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Re: Problem detecting K-40

Posted: 10 Aug 2017, 21:48
by sgt_bear
Hi Steve, like i said before, the PRA looks similar to theremino.

I have now a idea what the problem could be, my sound-card chips full scale voltage is around 1.5V, but i have tried with a oscilloscope to measure the pulses, and some of them are >1.5V peak. So i guess in this case the sound card it self just puts out the max value... i try to lower the voltage now.

Re: Problem detecting K-40

Posted: 11 Aug 2017, 01:06
by sgt_bear
So actually this was the problem, the audio input just put out 100% (doesnt matter which volume you set in windows) so pulses over 1.45V got just read as 1.45V :'(

As a quick fix i lowered the voltage of the power supply around 50V and now no pulses over 1.45V happen. Also now reaings up to 3000 are possible... Attached are three images

1.) K40 Sample with Background in grey

2.) Reading of K40 "raw"

3.) Subtracted Background

Sure the peak is a bit off, i have to use the equalizers, but overall the spectrum looks like this:

Since the both spectrums on that page look different, i guess its a thing about detector and voltages..

But i guess it now works.. ?
I want to order at Spectrum Techniques soon, then i'll have a Co-60


Re: Problem detecting K-40

Posted: 11 Aug 2017, 02:35
by Peter-1
Hallo Johnathan,
If possible take a thorium preparation. Example an old mantle. Only in this way you can see if the system is linear.

Re: Problem detecting K-40

Posted: 11 Aug 2017, 04:55
by iRad
Johnathan - Good to see you got it figured out. Cheers, Tom

Re: Problem detecting K-40

Posted: 11 Aug 2017, 07:03
by sgt_bear
Peter, what are the dimensions of your detector?

Mine is 38x57mm, and i heard that bigger crystals do better at high-energy rays than small ones. Because i get signals beyond 1500keV, but not peaks like you do.
e.g. for x-ray flourescence all detectors have a very small size. Also this phenomen happens with geiger tubes, mica-window tubes won't detect as much gamma rays as steel-types do, because the rays just go through... don't know if its the same with Crystals

Your peaks look all relatively high, with my detector, the peaks are more wide and only the first ones are very high, the others are really small, like the first two are around 15k, the rest under 3k.

Re: Problem detecting K-40

Posted: 11 Aug 2017, 13:15
by Steven Sesselmann

Volume control is the most common problem, it would have been more obvious to me in PRA because the big peak would have been at arb.u 100 which is the last bin.

In PRA you also have the View >> Audio Input window which shows you the trace of the pulse, and if the pulses are hitting the ceiling the volume is set too high.

Glad you worked it out, and found the K40 hump.


Re: Problem detecting K-40

Posted: 13 Nov 2018, 06:48
by Springdream
Hello everyone,
besides the settings you mentioned I have the feeling the voltage is far to high. I also have an Scionix 38B57 (from Tom) and when I increase Voltage over 750V I get an increased number of false peaks (not 1460keV but somewhere lower that seems to be a false reading because of over excitation?). Anyhow, I am using it 690...750V.

Could you also share which voltages work fine for you and others?

Martin (Germany)