Power Supply for a Boron based Russian Neutron detector

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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Dennis P Brown
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Power Supply for a Boron based Russian Neutron detector

Post by Dennis P Brown » Tue Jan 03, 2017 2:57 pm

I built a variable DC power supply that covers 0.5 to 3 kV at a few micro to maybe a milli-amp (a small DC to AC high voltage converter.) The whole device is battery powered and also provides a 2-5 amp 12 volt power source for a DC-AC converter that provides just 120 AC voltage to my counter system (the whole point of this supply is to isolate all the detector systems from the monster 32 kV, 100 milliamp power supply. That really big PS feeds the fusor and is both on my line voltage for the house and is star grounded to all other devices (resulting in ground loop issues for the detector when it was hooked to the power grid.))

While my detector/counter system is now fully isolated (and partly shielded) I discovered that the very high frequency tiny x-former in my battery supply drives my counter - it thinks the voltage swings are just breakdowns in the detector tube ... . No idea how to counter that effect via simple electronics - a choke might help but I have no idea how to implement that approach - any ideas on that approach would be helpful.

In any case, I am thinking that a brute force approach might solve the issue; that is, I should bias the detector tube's outer casing (it is buried in an insulating case of wax to moderate the hot neutrons) and hook the counter up to the detector's input connector (or the reverse if I think the counter would offer a good ground path ... .) My thinking is that the counter circuit will then never see the high frequency power supply since it will be insulated by the very low pressure gas in the counter tube; that is, until a neutron creates a "break down" spark. Then that transient will be counted but then cease as the spark quickly dissipates.

Of course, as I have learned over and over, 'good' ideas for work around with electronic problems are often really terrible ideas that one's ignorance of proper electronics often gets the person (me) into trouble and failure - again, any input would be highly appreciated!

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Richard Hull
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Richard Hull » Wed Jan 04, 2017 5:32 am

Neutron counters are proportional, therefore, The bias supply should be as quiet, (zero ripple), as possible. Only scoping the supply output can tell what is going on. This is where a good voltage divider will come in handy. Put the scope on its highest range 50 or 100v/div and AC volts on the input selector and turn the bias up to only about 300 volts, that will not overdrive the input capacitor and see what you have in the way of ripple. You just can't have any ripple. You better see a straight line........ A CCFL supply is great for GM work but absolutely un-acceptable for PMT or especially proportional detectors.

I assume you just rectified and attempted to filter the DC to HV AC supply's output. I guess it could be done with a good scope and a lot of cut and try filtering. High frequency supplies are great but a good hand is needed to stiffle the HF ripple.

I have been fortunate to get a professional ultra-stable bias supply for my 3H3 neutron counter. I still use a good old vacuum tube, (glow FET), HV 60hz supply with decade precision voltage knobs for my PMT gamma spec.

Richard Hull
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Jerry Biehler » Wed Jan 04, 2017 6:56 am

Ultravolt makes some very nice variable high voltage supplies. Very clean output with very little ripple. I think this is a 4kv negative out supply: http://www.ebay.com/itm/ULTRAVOLT-2A12- ... SwdIFXy73P

They are often used for HV bias in SEMs and PMT supplies.

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Rich Feldman
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Rich Feldman » Wed Jan 04, 2017 3:12 pm

For measuring ripple voltage with a 'scope, don't overlook the details Richard gave about AC coupling.

If your DC blocking capacitor is external, with appropriate voltage rating, then you can run at full HV and go to 'scope input without attenuation. Still need to consider four-digit voltage spike at scope, from initial charging of capacitor. External protective clamp diodes, or perhaps a neon glow lamp, can take care of that.

Glad to have seen warnings at the forum about ripple voltage, before connecting my own BF3 tube to anything.
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Richard Hull
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Richard Hull » Wed Jan 04, 2017 5:08 pm

You really won't hurt a BF3, 3He or boron lined tube with even huge amounts of ripple. However, it will really mess up your counting with false counts. In rare cases with a good preamp and discriminator where the signal output level is higher than the ripple. (rare), you might be able to discriminate out the noise. It is always better to eliminate all the ripple at its source though. The rule is, don't put noise into a preamp.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Dennis P Brown
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Dennis P Brown » Fri Jan 06, 2017 3:21 pm

Once again, every single part of a fusor is a major project in of itself unless one just buy's finished, turn key stuff ...lol. (We are lucky Steve has that turn key detector system. Yes, that is on my list to get but I am stubborn and will first exhaust all other avenues (and myself, lol) first.)

So, to just cover the start of a fusor project I have built a full fusor power supply from nearly scratch (100 ma pulse, 60 ma continuous @ 32 kV), check; complete gas D2 supply, check. Fursor body with all feed thru's/connectors, check; vacuum system, check; various vac gauges, check; and fusor power cables, check; radiation shielding/detection, check. Now that I have a detector tube and an advanced counter, my power supply for the detector tube is my new project ...lol.

I am, getting a lot of experience and knowledge of many, many projects; everything from practical high vacuum systems (assembly, operation issues), various high voltage systems (pulsed and continuous for both AC and DC w/related theory), low voltage supplies, detectors and their theory, machine work (vacuum connectors, feed thru's, o-rings etc), leak detection techniques, battery supplies, electro-statics, van de graafs, high voltage metering, ground loops, ground systems, x-former theory and of course, operation of a fusor (which is a rather interesting subject that one gets to address when they think they have everything done - not!)...well, enough said of that phase.

I now realize that even if I never prove fusion I have learned far and away more than I ever thought I would relative to a lot of interesting subjects - yet I am simply amazed at how talented so many here are and in so many area's here;also the amazing breath and depth of knowledge at this site is just a wonder!

Well, I will carry on and see if I can over come this last issue. Have to say, frustrating on a number of levels but also, many of my side projects have been very satisfrying both in doing and understanding so, in general, has really been a lot of fun.

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Re: Power Supply for a Boron based Russian Neutron detector

Post by Jeroen Vriesman » Wed Jan 11, 2017 10:23 am

One very cheap and simple way to make a counter tube supply is:

a) buy an electric flyswatter (about 4 euro's)
b) take out the electronics, and measure the polarity (the wire colours were all wrong...)

you now have a 1200V power supply, usually 3V input, in my case the output was floating, but I connected the (-) output to ground.
On the HV side I made a voltage divider with some 4M7 resistors and a 0.22uF capacitor, this filters out all ripples and gives a stable 400V.

Next: connect the anode of the tube to the +400V through another 4M7 resistor, and the cathode to the base of any simple NPN transistor, emitter to ground, and a small 60 ohm speaker between the collector and the +3V

Besides the flyswatter everything is "salvaged", so without the tube this is a "4 euro Geiger counter".

https://youtu.be/qJK3cFFGSvg

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Richard Hull
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Richard Hull » Wed Jan 11, 2017 6:57 pm

If the above info works for you then go for it. Those fly satters are sold at every Harbor Freight store and during the summer are often offered on coupons for free! I used one to make a static grass application supply for my HOn3 train layout. Lots of neat dual purpose and re-purposable stuff out there.

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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Steven Sesselmann
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Steven Sesselmann » Wed Jan 11, 2017 8:37 pm

Dennis,

I don't think you mentioned which tube it was, but be careful not to run it higher than the recommended voltage. Some of these tubes like the SNM-12 only need 450V and if you go higher than about 500V you have a geiger counter instead of a neutron counter.

The other thing to note with the corona counters is that they work in a continuous discharge mode which makes the output very noisy, and due to the low efficiency of these tubes you only catch a pulse every 10 minutes or so. The pulse is statistically above the noise but not by much, blink and you miss it.

Note, these tubes need high value load resistors in the order of 100 M Ohm.

Without a good oscilloscope it would be almost impossible to get one of these tubes working.

If you need a preamp for the Russian tubes I sell them on my web site.

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
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Re: Power Supply for a Boron based Russian Neutron detector

Post by Grigory_Heaton » Thu Jan 12, 2017 12:36 am

That flyswatter Geiger tube supply is very interesting, I think I'm going to order one and try it out for myself. Thanks for the tip! Have you tried it with one of the surplus cheap neutron tubes (B10 or He3) on Ebay? I feel like it probably wouldn't work at detecting solely neutrons given the issues that others in this thread have pointed out but it could be worth a shot if you already have one of those tubes.

I've had some success using a disposable camera flash circuit (modified so that it just provides 600V DC off of 2 AA batteries without the storage capacitor or flash tube involved) to drive a surplus Soviet SI-3BG tube ($5 on Ebay). It is able to reliably detect 1 uCi Americium buttons and "Negative Ion" scam Thorium-containing stickers but the tick count is really low, far lower than my CDV-700. I think this is due to the tube itself being built for very high radiation environments, not the power supply, so perhaps another slightly more expensive Ebay geiger tube would provide better results.

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