Easy $150 Neutron Detection System

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Mark Rowley
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Easy $150 Neutron Detection System

Post by Mark Rowley » Tue Jan 28, 2020 8:08 am

Restoring old scintillators and Geiger counters has been a hobby for quite a few years and resulted in quite the assemblage of ancient yet operational detectors.

Being the case, I decided to take a dusty 1st generation Ludlum Model 3 analog meter and pair it up with a $50 Soviet CHM11 boron type neutron detector (I bought the Ludlum for $100 several years ago).

The only prep work I completed was adjusting the voltage from 900v to Corona Mode voltage of around 750v.

First test with hot radium and gummite sources showed total gamma rejection. Second test with a weak AmBe source gave me the expected ~15cpm.

I then briefly fired up the Fusor for a quick and dirty run of about 173k isotropic n/s (evidenced by 5 BTI bubs in 150 seconds).

During that run, the Ludlum passed the test by detecting neutrons at the expected voltage of near 20kV. At 32kV I let the neuts click away on the Model 3 until I removed the boron tube from the paraffin moderator. Conducted this back and forth test several times with consistent results. At 32kV, xrays were present and were not detected by the tube.

Tbh, I expected this to work but was totally surprised byits simplistic / turnkey ease of operation.

The Model 3 is obviously not a digitally timed ratemeter but one can still be confident with its ability to register via the dial meter and audible clicks.

At least for beginners, this arrangement could be an easy way to keep the costs down and have a viable and simple to assemble neutron detection system.

Mark Rowley

Lukas Springer
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Re: Easy $150 Neutron Detection System

Post by Lukas Springer » Tue Jan 28, 2020 12:46 pm

I'm a bit surprised your ludlum managed to detect the events, in my experience the model 3 need a small notification for a lower trigger.
Also 750V is not the "Corona mode voltage", but only the ignition voltage, meaning that the detector is in corona discharge *above* that voltage.
https://www.youtube.com/watch?v=nwrPYnFZ0ps

This was my attempt at your experiment a couple of years ago, worked just fine!

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Mark Rowley
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Re: Easy $150 Neutron Detection System

Post by Mark Rowley » Tue Jan 28, 2020 3:48 pm

Good point on the technical side of where ignition and corona mode voltages begin and end. Much higher than 750v, the CHM11 begins to pick up noise and other unwanted events. No doubt this is a characteristic with the Soviet boron tubes but in the grand scheme of things, its a total non-issue.

Later today I'll try the same experiment with another dusty relic in the shop and report back.

I see this as a potential game changer for newbies or those struggling with neutron detection.

Model 3 plus CHM11 provides solid noise-free neutron detection....$150 and you're off and running!

Mark Rowley

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Mark Rowley
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Re: Easy $150 Neutron Detection System

Post by Mark Rowley » Tue Jan 28, 2020 8:13 pm

Just pulled another old Ludlum Model 3 off the shelf, dropped the voltage to 750, hooked up the CHM11, and worked flawlessly.

Just for fun I swapped in the smaller Soviet CHM14 boron tube which worked equally well.

No Fusor noise, full rejection of gamma and xrays on both tubes and Model 3’s.

Shown is a pic of the CHM11/Model 3 with a paraffin moderator containing a weak but detectable Am/Be source.

Mark Rowley
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Jim Kovalchick
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Re: Easy $150 Neutron Detection System

Post by Jim Kovalchick » Tue Jan 28, 2020 8:23 pm

Mark,
I'm curious, did you use an in-line resistor or coupling capacitor?
Thanks,
Jim K

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Mark Rowley
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Re: Easy $150 Neutron Detection System

Post by Mark Rowley » Tue Jan 28, 2020 8:46 pm

10meg resistor. No cap.

Mark

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Mark Rowley
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Re: Easy $150 Neutron Detection System

Post by Mark Rowley » Thu Jan 30, 2020 3:23 am

Put together a 10 minute vid on the arrangement showing it's simplicity.

https://youtu.be/cCRk45gLEmc

Mark Rowley

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