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 »

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

Post by Rich Feldman »

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.
All models are wrong; some models are useful. -- George Box
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Richard Hull
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Re: FAQ -Update- Neutron detection methods (2015)

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ -Update- Neutron detection methods (2015)

Post by David Butz »

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

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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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ -Update- Neutron detection methods (2015)

Post by Richard Hull »

This is a further update for 2020 related to neutron detectors. A nice clean table of detectors is found in the U tube video at

https://www.youtube.com/watch?v=nHpfAis7aCU

I have screen captured the table below for those who wish to study it at leisure as the URL above may be ephemeral. This is a great catch-all table and really spills the beans on all detection methods for neutrons, but leaves out bubble detectors which we have talked about in the FAQs here and many postings within the general forum here. The great thing about this table is give all the straight dope on the various pluses and minus points on each detection method. 3He as we all know is the absolute best with BF3 a close second. Everything else is less, but perhaps some of them are either easily located or a cheaper solution. However the low efficiency items are to be shunned for the amateur fusioneer as those just starting out usually have very low fusion rates, (neutron output).

Yes, special plastic scintillators look great by efficiency, but you need a 2-inch thick chunk of the neutron sensitive plastic to cover whatever sized PMT you might have and the gamma and x-ray peaks at a certain intensity, which is rather low, will foul you neutron counting as the signals can't be discriminated out. These are tricky to work and will consistently lie to the neophyte user in x-ray and gamma fields. The fusor will throw out quite a rather significant x-ray blast above 20kv. (about the point where neutron production is just within common measurement range of a 3He detector. I amateur hands, a simple neutron plastic scintillator is not to be desired. The Bicron fast neutron plastic scintillator (BC-210), is very special and may be considered equal to a hornyak button on the table. The BC-210 is also immune to rather intense gamma a x-ray radiation.

Newbies are exhorted to view the video and listen to the discussion which details the table.

refer to this table image below as needed to reference all future neutron detection situations where a specific type of detector is needed.

Richard Hull
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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
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The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ -Update- Neutron detection methods (2015)

Post by Mark Rowley »

Seems like a lot of work when one can buy a used Ludlum Model 3 and attach a $50 CHM11 or CHM14. Easy as can be.

viewtopic.php?f=13&t=13216

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

Post by Richard Hull »

Yet a further update on noise in neutron counting.

Noise is a function of detector volume and the ability to remain insensitive to outside radiations, (usually gamma and X-radiation), while having a very good detection efficiency for neutrons per unit volume.

1. The larger the volume, regardless of all other factors, the more likely noise can creep into neutron measurements.

2. Given a certain detection efficiency, the electronic response or signal size is critical to noise issues. A fempto-coulomb neutron detection signal can be a noise nightmare, while a rather robust 1 micro-coulomb signal might have far fewer noise issues while counting neutrons.

3. Pulsed neutron sources are the worst to try and count as large pulsed electrical energies are usually the order of the day required to generate measurable neutrons. RF and high EMF induced pulses can enter circuitry in the neutron counter or its cabling.

4. Noise, coupled with high background radiation events, limit all neutron counting efforts near what might be termed the floor or even the basement of reliable neutron counting efforts.

Unless you are very familiar with your neutron detection system which has a high efficiency, and know its limitations, any neutron counting below a fluence of 0.2 neutrons per second, per square cm might be a floor that would be tough to read with accuracy. (this assumes a non-pulsed, continuous and stable neutron source!!)

Part of neutron counting is to know every possible neutron detection system well. The detector, its efficiency and its sensitive volume is critical. The next issue is based on the innate noise and radiation immunity within the detector as this will determine the kind of counting environment for which it is best suited.

Low detection signal energies in a detector mean superlative shielding and robust pre-amplification, preferably, attached directly to the detector output with no intervening cabling. Following the pre-amp, short, shielded cabling must be used to connect with the pulse conditioning and counting electronics. Clamp-on, ferrite cable noise chokes can help limit shield-bounce in high noise environments, especially in longer cables.

In extremely high noise environments with well above "the floor" neutron fluence levels. A non-electronic detection method is far superior and very accurate. Bubble dosimeters and neutron sensitive films are preferred. The dosage readings, based on exposure times and calibration levels, can be back figured to average neutron fluence, and thereby, fusion rates in our case for the fusor.

In the end, if you would count neutrons, it is totally up to you to read and explore in some detail, neutron detectors and detection methods. It is not the kind of thing where one might go off and have a "quick dabble at it". It was the failing of many would-be great discoveries based on faulty neutron counting by those not familiar and competent in doing it in a scientific setting.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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