finding plateau voltage

Scintillation crystals, PMTs, voltage dividers etc...
keuleeule
Posts: 48
Joined: 31 Oct 2016, 09:09
Location: Hamburg/Germany
Contact:

Re: finding plateau voltage

Cath - Anode 4,47MOhm
Remember V(real) = V(display) * (a)/(a+b)
Where a = divider resistance and b = load resistor resistance
V(real) = 730V * 4,47M/4,47M + 1M
= 596V
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keuleeule
Posts: 48
Joined: 31 Oct 2016, 09:09
Location: Hamburg/Germany
Contact:

Re: finding plateau voltage

Ok, if there is nothing on the output, only Oscilloscope, the 200mV are gone.
I tried to copy long therm, 5s/div
only 20mV peaks... have a look to the picture...

Steven Sesselmann
Posts: 723
Joined: 27 Apr 2015, 11:40
Location: Sydney
Contact:

Re: finding plateau voltage

Kolja,

With that divider (5.2M Ohm) the voltage on the GS-PRO display will read about 20% higher than actual voltage, so when you are running at 1350V the real voltage is only around 1100V.

This reason and also the limited current available from the USB bust, is why I recommend a 12 M Ohm divider.

PS: Can you also confirm that your sound card is not inverting the pulses. It is a common mistake to set the pulse height threshold with the wrong sign, i.e. if the pulse is negative your threshold in PRA must be set to a negative number (-0.3) else it will be looking for your pulse above the baseline instead of below.

Steven

Steven Sesselmann
Posts: 723
Joined: 27 Apr 2015, 11:40
Location: Sydney
Contact:

Re: finding plateau voltage

Kolja,

If you like we can hook up for a quick Skype or Facetime call, then we may be able to narrow down the problem quickly.

Steven

keuleeule
Posts: 48
Joined: 31 Oct 2016, 09:09
Location: Hamburg/Germany
Contact:

Re: finding plateau voltage

yes yes yes, Steven showed me how to adjust the pre-amp volume and showed me that my soundcard SoundBlaster X-Fi HD USB does a bad job...
Now I get real spectra, still struggleing with calibration, but my day just starts, so I can run several tests now.

My first impression is worth it, as 15years ago I collected smoke detector sources containing Ra, each one had two sources in and by mistake I found 5 metall plates in my container - so one too much.
Which one is Am instead of Ra? ok, that one would be quite easy, but now I was able to find exactly the right one. Perfect.

I will share the Spectra when Im done...

Kolja

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