Tap Circuit for a Ludlum 3503

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Will Brown
Posts: 2
Joined: 05 Apr 2017, 04:26

Tap Circuit for a Ludlum 3503

Post by Will Brown » 05 Apr 2017, 05:08

Hello All,
I bought a Ludlum 3503 Gate Detector from eBay a few weeks ago and wanted to use that as a High Voltage source to run a Hamamatsu R6233 PMT with a Bicron 412 Plastic Scintillator. I am beginning to assemble the R6233 from iRad, and the plan is that once it's assembled, connected and working with the Gate Detector, I would tap the circuit at the appropriate spot and use the signal there to feed it into my laptop with PRA or some other software.

Still being a bit confused about how the HV coming off the PMT is separated into the various KeV's pulses in the software, I'm going to have to take it on faith. (light pulse from the Bicron 412 strikes the semi-conductor cathode, ejects an electron, is multiplied through the dynodes to the anode, the "glob" of electrons goes through the circuitry, etc. etc. How does it determine the KeV strength corresponding to the initial particle ejected from the radioactive source if the cathode is semiconductor (digital, go, no go) and the HV is constant from pulse to pulse?)

I found a circuit from an brilliant engineering type that I'm going to incorporate, tapping the circuit as he did with his Bicron Spectrometer just after the first capacitor. (see pic). My question is: Are the 2 blue arrows in the jpeg the right place to tap? Bonus question: Is the circuit he designed going to work?

Spectrometer Circuit.JPG
Circuit to use to tap into 3503
Spectrometer Circuit.JPG (107.23 KiB) Viewed 1539 times
3503 tap.JPG
Blue Arrows indicate possible tap points
3503 tap.JPG (75.96 KiB) Viewed 1539 times

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Steven Sesselmann
Posts: 611
Joined: 27 Apr 2015, 11:40
Location: Sydney

Re: Tap Circuit for a Ludlum 3503

Post by Steven Sesselmann » 05 Apr 2017, 19:54

Hi Will,

More or less as you describe, the PMT anode is positively biased at around 800 volts via a load resistor (usually around 1M ohm) so when the glob of negatively charged electrons (as you describe it) collides with the anode, the voltage briefly drops between the anode and the load resistor. This voltage drop travels as a wave back up the line where it gets picked off by a coupling capacitor, imagine the coupling capacitor as a person eavesdropping on a conversation through a closed door, no air actually travels through the door, but you can still hear what's going on.

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

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