Author Topic: diy gamma ray scintilator detector  (Read 4919 times)

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Offline ant17Topic starter

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diy gamma ray scintilator detector
« on: November 29, 2013, 02:42:29 am »
hi guys i found a plans for a gamma ray scintillation detector its designed for a cdv 700 old style geiger counter which but i wanted to get a measures voltage the changes with the number of scintillation but the voltage is to high for my multimeter or scope but my main question is what is the normal way of measuring a photo multiplier tube out put at the anode because if i hooked a opamp up to it to amplify the the the high voltage would destroy oh and here is the link my tube is exactly the same one http://www.sphere.bc.ca/test/phototubes/+prutchi-paint-can-scintillator.pdf if some one could help i would be greatful
 

Offline Kremmen

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Re: diy gamma ray scintilator detector
« Reply #1 on: November 29, 2013, 01:08:07 pm »
Punctuation - the great innovation in parsing one's stream-of-consciousness into comprehensible units of communication. You should try it sometime.
Nothing sings like a kilovolt.
Dr W. Bishop
 

Offline Skimask

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Re: diy gamma ray scintilator detector
« Reply #2 on: November 29, 2013, 07:49:34 pm »
Punctuation - the great innovation in parsing one's stream-of-consciousness into comprehensible units of communication. You should try it sometime.
Where is that like button?
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

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Offline penfold

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Re: diy gamma ray scintilator detector
« Reply #3 on: November 29, 2013, 09:50:01 pm »
Indeed one method is to measure the current at the anode, except that's not always practical as it requires separate connections for the HV bias and signal.  Given that, normally, one would be measure discrete pulses due to individual scintillation events, this can be done at the cathode.
The HV is connected to the PMT via a series resistance that gives a voltage proportional to the PMT current (this will be a sum of steady DC drawn by the bias chain and the photocurrent that flows from cathode to anode (amplified photoelectrons)), because the scintillation events produce small pulses of light, the photocurrent will also be made up of small pulses, these are normally AC coupled via a capacitance from the series resistance to the detector, and is probably how the cdv rate meters operate as the PMT is operating similar to a GM tube.

As far as measuring these voltages, you need a high voltage probe, these are normally made up a string of high value resistors acting as a potential divider, they both attenuate the signal to a measurable level and increase the resistance load on the source.  Measuring the pulses should be quite easy if you couple the system to your scope via a high voltage capacitance with a value in the 100nF region
 

Offline plesa

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Re: diy gamma ray scintilator detector
« Reply #4 on: November 29, 2013, 10:05:47 pm »
Start here
http://psec.uchicago.edu/links/pmt_handbook_complete.pdf

For alpha, beta, gamma, or x-ray is used bias tee see this
http://www.diyphysics.com/2012/02/20/simple-d-i-y-bias-t-for-scintillation-probes-with-single-connector/
I wll prefer the separate connection for HT and for signal out and integrate the transimpedance amplifier into the can ( e.g OPA657 is cheap and good for this)

The voltage divider for photon counting can have quite different construction ( check datasheet for voltage dynodes ratio and the last dynodes voltage)
Beware qoute old PMT's on ebay, the main reason is the vacuum level inside tube which affects the noise level/dark current.

 

Offline TerraHertz

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Re: diy gamma ray scintilator detector
« Reply #5 on: November 30, 2013, 02:29:25 am »
Start here
http://psec.uchicago.edu/links/pmt_handbook_complete.pdf

For alpha, beta, gamma, or x-ray is used bias tee see this
http://www.diyphysics.com/2012/02/20/simple-d-i-y-bias-t-for-scintillation-probes-with-single-connector/

Thanks for the links!
Especially this, which will be many hours of happy reading for me: http://www.diyphysics.com/
The downside - trying not to get sidetracked from existing projects.

Err... OP, seriously, do you talk like that? Too much coffee?
My suggestion: google history of punctuation pauses in speech

Collecting old scopes, logic analyzers, and unfinished projects. http://everist.org
 


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