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FAQ - Surplus portable neutron detectors

Posted: Tue Jul 10, 2012 2:28 pm
by Richard Hull
Many are in search of neutron detectors. Once common on e-bay, the units have been gobbled up to such a degree that they are very rare now. The most common to find are the old Eberline units with the PNC-1 leading the pack. On rare occasions, a rem ball, (Bonner sphere), with a mated PNR-4 will be encountered.

In most all instances, the seller will have no idea as to whether the thing works or not and admits it, saying "All sales final". In spite of this warning, prices usually climb quickly to far more than such a "pig in a poke" is worth. Such seems to be the desire to possess neutron counters. I often wonder if this "frenzy" is fusioneer driven since prior to the fusion effort, such items were often encountered and sold rather inexpensively. Most of this ended by 2006.

Speaking from experience and having purchased several of these since 1999, if they are surplus they are probably dead unless the seller warrants a fully functional unit.
Common issues are grossly corroded battery case, failed HV supply, or defective tunnel diode, (PNC-1, irreplacable). The PNR-4 has a special log-log dual movement meter and is often defective or damaged. (I have two of these that are parts-only units.)

Victoreen and later, Nuclear Associates, made the large black moderator "snoopy" style counters. These are also found at a functional level of only ~20%.

Most all survey type portable counters require a strong neutron field to push their needles up scale, if all is in good order. The tubes are typically a rather tiny Nancy Woods BF3 tube and the resultant sensitivity is low even with the counter in contact with typical amateur level sources.

The best use for these counters is with their audio outputs being be fed to a digital counter where good data over longer periods of time can be collected and recorded.

Using one of the above, a decent count rate can be obtained at about 150,000 neutrons per second. (isotropic). Valuable data counting can begin at about 50,000 n/s with easy detection at about 10,000 n/s. This last figure is about where the amateur will first start to fuse unless he is very lucky, indeed. As skills and fusor conditioning improves the amateur can only then really see much benefit in the survey meter type neutron detector.

Of all the old meters to have, the PNC-1 is probably the most useful if in good order. It allows for close contact with the fusor or source and is nicely portable and uses common D cells. I have one that had the battery holder and compartment ruined and have wired two leads coming out to go to a simple bench supply instead of batteries.

A rem ball, by itself, can be very useful if the tube is good. Good electronics for the Bonner Sphere can be assembled either from standard NIM components or, better still, modern electronics cobbled up by adroit hands using some of Richard Hester's excellent circuits posted in these forums.

Any of these items offered on e-bay or surplus need to be looked at with a jaundiced eyed. In unknown condition, a PNC-1, if complete, is worth about $200.00 max
If warranted with a money back agreement and stated to be working and tested, then $400.00 - $1,000 would be acceptable.

A naked, (no detector) PNR-4 is not worth $100.00. However if it is with a remball and is functionally warranted, then $1000.00 would be a modern normal maximum. A naked remball that has the tube in it and is warranted is worth at least $400.00 or more.

A Snoopy, if warranted, is worth $500.00 to $800.00 if unwarranted and complete it might be worth $200.00-$400.00.

Extremely old portable neutron counters should never be considered as they are often vacuum tube based and use batteries that can no longer be purchased or use some sort of scintillation detection that is very low in efficiency. Such older units were made for very high neutron flux fields. These are of curio-antique value only.

Finally, you may see tiny modern electronic handheld counters that tout that they can detect neutorns. Well, Maybe, but they are not worth the time to consider as they will only detect large neutron field levels as well.

Be advised that many of the above mentioned and recommended Eberline units have sold in the distant past for far less than the above quoted figures and could be sold in future for less, as well. However, many insane bids have been placed that have pushed even un-warranted items into ridiculousville! Buyer beware.

Often, the best overall solution and obtained at the lowest cost, is to purchase a good neutron detector tube, (still can be costly), and build or assemble your own moderator and electronics. (what I did with fusor IV) But, this FAQ was about surplus, all-in-one counters and I will leave it here.

Richard Hull

Re: FAQ - Surplus portable neutron detectors

Posted: Tue Jul 10, 2012 5:27 pm
by Chris Bradley
Richard Hull wrote:
> Finally, you may see tiny modern electronic handheld counters that tout that they can detect neutorns. Well, Maybe, but they are not worth the time to consider as they will only detect large neutron field levels as well.

For info; the PoliMaster series of pagers (such as the PM-1703GN - note, 'GN' shows it has the LiI/Eu scintillator in it - the plain 'G' just detects gammas), which are re-branded under various names [e.g. see Frank's: viewtopic.php?f=13&t=5870#p34314 ] are listed in the spec sheet as being usefully sensitive to thermal neutrons. So I presume they can also be used with a moderator, which should then increase their sensitivity to an adequate level.

Thermal neutron sensitivity is listed in their specification as increasing their sensitivity to 1.3 cm^2/neut.

This, for example, would be equivalent to a count rate of ~10cps at 10 cm from a source of 10,000 neutrons/s (background reading is usually zero at all times, at ~sea level).

Just detecting fast neutrons, it'd need (according to the data sheet) ~250,000 neutrons/s at 10 cm for a count indication of 10cps.

One might also need to remember, however, the possibilities of electrical interference that may swamp the signal of any small device. This may have been as Frank's demonstration.

Re: FAQ - Surplus portable neutron detectors

Posted: Wed Jul 11, 2012 3:08 am
by Steven Sesselmann

While the traditional neutron detectors are becoming hard to find, there has been a surge in the availability of Russian tubes. Fairly big B10 tubes can be bought cheaply, but some knowledge of electronics is needed to make use of them, most of it has been covered here in previous posts. ... rch=Search

No association with seller....


Re: FAQ - Surplus portable neutron detectors

Posted: Wed Jul 11, 2012 2:13 pm
by Richard Hull
Chris, what is the normal cost on one of these? Most folks don't have more than about $500.00 to put into a neutron counter. A few ultra serious folks might have $1,000.00 to devote to the effort.

I went to the old posting and I remember this device. Frank brought it to the HEAS and I was under-impressed with the neutron measuring capability. It was indeed cool in many ways, but as I remember, Frank got a super good deal on a used one and the new list price is over $4,000! I may be sketchy on this price.

Steven, I noted in the FAQ that the best and cheapest solution might be to purchase a naked detector tube and move on from there with your own electronics. The recent glut of Russian tubes might be a God-send for those willing to work up their own electronics.

Richard Hull

Re: FAQ - Surplus portable neutron detectors

Posted: Wed Jul 11, 2012 5:41 pm
by Chris Bradley
No disagreement with you there, Richard. Last I heard they were around the Euro 2,500 mark new. But how much is a new 3He tube? For sure, these things cost megabucks (well, kilobucks at least!) when brand new and warrantied. But we keep out eyes out for good 2nd hand deals, and PoliMaster pagers have come up on ebay and elsewhere at affordable levels already. I guess they are rarer 2nd hand buys simply because they've not been produced for as long as the other options you mentioned.

But bear in mind that today will be the history of the future. Some day, someone will read this thread and think "Ah - I saw a PoliMaster pager last year, in 2040. It must've been 50 years old. It was only $20,000 - just a week's salary ! Glad these ancient forums still have FAQs on this vintage stuff!"

However, for now they remain relatively 'untested' in regards the normal 'sequence' of stages in an amateur fusion effort. How best to use such devices, and whether they can adequately perform in the 'fusor' setting, will be determined in the long-run by folks getting hold of some, trying them, and figuring out 'best practice' to get them to give a trustworthy count - if they can.

Re: FAQ - Surplus portable neutron detectors

Posted: Fri Jul 13, 2012 5:14 pm
by Frank Sanns
The FAQ give the text but here are some photos. These are a sample of my neutron detectors and He3 tubes.

Clockwise in an Archimedes Spiral (sort of) starting in front:

22" x 1" He3 tube without the moderator
Thermo Interceptor CZT based MCA with He3 tube
6" x 1/2" He3 in moderator
Neutron RAE gamma scintillator with Li6 neutron scintillator
Ludlum 12-4 BF3 REM Ball
PM 1401GN gamma scintillator with He3 tube

Frank Sanns