homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Kr85
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homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by Kr85 » Wed Nov 24, 2010 8:06 am

Hi all,
I'm new to radiation, as said in another thread, but own a good alfa particles scintillator (made in the former east-germany, bought as surplus but is working) and wanna know from experts if is possible to use it to made a simple neutron detector and wich kind of efficiency is possible to obtain from a thing like that.

I read somewhere that early neutron detectors were made using reactions between slow neutrons and light materials like aluminium or lithium or boron. That these materials have chance of capture a slow neutron and emit an alpha particle that could be detected by a sensitive scintillator.

Now, as said I already own a good and sensitive alpha scintillator based on ZnS(Ag) and covered with mylar window that can count single events, so single alpha particles that strike the scintillator and wanna try some easy experiment with that like putting a thin aluminium foil to cover probe head so that make impossible external alpha particles be detected but maybe sensitive to slow neutrons that strike the foil. The idea is that when a number of neutrons strike the kitchen aluminium foil that close probe window some of that will hit aluminium atoms and then these will release alpha particles then detected by the internal scintillator of the alpha probe.
Same for e.g. lithium or boron thin layers as cover window if I could get some and prepare the screen for probe head.

As moderator for fast neutrons I think I could make a paraffine/wax block or use some thick polypropylene block.

Now some questions:
1. Could this stuff work ?
2. Anyone already made something similar?
3. What could be efficiency of that thing detecting neutron fluxes ?
4. Which is the best material to try/use for the sensitive layer aluminium, lithium or boron ?

Of course I'm completely new to that business, have no neutron source of any kind and have no uranium minerals which could produce some spontaneous fission and give out some neutrons.

I'm mostly interested in principle of operation of that kind of probes and if I could detect some environment/natural neutron this way.

As always any hint and comments will be welcome

Best regards
Marco

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Richard Hull
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Re: homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by Richard Hull » Wed Nov 24, 2010 2:23 pm

Your quest is one of efficiency.

The average newbie, in his first pass at real fusion, will not make a lot of fusion, (neutrons). This means that to detect that all important first fusion, you need efficient detection.

The above method that you describe would have horrid efficiency and would require higher flux than you will first produce. This is the case with any method that encompasses slow neutron activation of materials. The materials you suggest have neutron cross sections that are just too low. Silver foil is one of the best.

There is a matter of statistics involved with low efficiency detection. Where do you start to rise out of the noise, statistically, that is associated with low flux operation common to the amateur effort?

The multiplicity of limitations here have been dealt with since the first neutron detection methods were worked out long ago, and by far brighter minds. The common methods of detection are the best, there are no real work-arounds for us amateurs, though there are routes to detection that are low cost. Most of these have been touched on and discussed here in this forum in the past.

Probably the best low flux solution is a hornyak button/scintillator detector that is carefully crafted. The cheapest activation scheme for low to moderate flux detection would be wrapping a 1B85 GM tube in silver foil next to the tube and then a thin lead foil layer over this and encasing it in a wax or polyethylene cylinder where about 1.5" thickness of moderator all around the GM tube is secured. This detects the beta radiation emitted from activated Ag108 and Ag110. All of these will be down in the noise until some decent isotropic neutron emission rate is achieved. (perhaps 20,000 n/s...Just a guess)

The 3He (helium3) tube remains the highest efficiency method of detecting very low flux levels of fast neutrons in moderator, but is currently far beyond the casual amateur's budget unless they fall into a rabbit hole where one is located inexpensively.

Oddly, the very folks who are doing a ton of fusion here are mostly equipped with 3He tube detection setups. These are folks who need these the least! Ain't it th' way.

Many suggestions are possible but they all involve either a lot of expense and or a lot of effort.

It is a matter of how many fusions you are producing each second, how efficient your detection scheme is and where the detection becomes real and rises out of the statistical noise floor.

Warranting that you are actually doing fusion before a critical audience is one of the most daunting tasks in this entire effort. In general, bubble detectors and neutron activation remain the least argued with and most fool proof methods of detection, but other methods that are clearly out of the noise are accepted as proof by those "in the know" here.

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.

John Futter
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Re: homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by John Futter » Wed Nov 24, 2010 6:31 pm

Marco
I have built a version of this see
viewtopic.php?f=13&t=6064&hilit=silver#p34508
not very sensitive but it works 0.3mrem of neutrons doubles the count from background
note in this i'm using much more silver to enhance the probability of silver being activated.

Kr85
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Re: homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by Kr85 » Wed Nov 24, 2010 7:10 pm

Hi
read both Richard's and your message and found truly interesting details about silver for this purpose of detecting neutrons once slowed down by a moderator.

Seems silver is really good for the purpose.

Both alternatives are possible to me using some efforts and finding relative materials, sure I can find a long thin walls GM tube to wrap with the foil, I have a couple of normal GM tubes (russians) but too small for the purpose; PMT/scintillator is a nice idea , I could find a spare PMT and try something similar too, probably is much more sensitive this way cause scintillator approach is usually more sensitive in detection of weak sources.
That's a cool idea for a neutron detector project. Thanks for linking that thread!

Best regards
Marco

Chris Trent
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Re: homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by Chris Trent » Thu Nov 25, 2010 7:47 am

According to the sources I've found, a 15cm thickness of plastic scintillator is between 20% and 30% efficient at detecting neutrons.

You've got to get quite a but of scintillation material to really make it work well, however it can certainly be more efficient than attempting to adapt a Geiger tube for the purpose.

In either case, the big problem for Fusor use will still be noise, either electrical noise from the fusor or power supply, or Xrays that will also trigger either the scintillator or geiger tube. Between the two, the scintillation counter is FAR more susceptible to noise.

In the end, you will have to make the determination which will work best for you in the conditions you are working in.


-Chris

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Re: homemade neutron detector using ZnS(Ag) scintillator, is that possible ?

Post by Starfire » Sat Nov 27, 2010 12:08 pm

All this has been discussed before - read old posts ;-

viewtopic.php?f=13&t=5432#p36433

And if you want to smile;-

viewtopic.php?f=13&t=5122#p33566

or search for 'Thomas Dressel' or BC-720

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