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

Tom Hanley
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Re: Easy $150 Neutron Detection System

Post by Tom Hanley » Tue Mar 03, 2020 3:07 am

Just wanted to say, Thanks for the post Mark, helpful info.
I have scrounged up an old Ludlum Model 12 , it needed a cleanup, passes battery test and has a C type jack connector and it did come with a C type original cable. ( model 3's are possibly a better unit)
Electronic shops over here don't have adaptors ( possibly due to the age of it)and a "BNC Female to C Male Ludlum UG-636A/U Coaxial connector adapter" that have seen recently on EBAY cost Australian $43 and $29 postage from the US). it looks as though I might have to hack the terminal to an SHV connector. I have just gotten a CNM-11 tube also and will need to adapt to it too.
But its good to know that someone has already did some hack work, makes things a bit easier for guys like me less experienced.
Regards Tom

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Mark Rowley
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Re: Easy $150 Neutron Detection System

Post by Mark Rowley » Tue Mar 03, 2020 7:37 am

Hi Tom,
Thanks for the comments.
It's nice to see some benefit from the post. Swapping the C to a SHF is easy and I doubt you'll have any problems.
The 12 is a great meter but I cant attest to it's ability to operate in plug-n-play like the Model 3. The 12 has threshold control that may need adjustment for it to work.

Mark Rowley

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Richard Hull
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Re: Easy $150 Neutron Detection System

Post by Richard Hull » Tue Mar 03, 2020 2:30 pm

I have 5 various Ludlums on hand here and the #1 thing I do once I purchase them is to test them, if OK them #2 is putting a common BNC connector on them. After mounting the common BNC, I put a nice big ole wad of silly-cone HV putty over the inside HV solder connection at the rear of the BNC. Haven't had any issues doing this.

Richard Hull
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