Fusor Running, No Neutron Detection

For posts specifically relating to fusor design, construction, and operation.
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Jim Kovalchick
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Re: Fusor Running, No Neutron Detection

Post by Jim Kovalchick » Mon Jan 27, 2020 8:08 am

I'm not convinced it's your counter. 2 to 4 mA at 25 to 30 kV is not necessarily a lot of fusion in a small cross fusor. My cross fusor started popping neutrons out at around 8 to 10 mA and above 30. The results were variable too with one day neutrons and next none. Have you tried different gas flow rates? If your chamber hasn't had a long heating period or is leaky, you may need to flow more d and not throttle your outlet as far closed.

Alan Sailer
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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Mon Jan 27, 2020 5:36 pm

Jim,

I'm not convinced either. I'm working on that.

As far as the higher current I'm worried that my much smaller grid will no take that amount of power.
I've got a small two loop tungsten grid. I was looking at one of your threads and the grid you are using is much bulkier.
Ti vs W as I remember.

Cheers.

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Mark Rowley
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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Mon Jan 27, 2020 6:23 pm

Jim,
Until I see pics of Alan's arrangement, his system seems to be very close to mine (minus the neutron detector). Using a 60kV precipitator, 2-2.5mA, 35mTorr D2, 35kV will make a respectable amount of neutrons. In my case ~300k n/s isotropic. BTI results, indium activation, and my Ludlum 2221 / SNM11 all support this output. At 20kV / 2mA Alan should be getting a very noticeable amount of counts over background.

Alan,
If the input and pressure readings are what you say they are, then you are 100% making neuts I contend there's no debate on this. Concerns over high amperage grid destruction is a non-concern. You will not need to go that high with your system.

As stated in an earlier thread, I'm not a fan of the Soviet 3He tubes as my experience as well as others show them to be much more tricky and suseptible to electrical noise than the boron counterparts (ie SNM14 or 11). I dont know why this is, perhaps something to do with the tubes pressure. And to reiterate, my previous attempts with the Soviet 3He tubes have all been with heavily shielded cabling, etc etc. Still no go. For detecting Po/Be neuts they worked great! This however is not the problem with Alan's system as he's not getting any reading at all.

Alan, if your picking up the 1-2cpm background count then I'm still somewhat in the gas integrity camp. Unless the background counts are some type of spurious noise there's no reason why you cant detect a higher number of neuts over what you can detect from background.

Mark Rowley
Last edited by Mark Rowley on Mon Jan 27, 2020 6:36 pm, edited 1 time in total.

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Mark Rowley
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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Mon Jan 27, 2020 6:28 pm

Alan,
If it helps, I can make a complete startup to fusion to shutdown sequence youtube video with my fusor to alleviate any concerns you may have about the required input power.
Let me know.

Mark Rowley

Alan Sailer
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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Mon Jan 27, 2020 7:31 pm

Mark,

Thanks for the information and offers. I am regrouping and considering options. Unlike Apollo 13, no lives are on the line and failure is always an option.

I have definitely been using your system as a model from the beginning. I'll try again to post a picture.

As you mentioned your issue with the He3 tubes was noise. As far as I understand the output of a He3 tube is lower than boron tubes. But with the scope
I am seeing clean pulses that fit neutron detection perfectly. One option that I hesitate to turn to would be shielding my scope so that I can eliminate
noise form the fusors and see if neutron production changes during operation. EMI shielding is painstaking though.

Back in the 80's when I was starting to work in engineering an older engineer told me that if you see it on a scope you can pretty much bet it's real.
With very few exception he was right.

Cheers.

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Mark Rowley
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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Mon Jan 27, 2020 7:44 pm

Alan,
Check out Dennis Brown’s posts in 2016/2017. He went through similar issues getting his detection system up and running. Not completely the same, but it should offer some insight.

Mark Rowley

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Richard Hull
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Re: Fusor Running, No Neutron Detection

Post by Richard Hull » Mon Jan 27, 2020 10:41 pm

A very sensitive charge amplifier is demanded on all 3He tubes as each pulse is just a whisper of current of a strength that should tickle an FET front end for sure. This is why Carl noted the electrometer which is easily capable of registering 10e-13 amp or lower currents. Many special FETs are quite capable of doing this as are a number of special FET operational amp ICs. Typically, in all proportional pre-amps in the nuclear biz, a single high impedance FET is the most commonly used front end component, due solely to the minuscule currents delivered.

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.

Alan Sailer
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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Mon Jan 27, 2020 10:47 pm

Mark,

I'll do that.

Richard,

I have considered rolling my own electronics for neutron detection. I just hadn't thought it would be needed.
Carl Willis's video showing a Ludlum 12/He3 detecting a moderated PoBe source was my model. It's why I bought
the 12.

Cheers.

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Richard Hull
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Re: Fusor Running, No Neutron Detection

Post by Richard Hull » Tue Jan 28, 2020 1:38 am

Believe me, If Carl Willis got the model 12 to work with his 3He tube, then you can too! It is a matter of having 1. real neutrons to count and 2. a known good 3He tube. Add a bit of skill in setting it up.

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.

Alan Sailer
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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Wed Jan 29, 2020 2:18 am

I finally got a successful photo attachment. I will be surprised if there is anything unusual.

The white cylinder is 30+ pounds of wax in a cardboard tube. A lexan tube is inside. An NM-188 He3 tube is inside that.
It is attached with a short BNC cable to a Ludlum 12 counter.

The grey box is a Convectron tube readout. The 2.75" cross is north of center. HV feedthru is to the right, viewport to the
left and D2 input top. Viewport seen by means of 45 deg front surface mirror. Additional shielding with 2 inch thick quartz window,
Plywood at top holds 1.5mm lead sheet forming radiation shadow. Vacuum pump (turbo-rough) under table holding the cross.

Precipitator supply hidden behind assembly along with HV meter (100Meg and uA meter). ~60kohm ballast. All wiring done
with 40kV silicone wire further insulated with plastic tube.

Th egrey box to the right has nothing to do with the set-up but is a homebuilt HV supply for a microflash unit. Positive output
or I would be using it for the fusor. It has a Variac like good HV supplies should have :-)

It's a very minimalist set-up.


DSC_0606.jpg

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