Anisotropic Neutron Emission - Discussion

[Richard Hull]

The issue of beam on target fusion in the fusor is real and can cause apparent hot spots, still isotropic, mind you, but appearing as multi-sourced neutron generators. (at the beam-wall junctures) I have noted before that coating a fusor interior with nickel, Titanium, or better still, paladium, would certainly dramatically impact the fusion numbers in a positive manner due to beam-on-target fusion adding to the far more mixed isotropic ion on ion gas collisons throughout the volume.

I have long posted many cold runs on Fusor IV here with full multi-run data that I positied were conditioning runs as in successive days, the runs got better and better as D was buried and remained hung in the walls when kept under vacuum between the frequent runs. SS and all metals suffer in a hydrogen environment and the energetic atoms will load into the crystalline matrix. (The very basis for the long suffering cold fusion work) Hydrogen embrillment is a very serious engineering issue in materials science and metallurgy, but for us, it is a boon.

I am actually undergoing this just now as I have run fusor IV for 12 runs over 12 days loading it up for the HEAS conference demo. The best run on day one was 42,000n/s, by the 4 th day's run, I was at 500,000 n/s and only last night hit 1.1mega n/s. This climb is not due to better vacuum or better techniques, but better wall loading I would warrant. This wall loading not only benefits beam-on-target fusion but also acts as a deuteron creation area at the wall via cook out and electron bombardment in the beam to enhance full energy deuteron arrival levels at the inner grid. (deuterons created at the ideal wall point) A double win.

As noted for some years here, the fusor operates on many levels that ARE doing fusion in many ways and places within it. It is so simple, the actual fusion methodology is complex and involves the entire volume and components.

In 1998 we noted that the fusor fused in the central grid star. By 2002 we had modified to the fact that it fused over the volume of the fusor and as early as 2006 we also added beam on target fusion. Our simple little fusor of 1998 got complicated and almost mystical in the number of fusion modality possibilities.

Chris got it right, I was commenting on the absurd idea of dipping a fusor in a bubble gel.

Richard Hull

[Monroe Lee King Jr]

Oh I see you actually want to insult me eh?

lol whatever

Monroe

I like the direct approach I don't have time to play the guessing game.

[Monroe Lee King Jr]

KJNW

Ahh indeed thank you for letting me in on whats going on. Yes, that does sound like a pretty quantifiable analysis method to me! Humm can you direct me to more information about the project? Interesting.

I still like the hard evidence bubble Dosimetry could provide. I don't see the polymer development being impossible to recreate. I suppose you could divide a tank in half that you could close around the fusor perhaps acrylic. I just like a direct visible method that could be much cheaper.

Monroe

I know they do it for MRI's and other imaging equipment not for neutrons but x-rays and such. So why not for neutrons?

[Carl Willis]

I'm glad the apparent confusion in this thread got sorted out.

To reiterate / summarize: When it's observed that the neutron field around a fusion apparatus is not symmetric, "anisotropy" (referring to the neutron-producing nuclear reaction) is very low on the list of explanations. According to the well-established measurements and theories pertaining to DD fusion, it's only really a plausible explanation in high-energy accelerator beam experiments, and most notably shows up when there are kinematic constraints on the product angle and energy distributions in some of the source reactions.

Likely causes for apparent neutron field asymmetry in hobby fusion projects are capture and scattering in surrounding materials, asymmetry in the source, inaccurate assumptions about the location of the source, and detector placement issues. All of these have just been competently discussed in this thread, and have been discussed previously. Jon Rosenstiel notably measured differences in the flux from a fusor that I was able to simulate through MCNP modeling of the stainless steel chamber.

Monroe: Carl's and his students' project has been discussed extensively in archived discussions and as soon as you get into those, you'll note he has a website as well. These existing resources should bring you up to speed on their project. I don't think anyone is out to insult you, but you've gotta realize that the credibility of some ideas--such as surrounding a fusor with a drop detector bath--can only be established through actual demonstration. I'm evidently not alone in doubting the practicality of this idea (for many reasons).

-Carl

[Monroe Lee King Jr]

Ok Carl well I'm not there yet. When I get to making neutrons and feel the need for the bubble dosimeter I will find out if it's feasible for me to test. If the polymer turns out to be able to be recreated cheaply I will try it myself. It was a hypothetical solution albeit one I like.

Monroe

Does it take time for the fusor to come to equilibrium before it produces neutrons or can it be pulsed? Held evacuated and then pulsed again? Or does it have to be hot all the time?

[JakeJHecla]

Just to clarify, as someone who had a hand in designing this set of experiments, the hypothesis behind the apparent anisotropy was that we were seeing beam-on-target fusion in the walls, and therefore the field doesn't look like what we would expect from a point source in the poissor. We never suggested or intended to suggest the neutrons emitted from the D(d,n) reaction had a preferred direction! As a next step, I feel that measuring the neutron flux using the fusor assembly with an AmBe (or other) neutron source held where the grid would (with the unit obviously off!) be would be helpful. It would rule out any shielding or reflection issues, as we know in this case that the neutron source can be modeled as a pointlike emitter. If we see deviations from a uniform field consistent with our previous results, it's an external condition and our previous data is an artifact of external conditions. If not, then back to searching for the culprit.

[Richard Hull]

No one has used a fusor successfully in pulse mode and reported back with a fusion "win". However, fusion should be very doable in pulsed mode.

Only a binned, calibrated, BTI bubble detector could be readily used in a manner that would be really acceptable at the amateur level here for quantitative work. The reason for this is that electronic counters would be very difficult to use due to their suseptability to EMP issues, pulse count separation, etc., and the difficulty in overcoming same in a credible manner. I have spoken of how a pulsed fusor might still use an electronic detection method in, now distant, past postings.

Pulsed work would have to be presented in a believable scenario with full voltage and current measurements in a time ordered manner, such as overlapping dual channel scope shots. It would be interesting work to poke around in, but most likely far less productive than a continuous run fusor, in amateur hands.

Current would lag voltage and significant, useful fusion would probably only be observed where the voltage was above 25kv, regardless of current. I would hope a 60kv peak voltage at discharge would be most successful. Richard Hester produced some interesting diagrams long ago using a hydrogen thyratron tube as the capacitor switch which is the desideratum due to its fast switch time, large current handling capability (1000's of amps) and ability to have a rather rapid duty cycle. (up to ~1000hz rate provided the joule rate capacity is not exceeded.) 60kv H2 thyratrons are very expensive. Custom spark gaps, while crude and limited could be fashioned by capable hands.

A more elegant and modern setup for pulsed work would involve IGBT switching of an H bridge into a custom oil bathed pulse transformer.

Richard Hull

[Richard Hester]

I was going to suggest a titanium vessel, but that would be prohibitively expensive and a perfect pain in the rear to fabricate. Coating the insides with Ti, as suggested earlier, is the easier route. Some bits and bobs from a Ti sublimation pump might be useful for such an attempt.

Later - I checked out the price of Ti Sublimation parts at Duniway, and boy are they expensive, even the replacement filaments. Seems they are a Mo-Ti alloy. Surplus/junk would be the way to go...