Does PB11 produce neutrinos?

[kunkmiester]

Like the title said. One theory I've seen in detecting a fusion reactor running DT is neutrinos. Would a polywell be pumping out anything of the sort?

[Art Carlson]

Like the title said. One theory I've seen in detecting a fusion reactor running DT is neutrinos. Would a polywell be pumping out anything of the sort?

It sounds like you are confusing neutrinos with neutrons. D-T produces copious neutrons. p-B11, in its simplest form, still produces neutrons, but 1000 times less. Under special conditions, this could be reduced still farther. (The probably insurmountable difficulty with p-B11 is producing net energy.)

Neutrinos are produced by fusion reactions in stars, but not in the laboratory. The reason is that neutrinos are associated with the weak nuclear force, which is, well, weak. The cross sections of all such reactions are too small to be of interest for terrestrial energy production.

[chrismb]

Like the title said. One theory I've seen in detecting a fusion reactor running DT is neutrinos. Would a polywell be pumping out anything of the sort?

In a word, no.

Maybe you're thinking of neutrons.

Neutrinos are almost undetectable anyway, very small interaction with matter. There are a few detectors in the world, generally a huge volume of water surrounded by scintillation detectors.

There are 3 'types' of fusion reactions dependent on the nuclear forces that mediate that reaction; strong, electromagnetic and weak.

All of the reactions that are considered for producing fusion energy are mediated by the strong reaction. This is because all the energy comes out as the kinetic energy of particles. It is the excited fusion-nucleus product shrugging off the excess energy by breaking up.

The electromagnetic reactions are typically where the nucleus stays in one piece and pushes out the excess energy by releasing photons, which would be high gammas in that energy range.

An example of the above two would be D+D which goes either to p+T or n+3He for almost all of the time, but 1 in 26,000 reactions end up in it giving out a huge 23MeV photon (pair?).

To get neutrinos, you need the last reaction type; a weak mediated force. If a proton breaks up into a neutron and a e+ then there is an excess binding energy not accounted for. That excess energy manifests itself as a neutrino.

In terms of 'typical probabilities', if you like, a strong nuclear reaction (viz. releases neutrons, alphas, etc.) is about 4 orders of magnitude more likely than an electromagnetic reaction, which in turn is about 18 orders of magnitude more likely than a weak reaction.

You may also find a neutrino-emitting isotope is formed after an electro-magentically mediated reaction. If the nucleus 'survives' the fusion event and releases photons, it may be an unstable isotope. e.g. p+12C->13N+hv. The 13N is unstable and decays by the weak force, releasing a e+ and a neutrino, which effectively converts one proton into a neutron, thus leaving 13C.

[Nik]

IIRC, there are some rare nuclear isotopes which *may* have a seasonal modulation superimposed on their decay rate.

( There's only a few with half-life in potentially sensitive range, the data rate is very low, the sources of error and interference multiple etc etc

Very, very tentatively attributed to solar neutrino flux and Earth's mildly elliptical orbit.

Jury's still out on this one !!

[icarus]

Or it because Eddy's in the space-time continuum ....



(who the hell's Eddy and what's he doing in there anyhow?!) oldie but a goodie.

[rcain]

how about low temperature phyics. i think things change a little yes?

[kunkmiester]

Interesting to know. I suppose then, a more compact neutrino detector would be quite useless, save for an alternative using a synthetic gravitic field rather than magnetic to contain plasma.

[D Tibbets]

If the decay rate can be controlled with devices at our disposal, it would very dangerous.. Imagine just fissioning just a gram of natural uranium at a time. Or boil steam from Sr-90 going superluminant with gamma output.

The head hurt I get on how they predict that not all the atoms in a sample decided whether to decay, or not to determine the half life in simulation is horrible. Somehow do the particles know when their neighbor is decaying and influence holding off their own event? Or is it the decay that produces more in the sample at a specified time that we can't determine? Or is it just chance that a 2kg rod of plutonium does just 100% spontaneously fission and we haven't seen the roulette wheel stop on that chance yet?
How about those sub critical cores in the stored nuclear weapons, are they really safe? Is that why they need continued testing and verification against an accident such as that?


Half-Life? Or is it an effect from something outside of the sample encountering? ripples in the fabric of the universe? Who knows.

It is all statistics. Something is statisticlly likely to occur within a certain time frame. An isototope may have a 50% chance of decaying after a certain amount of time. It may also decay at shorter or longer time scales, but these events are less likely. So the distribution of possible decay events is a bell curve with the most likely time the peak of the curve. This works well for predictions when you have a large population, not so well with small populations. If a mass extintion asteroid hits the Earth on average every 100,000,000 years, that tells you that the event is rare, but it does not preclude an asteroid strike next year. Now, if you were talking about a few million planets in the same situation, the repeatable accuracy of the prediction goes up. A proton is predicted to decay at extreamly long time frames (100 billion years?- some of the tests have been running long enough to put pressure on the prediction- if none are detected in the next few years, they may need to rethink the theory, or the experement), Despite this prediction, statistically, there is a not quite infinitly small probability that they could all go off at once.
It is all a matter of chance.

Dan Tibbets

[TallDave]

And this is Eddie's couch, then?

[D Tibbets]

Interesting to know. I suppose then, a more compact neutrino detector would be quite useless, save for an alternative using a synthetic gravitic field rather than magnetic to contain plasma.

Yes and no- If you are seeking to detect certain types of fusion like that in the Sun, neutrinos can be a marker. But, the sensitivity of the detector is extreamly tiny. Neutron detectors have a sensitivity such that they pick up ~ 1 neutron out of a thousand that are passing through it (if the background noise can be controlled well). A neutrino detector will catch perhaps 1 neutrino out of the trillions upon trillions of neutrinos passing through it. They work because they are made large (millions of gallons of ultrapure water or dry cleaning fluid) and the noise (mostly cosmic rays) is kept very low by burying the detectors thousands of feet underground. Even then they only detect ~one neutrino per week (?), despite the stupendus numbers of neutrinos passing through the Earth from the Sun, or occasionally a super stupendous amount of neutrinos from a distant event like a supernova.
I may not be remembering quite acuratly, but a ball park idea of how difficult it is to detect a single neutrino is that you have to have a sheet of lead 10 light years thick (that would be ~ 60 trillion miles) to have a 50% chance of the neutrino interacting with it.


Dan Tibbets