FAQ - How do we KNOW we are getting fusion neutrons

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Richard Hull
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FAQ - How do we KNOW we are getting fusion neutrons

Post by Richard Hull »

All that follows is written solely by Richard Hester in another forum, but is so good I make it into a FAQ.

The question revolves around proof of fusion neutrons (fast neutrons) from our D-D reaction. Richard's superlative summary is as follows........................

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At ~10^6 reactions/sec, no one will be seeing any measurable temperature rise or pressure rise from the fusion reactions.

In response to the original post, there is no doubt that there are fast neutrons coming out of the fusor, though, as they have been measured 6 ways by different researchers.

They have been measured using BF3 and He3 proportional counters, which detect neutrons very well, but cannot differentiate between fast and thermal neutrons.

They have also been detected using a Bicron BC-720 scintillator, which readily responds to fast neutrons via signals generated by proton recoil, but cannot see slow neutrons well at all, except perhaps to an extremely small extent via the capture gamma ray that occurs when a proton absorbs a fast neutron that has been slowed almost to a stand still due to elastic collisions inside the detector. Since the scintillator is designed specifiically to have only a low-level response to gamma radiation, this contribution will be extremely minor, especially since the discriminator in a detector system using this scintillator is deliberately set high to reject low level output pulses that can result from gamma excitation, PMT noise, etc.

Fast neutrons have been indirectly observed by one researcher back in 1999 using a diffusion cloud chamber via the recoil protons generated by collision with hydrogen nuclei in the alcohol vapor inside the chamber.

Fast neutrons have been detected using a plastic scintillator, which has a good detection efficiency for fast neutrons via recoil protons generated inside the scintillator by elastic collisions between fast neutrons and hydrogen nuclei in the scintillator host plastic.

Two researchers here have also observed unmistakable signs of neutron activation in Indium and Manganese by using a moderator between the operating fusor and the sample being irradiated. In each case, the activated element was identified via its characteristic gamma spectrum using a multichannel analyzer. Activation can also be used to distinguish whether low or high energy neutrons are emitted from the fusor, as activation for Indium and Manganese only occurs due to thermal neutrons. Removing the moderator between the fusor and test sample stops activation, proving that the neutrons coming out of the fusor are relatively high energy.

More recently, fast neutrons have been detected by two researchers here using a bubble detector, which only respons to fast neutron flux.

Researchers at the University of Wisconsin have also detected the fast protons from the alternate branch of the D-D reaction using a silicon PIPS detector. The observed energy correlates closely with the expected proton energy resulting from the D-D reaction.

So - we know for sure that neutrons are coming out of the fusor, and fast neutrons at that. They occur at applied potentials of as low as 10kV, ruling out such exotic reactions as stripping, which starts occurring at a threshold energy of several Mev. The reaction cross-section for D-D fusion has been extensively documented all the way down to 10kev and below, so we know that there is reaction down at those energies, even though the cross-section is small. No other neutron-producing D-D reaction of any sort has been documented for low incident energies. Fusion is being done, even though the reaction rate is miserably small compared to the input power.

Richard Hester
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ - How do we KNOW we are getting fusion neutrons

Post by Jon Rosenstiel »

Six ways if one counts neutron activation. (Reported here by at least two researchers).

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Re: FAQ - How do we KNOW we are getting fusion neutrons

Post by Richard Hester »

I will go ahead and add that to my original post, and Richard Hull can then revamp the Faq if he likes I'd thought of it, but didn't stick it in at the time.. Activation is definitely proof that there are neutrons coming out (just like with the BF3 and He3 detectors), but not an unambiguous proof of fusion to the nay-sayers, as the activation is caused by thermal neutrons. The tests that point to fast neutrons are the most indicative of fusion. A BF3 detector backed with a bubble detector or fast neutron scintillator would be a pretty good 1-2 punch, for example.
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Re: FAQ - How do we KNOW we are getting fusion neutrons

Post by Richard Hull »

I will revamp as needed. Can't believe we missed the best, plus-ultra indicator of neuts.

I figure that Neutron activation is the king of indicators, but requires a really kickin' system to herald evidence of Neutron production. Still it is the BEST of the best neutron indicators with the BTI bubble detector behind that and the He3 detector in third place. In fourth place I would put it at a tie between the BF3 and a very well made Neutron Scintillator system using a Bicron neutron Scintillator or its equivalent. Fifth place would be the cloud chamber recoil detection scheme.

I figure, though, that 100% of us folks looking to detect the presence of neutrons are near the bleeding edge of production and neutron activation just is not where we are at the moment. This makes neutron activation probably the LAST indicator of neutrons they will ever use.

The overall winner in number one place for me, given only a low to moderate fusion output would, of course, be the BTI bubble detector, based on cost and zero error and noise factor in use.

The most sensitive indicator would be a large HE3 tube in a water moderator jammed against a fusor. I get an immediate, uncontestable neutron signature in mine at 10kv. One would have to operate a fusor for an hour or more to see this in a bubble detector.

Want ultra low end sensititvity? Operate a He3 system.
Want easy, cheap, zero noise detection? Use a bubble detector

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ - How do we KNOW we are getting fusion neutrons

Post by Richard Hester »

Done...
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Re: FAQ - How do we KNOW we are getting fusion neutrons

Post by Richard Hull »

updated

RH
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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