diy gamma ray scintilator detector - Page 1
Forum section: electronics / projects

author: ant17
author_rank: Regular Contributor
timestamp: November 29, 2013, 02:42:29 am
content: 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 onehttp://www.sphere.bc.ca/test/phototubes/+prutchi-paint-can-scintillator.pdfif some one could help i would be greatful

author: Kremmen
author_rank: Super Contributor
timestamp: November 29, 2013, 01:08:07 pm
content: Punctuation - the great innovation in parsing one's stream-of-consciousness into comprehensible units of communication. You should try it sometime.

author: Skimask
author_rank: Super Contributor
timestamp: November 29, 2013, 07:49:34 pm
content: Quote from: Kremmen on November 29, 2013, 01:08:07 pmWhere is that like button?

author: penfold
author_rank: Frequent Contributor
timestamp: November 29, 2013, 09:50:01 pm
content: 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

author: plesa
author_rank: Frequent Contributor
timestamp: November 29, 2013, 10:05:47 pm
content: Start herehttp://psec.uchicago.edu/links/pmt_handbook_complete.pdfFor alpha, beta, gamma, or x-ray is used bias tee see thishttp://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.

author: TerraHertz
author_rank: Super Contributor
timestamp: November 30, 2013, 02:29:25 am
content: Quote from: plesa on November 29, 2013, 10:05:47 pmThanks 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