Easy $150 Neutron Detection System

[Pablo Llaguno]

Mark I noticed in your video that you have a "The Nucleus" counter. I also happen to have one and a Nuclear Chicago BF3 tube.

IMG_0009.jpg (154.22 KiB) Viewed 11217 times

Since it has adjustable voltage, could I set it up at 750V and start counting nuetrons? I don't have any specs on my tube (and I searched without success) but I can have access to a neutron source. One issue about the tube is it's connector, it is a UG-59A/U coaxial, any ideas on how to fit this to the BNC of the counter?

[Mark Rowley]

Hi Pablo
I’ve never tried it with the Nucleus. Only thing I use it for is to count indium activation results by driving a standard LND 7311 pancake tube. I know those units work good with scintillation type detectors but I can’t attest to their suitability with any neutron detectors. The Nucleus only has a voltage control, nothing else. Internally it’s all solid state with none of the standard calibration controls found on the more common meters like a Ludlum or Eberline. Tbh, I’m very doubtful if it’d work. But nothing is gained without trying. Just remember, the arrangement I suggest has a very narrow set of guidelines. Ludlum Model 3 and either a CHM11 or 14 tube. Beyond that, you’re in uncharted waters.

Only suggestion on the connector is to try to source an adapter or build your own cable.

Mark Rowley

[Sarmad suseyn]

Hi Mark Rowley
Thanks too much for your video.
I tried to copy your settings (hopefully no copy right issues )
But without luck.
I have ludlum model 3 and Russian snm-14 tube.
I setup the voltage to 750v and i added 10m ohm resistor to the top part(positive) . And im not getting any readings.
Im using about 120 smoke detector americium (120 μCi)
With berylium chunk as a neutron source. And hdpe blocks as moderator. Any ideas?
Thanks in advance

[John Futter]

Sarmad
you have not completed your registration on this site, and you are not following the site rules
your first post must be in the "Please introduce yourself" forum

otherwise you are starting to act troll like

[Mark Rowley]

Hello Sarmad,
I’m doubtful that the regular hardware store variety smoke detector sources (even a bunch) will provide a strong enough neutron source to be readily detected above background.

Couple questions...
1) How did you wire the detector to the Ludlum? The connection points between the cable and the tube should be as short and insulated as possible. No alligator clips or long wires as everything should be a direct connection.

2) Are you registering any background counts? If so, how many counts over 5 and 10 minute intervals?

We recently had one case with a CHM11 where there was some possible internal gas pressure difference in the tube causing issues with the resistor value. The only way it was able to work was the total removal of the external resistor (there’s still an internal 3.3m resistor in the model 3). Even cutting the value of the external resistor in half did not help. Now of course this is a last resort scenario and may not be relevant to your situation.

If you’re getting background counts then it’s just a matter of your neutron source being too weak.

As an important Fyi, it’s a common misconception that all one has to do is attach a few Am241 buttons to a block of beryllium and it’s neutron city. Not the case. You may get a few but the amount will be ultra low and quite often much to low to easily detect with a boron type corona tube including a wide variety of other neutron detectors.

Mark Rowley

[Jim Kovalchick]

Mark,
I am testing a CHM 11 with a 10 Mohm in line resistor, 2 foot MHV to BNC cable, BNC to C adapter, to a Ludlum Model 2200 scaler at 750 V.

At a zero threshold there was of course a lot of noise. I raised the threshold just a tad and the noise became quiet. At background, the counts look random and distinct. There are occasional background events of more than one count. All this looks right to me. A strong radium source does not influence the count rate at all.

I expect to do a test with the fusor later, but my question for you is about background. What is the count rate you experience? A 10 minute run yielded 131 counts. 13 cpm seems high to me for a CHM 11.

Update: fusor run complete. The CHM 11 performed very well. It's count rate was 25% higher than my old Nancy Woods BF3 tube in the PNC. Moderator removal test passed with flying colors. No issue with xray interference. This may become my permanently installed indication for my fusor.

Thanks
Jim K

[Richard Hull]

No experience with the russki tubes. However, my large 3He in water moderator reads 6 cpm on a low day and 12cpm on a bizarre sun day and one time 22 cpm during the great CME some years back where I could see the Aurora here in Richmond. The norm is 7-9 cpm. I think your background is OK. (assuming it is in a moderator).

Richard Hull

[Rich Feldman]

Here are some more numbers about count rates.
And a question for Mark about the activity in his "weak" AmBe neutron source.

My home-made AmBe source, with roughly 70 uCi of Am, gave a clear signal with a conventional BF3 tube.
About 2 counts per minute, above background of about 1/2 count per minute.
viewtopic.php?f=13&t=12649&p=86307&hili ... ier#p86287

It was my first crude attempt with that source. Next step hasn't happened yet, because I left the detector at work on March 12, and have not set foot there since that day.

It's my understanding that commercial AmBe neutron sources have the relevant elements powdered and mixed together,
so they are naturally a few times more efficient than anything easy to make with separate alpha sources and Be metal.
(Be powder is the natural precursor to all Be in solid shapes for making engineered parts.)

[Jim Kovalchick]

My home lab is about 16 feet above sea level in Myrtle Beach, South Carolina. I would have thought that background would be relatively low at this place vs most other places in the country. Also, perhaps this latitude may have less neutron producing cosmic rays.

My detector is surrounded by 2 inches of HDPE on all sides.

I was expecting more like what Richard reported or less.

[Mark Rowley]

Jim
Glad to hear it’s working good for you.
Using the Ludlum 2221, my CHM11 averages about 1cpm. Two 10 separate 10 minute counts yielded 9 and 10 events each.

Rich,
I forgot to update the AmBe remark in the earlier post. Alan and I were discussing static neutron sources a couple months ago and I realized this error. It’s actually a weak PoBe source being a Nuclespot Static Eliminator disc I purchased new around August 2018. It was almost at 17 months of decay when I ran the test last January. Configuration was just the typical Be block placed over the Nuclespot screen.

Mark Rowley

[Jim Kovalchick]

Thanks Mark. I tried a couple iterations of threshold adjustments and found that another tenth of a ten-turn got my background down to 1 to 2 cpm. Because there is no preamp, I'm afraid to move the threshold to far. A proportional tube dip will be too small to see otherwise I think. Fusor run later to test with known neutrons.

[Jim Kovalchick]

My Ludlum 2200 threshold is set at 0.8 on the ten-turn, and voltage is 750. Background is around 1 cpm.

Today I packed the CHM 11 into a piece of 4 inch poly drain pipe with HDPE granules. Parked up next to my fusor running at -37.5 kV and 8 mA, the detector read 2000 cpm on the rate meter. I think with some adjustments to geometry it could improve, but at this point I really just need to set a consistent benchmark that i can use as a gauge of fusor performance.

These Soviet tubes seem to be immune to xrays when set up the way Mark advises. Performance, cost, and size make these tubes an easy choice for permanent fusor neutron detection.

[Richard Hull]

I am glad to here you have it working. Good going. The higher a neutron count you can get versus background, the better. (more efficient neutron detection) This allows for detecting very small neutron counts from very weak neutron sources as well as small differentials in small, weak sources.

Richard Hull

[Jim Kovalchick]

Richard,
I doubt the CHM 11 tubes will be very useful for low neutron counts. Maybe I will try some low voltage, low current ops to find out. I'm not real keen on running my fusor too low voltages because with deuterium the pressure is hard on the turbo. I may just shut it off.

I was really thinking of using the CHM 11 tube as more of a 'speedometer' if you will. I will permanently affix it to the fusor such that at the high end I will have a measure of performance and benchmark for experiments like activation.

For much lower neutron counts I intend to use my lithium 6 paddle. That detector was intended to rival a whole bank of He 3 tubes. I have yet to fully explore it's full capabilities. I think it may even be able to pick up low count rate alpha-n reactions from non-fusor experiments I'm interested in doing. For fusor work I found that it's size made it a little impractical and more importantly, it was very sensitive to pile up of the numerous xrays even when I shielded.

Jim K

[Marko Kuzmanovic]

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

https://youtu.be/cCRk45gLEmc

Mark Rowley

It shows the video as private?

[Mark Rowley]

Somehow it was accidently put on private mode. Fixed, it should work now.

Mark Rowley