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Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Jan 07, 2018 12:55 am
by Jim Kovalchick
-38 kV, 8 mA, 6 millitorr

I'm convinced my neutron indication is the issue. Our PNC-1 is on the blink, but I think I can connect its BF3 tube to a scaler.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Jan 07, 2018 4:25 pm
by Richard Hull
That is a little Nancy Woods tube, but BF3 is a the best detector of neutrons after the 3He tube of the same size. The PNC-1 uses a good paraffin moderator. Good luck.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Jan 07, 2018 5:40 pm
by Jim Kovalchick
This morning I finally confirmed neutrons from this latest fusor. I used the BF3 from our PNC-1 and the standard PNC cad covered parafin block moderator, but connected to an old Ludlum 2200. At 38 kV, 8 mA, and 5.9 mtorr I measured 300 cpm well over a foot from the fusor center. The moderator pull test passed with flying colors because the bare tube placed directed on the shell of the chamber went down to near zero cpm. The ultimate proof was activation of a thin piece of silver solder to 40 percent over background. Im sure I will get better activation numbers in future runs with better material and geometry.

My estimate of neutron production is rough at best, but right now I think at least 750,000 per minute. The same tube measured 400 cpm on Richards fusor running at a million a few years ago at a HEAS. I could get closer to Richard's poisser, but the electronics are different this time.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Jan 08, 2018 1:44 am
by Jim Kovalchick
An evening run of my fusor at 39 kV and 8.5 mA yielded 400 cpm on my BF3 tube. Given the distance from the chamber and comparison reading of the same tube at Richard's I am estimating that my fusor has passed the 1 million neutron mark.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Jan 08, 2018 2:35 pm
by Richard Hull
Great work!

The little BF3 tube did yeoman duty once hooked to the Ludlum. I have stored away in my lab, somewhere, a rather large BF3 tube that I bought in the late 90's from Don Orie of O.E. Technologies when he offered an attractive little box of assorted color quarks in his printed catalog. We all miss Don's surplus mecca. To my knowledge he was the only source of fully warranted surplus neutron detection tubes. With e-bay it is always a pig in a poke.

This big BF3 tube is about 2.5-inches in diameter and well over 2 feet long! I obtained my 3He tube so soon after the BF3 that I just tucked it away. (somewhere...Or I might have even sold it at a long ago HEAS gathering and forgot).

Continued best wishes on what will surely be improved operation. I am sure you can hit the two mega mark in future.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Jan 08, 2018 3:54 pm
by Jim Kovalchick
Thanks Richard. At this point achieving big numbers isnt among my primary goals, but they will help. I am particularly interested in doing some activation and fiddling with alternate neutron detection methods.

Next steps - not necessarily in order of priority
1. Shielding - I am at the point where the xrays are disfunctional and will become hazardous. I will be looking into some shielding that will make my lab safe without limiting easy access to controls. I believe my xrf, feedthrough, and chamber can do some more volts if I add the right amount of lead. I also believe that good shielding is much better than electronic discrimination when it comes to sorting neutrons from photons.
2. Improve my installed neutron indication. The geometry and thermalization I'm using are not optimal.
3. Improve the dimensions and geometry of my neutron oven.
4. Spend a little less time in the lab and more with my spouse. The holiday push to the mega mark caused some understandable grumbling.
5. Improve my gas control. I am currently using an old variable leak valve that experienced some corrosion in a former life. It has beautiful fine control except there is a spot in its span that seems to pass extra flow causing me to juggle both it and the main vacuum valve as I pass through it.
6. Rebuild the grid. I have managed to avoid sputtering my tungsten all over the chamber, but I'm afraid I wont always be so lucky if I stick with my current conductor. I have procured some stranded tungsten from the orphan bin at tungsten.com for this purpose.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Jan 21, 2018 12:22 am
by Jim Kovalchick
I was able to fix my variable leak valve. Turns out that if the screw drive is slightly misaligned it can momentarily reverse act. A simple adjustment fixed the issue.

Now that I have smoother gas control to walk up my voltage I toyed with some longer 40 kV operation. Tonight I sandwiched a one ounce silver coin in some hdpe and stuck it next to of the base of my chamber for about 10 minutes at 40 kV and 8 mA. After shutting off the power and closing the gas, the coin still was more than three times background on a pancake Geiger. This makes me happy.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Sun Jan 21, 2018 4:41 am
by Richard Hull
That kind of activation is typical of what I get at 750,000 n/s + +. You are fusing big time! More, from this point, will be easy.

Richard Hull

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Jan 29, 2018 12:01 am
by Jim Kovalchick
My current grid gets a little thermionically unstable at the high end of my operating range. I would like a little more current and voltage so I am pondering a new grid. I haven't installed it yet, but this one uses heavy braided tungsten instead of single strand. This also only has two loops because the heavy nature of it makes my crimp construction more than awkward. Opinions welcome.

Re: Wait, what? Tiny fusors? Not for me!

Posted: Mon Jan 29, 2018 5:36 am
by Richard Hull
I have used a simple two loop tungsten grid for 4 years. It looks like your grid in the photo. We all know I can and have done good work with this simple grid. A complex geodesic sphere looks really nice and gives off many star rays, but I doubt it will do much better than a well done two loop grid.

Richard Hull