FAQ -Update- Neutron detection methods (2015)

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Richard Hull
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FAQ -Update- Neutron detection methods (2015)

Post by Richard Hull » Thu Apr 30, 2015 9:44 pm

There are truly many ways to detect neutrons. In past postings it was noted that all neutron detection involved secondary events. As secondary events, such detection is usually effective only in rather large neutron fields. In short, it is very difficult to detect weakly emitting neutron events with a high degree of certainty without rather large expenditures of money or major construction and part collection efforts. This is quite apart from the effort in actual construction of a fusor. The neutron detection effort is a big win in and of itself and is often the would-be fusioneer's swan song, stopping many in their tracks. It separates the rich from the poor and true hands-on doers and hackers from the non-hackers. It sinks most of the DIY crowd, separating them from the true amateur scientist.

Add to the above the fact that virtually 100% of the folks who do finish a fusing fusor will produce very few neutrons on their first run. All who reach this point, wish to crown their extreme efforts with the vaunted and honored membership in the neutron club. Having a detection scheme capable of proving fusion is often an after thought that snags the feet of what might be a winner.

This post is an update of sorts that deals with those schemes capable of detecting limited neutron production, (fusion). I will put forward what I feel are the most sensitive methods in descending order of sensitivity.

1. 3He (helium 3) detection tubes. Much has already been written on this subject in this forum. This is the most sensitive and best method of neutron detection at very low levels. This is also the #1 most expense way to detect neutrons and, unfortunately, the method in which the amateur will have the least success even with ready cash to obtain a suitable tube and electronics. Once readily available for under $400.00 surplus, these now exceedingly rare detection tubes are rarely seen today at most any price due to the almost complete lack of helium 3 on the world market. Even with a tube, the electronics are special and a good electronics hobbyist or well heeled person will need to put forth a decent effort to make the tube work well. Still, luck and perseverance can create a win here.

1A. Russian 3He corona tubes. Ostensibly these are OK tubes. In practice, careful elelctronic shepherding is demanded in applying these tubes to succesfully work as suitable neutron counter detectors. A separate posting with data relating to using and interfacing these tubes can be viewed at...

viewtopic.php?f=13&t=10969

In general, these tubes, commonly found offered on e-bay, are a "pig in a poke". Do they work? Assuming they do, some special electronic skills may be needed to make the perform reliably.

2. BF3 (Boron Triflouride) detection tube. These were the detection item of choice during the Manhattan project and remain the current #1 tube still readily obtainable both in surplus and retail sales. Still rather pricey, but surplus tubes can be found in the $200.00 plus range. The same difficulty with electronics exists as with the 3He tube. However, this way is very doable for the well heeled or advanced electronics buff.

3. Boron lined detection tubes. These are, for the most part, rather ancient and are almost totally surplus items, but can often be found for less than $100.00. These are a bear to get working well for those who do not already possess or have access to a neutron source for calibration and electronic windowing. The electronics are only a bit less complicated but much more finicky of adjustment than the above methods. General Electric made most of these older tubes back in the 50's and 60's, but they made tens of thousands of them.

4. Large area silver activation schemes. While extensive comparisons are not yet done here, this method, in the right hands and correctly applied could possibly compete with the Boron lined tube and perhaps even a smaller BF3 tube. The good news is this can be a cheap and simple method though very involved with a good bit of DIY needed to hold down costs. A good deal has been written in a couple of postings on this method in this forum. The method involves corrugated Silver foil in a long strip, rolled up and immersed in a special beta scintillating liquid and a photomultiplier tube looking up through this liquid to count the beta particle released from neutron activated silver. The electronics is a good bit easier to work on and assemble than that of the BF3 or 3He tube.

5. BTI bubble dosimeters. This is a moderately expensive method of neutron detection ~$300.00. It is the absolute easiest of all possible neutron detection schemes. The bubble dosimeters, require zero electronics, zero skills and zero brains to use. They see only neutrons and herald their arrival and detection at various specific doses by producing highly visible bubbles within a bubble free liquid in a moderate sized test tube like device. They can be cleared of bubbles or "reset" after a measurement so that other measurements can be made. Sounds ideal doesn't it? Well, it sort of is. The real fly in this ointment is that in about 6 months, the bubble detector is as dead as a doornail and makes an intersting curio that looks cool, but does nothing ever again. Your $300 + investment is a worthless tube of goo. Try and get a 33 bubble per millirem or greater version to obtain the highest sensitivity to neutrons. Remember, if it doesn't bubble, you aren't doing fusion at all.

There you have it. There are few other methods of detecting low level neutron fields within the grasp of the average amateur. If you are truly interested in doing fusion, you must decide which of the above methods are for you.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ -Update- Neutron detection methods (2015)

Post by Rich Feldman » Fri May 01, 2015 1:59 am

I hope we can soon add neutron-sensitive scintillators such as LiI(Eu).
Bern showed us one in an off-the-shelf package, the NeutronRAE ii. May have been perplexed by our critical view of data sheets, in the absence of laboratory comparisons.
That instrument (or similar, such as the Scionix neutron detectors acquired by me and Rich Normand) would gain respectability if some fusioneer delivers a quantitative comparison of their counts (moderated and unmoderated) with those of another detector type. If the relative sensitivities (as observed) can't be reconciled with available literature, let the discussion begin.
Richard Feldman

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Richard Hull
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Re: FAQ -Update- Neutron detection methods (2015)

Post by Richard Hull » Fri May 01, 2015 3:57 am

Agreed. There will always be new stuff on the horizon, but for our purposes, until this stuff becomes easily available at lower prices and is acutally tested rather thoroughly in our environment, (fusion neutrons). We will not be further along than now. We may rest assured that the literature will always be favorable to sales and somewhat jumbled by our standards, confounding ready interpretation.

Before discussion begins, a good deal of testing within our environment would be nice and only then fine points brought to the fore related to its value to us.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ -Update- Neutron detection methods (2015)

Post by David Butz » Tue May 12, 2015 5:18 pm

Where do scintillation plastics, such as BC720 mentioned in the Fusion Tips found here, fit in to the list and practicality?

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Re: FAQ -Update- Neutron detection methods (2015)

Post by Richard Hull » Wed May 13, 2015 5:24 am

The efficiency of the BC720 is extremely low (below 1% for fusion neutrons). This means thats those critical, first pass, low level neutron tests will not make a statistically advantagous situation. My very first neutrons were detected with a BC-720 detector. Sadly, I know I was making neutrons in my first runs at 18kv, but the BC-720 didn't leave the statistcal level until I ... (1) gained a good deal of operational experience and (2) went well over 24 kv applied.

Richard Hester designed and posted a lot of great circuits a good while back for both PMTs and proportional tubes like the 3He and BF3 tubes. We even proved their effectivness at an early 2000 HEAS event when he brought a demo PMT system using the BC-720 or a work-alike detector to the event and used my fusor to show its effectiveness.

This thread was all about very low level detection methods common to the newbie first pass runs.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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