Help with calibration

Scintillation crystals, PMTs, voltage dividers etc...
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wbelisle
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Joined: 13 Oct 2016, 15:59
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Help with calibration

Post by wbelisle » 27 Jan 2017, 15:22

Sorry if this has been covered before, but can someone please either describe for me or point me to a link that describes how to adjust the voltage on my GS-1100-Pro for best response? I've read many of the posts on this forum and I keep seeing references to a procedure but I can't seem to find any solid instructions. Perhaps they're right in front of me but I don't see them.

I have built a scintillation counter using a 32-mm by 122-mm NaI(Tl) crystal and have it mated with a Hamamatsu R9420-20 photo-multiplier tube. I also have a few sources I can use but the procedure eludes me. The datasheet for the PMT says it runs at 1400 volts but from what I've read I don't need the voltage that high. Any help is appreciated.

Thanks!
Bill Belisle
San Francisco, California

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Steven Sesselmann
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Location: Sydney
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Re: Help with calibration

Post by Steven Sesselmann » 27 Jan 2017, 17:27

An brief introduction in the introductions forum would be great, so we can be polite and address you by name, it's one of our forum rules.

Finding the working voltage plateau for a given PMT is done by recording the count rate at different voltages and looking for a plateau where the count rate is relatively stable. This is easy to do with PRA as it has a counting rate over time log.

I suggest warming up the detector for a couple of minutes before beginning the recording, you then start at something like 500 volts and log the count rate for a minute or more, then adjust the voltage up by 50 volts every couple of minutes.

Initially you will see the count rate increase as you adjust the voltage up, but then you will reach a plateau where the count rate remains relatively flat, before it starts rising again.

Your optimum PMT voltage is somewhere in the middle of this plateau.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

wbelisle
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Joined: 13 Oct 2016, 15:59
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Re: Help with calibration

Post by wbelisle » 28 Jan 2017, 02:17

Thank you, Steven. I will try that procedure as soon as I can.

Sorry about the introduction confusion; I had created a post in the Introductions section last week titled "Introduction and a few questions" posted 16 Jan 2017, so I thought that was taken care of. However, I just noticed that I hadn't include my name in the previous post.

Regards,
Bill
Bill Belisle
San Francisco, California

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Steven Sesselmann
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Joined: 27 Apr 2015, 11:40
Location: Sydney
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Re: Help with calibration

Post by Steven Sesselmann » 28 Jan 2017, 10:54

Bill,

Sorry my mistake, I didn't see the introduction. In the user control panel you can add a signature which will appear under the fine grey line on every post.
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

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