Acquisition.

Steven

[pawel1010]

Steven,

I've reshaped pulses to fit them in range 0-1.4 volts. I also added zero pole cancellation. Now they looks like this:


I didn't know how to set correctly Data Acquisition and Analysis, so I set some parameters.

Then I get this for radium-226 source after I clicked Start Pulse Shape Acquisition.


I think the problem is that the Data Acquisition and Analysis parameters are wrong. How the parameters should be set?

[Sesselmann]

Pawel,

The pulse on your oscilloscope looks perfect, but the pulse on your audio input window looks very noisy.

My guess is you are listening to the internal microphone, not the detector, please check the Audio Interface is set to USB AUDIO CODEC - 384 kHz - 16 bit - Left channel.

Steven

[pawel1010]

Steven,

I reduced system sound volume to 50%. Since then, the pulses have shown. With higher volume then 50%, the tops of the highest pulses are horizontally cut. The check source is radium-226.

The spectrum still doesn't look correctly:

[Sesselmann]

Pawel,

I have no experience with CdWO4 scintillator, so I don't know what resolution to expect. It does seem very strange that there is no information in your pulse height histogram.

If you can measure pulses on your scope and you are sure you are recording the correct channel then there is no reason why it shouldn't work.

NOTE: In the screen shot above the pulse height discriminator is set to 10 arb.u, this makes me suspect you were running Pulse Shape Acquisition and not Data acquisition.

Steven

[pawel1010]

To find the solution of problem I recorded output from my spectrometer with program InTune:https://drive.google.com/file/d/1BG3Pcb ... sp=sharing

Please look at this pulses, I would be very grateful for help with filtering radium 226 gamma spectrum from this .wav file if it is possible.

[Sesselmann]

Pawel,

I opened your file in Audacity, I can see you have lot's of small pulses on a relatively noisy baseline noise < 0.5 arb.u, so the noise is not your main problem, although great if you can filter it.

The spectrum shows most of the pulses piled up on 5 arb.u., I'm not sure, but maybe you just don't have enough gain from the PMT.

I also notice how the pulse width spread is large, normally when using pulse shape method the pulse width is rather more constant.

Steven

Small pulse

PRA screenshot

[pawel1010]

Steven,

After the closer inspection, I found that was a light leakage. I sealed the box and increased 5 times amplification of the signal due to your suggestions. The current recording after the modification is attached here: https://drive.google.com/file/d/126HpkT ... sp=sharing.
Do the pulses need more amplification?

[Sesselmann]

Pawel,

Considering it is sampling at 48 kHz, the pulses look about right.

Count rate seems low for a scintillation detector, but maybe you are shielding out background... don't know?

Steven

Audacity Screen Shot