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Weller and his colleagues took a fresh look at the hydrogen-boron reaction at the Triangle Universities Nuclear Laboratory (TUNL) on Duke’s campus. They expected to confirm the accepted wisdom that a collision of one hydrogen particle and one boron-11 particle produces a single high-energy alpha particle -- which produces electricity well – and two lower energy alphas, which are less useful for generating electricity.
Instead, the team found the collision yields two high-energy alphas, which shoot off at an angle of 155 degrees, along with one lower-energy alpha. The existence of this second high-energy alpha could mean these kinds of fusion systems are able to produce much more electricity than expected, says Duke nuclear physicist and study co-author Mohammad Ahmed. The results appear online in Physics Letters B.
The unexpected finding appears to confirm a long-forgotten observation from physicists at Cavendish Laboratory in Cambridge, England. In 1936, they made crude, but apparently correct, estimates of the two higher-energy alphas.
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excerpted from an article at physorg
P-B11 has 2 high energy alphas, not 1
Here is the paper:
http://research.duke.edu/sites/default/ ... -paper.pdf
Finally something interesting going on.
http://research.duke.edu/sites/default/ ... -paper.pdf
Finally something interesting going on.
I can read the words they wrote in the paper, but I don't see in their results the evidence for their conclusions. I guess it means I'm just a bit thick.
I was of the understanding that the secondary 8Be aa break up leads to a random distribution of directions and energies (depending on the angles of the disintegration particles of the 8Be relative to the original 8Be track) and that this is not inconsistent with the energy distributions seen, e.g.; as per; viewtopic.php?p=13981#13981 . I guess this Belyaev paper suggests there are things still unexplained.
Can someone please explain to me how the data in the Phys Let B paper leads to the results they claim? Maybe there's more to it.
I was of the understanding that the secondary 8Be aa break up leads to a random distribution of directions and energies (depending on the angles of the disintegration particles of the 8Be relative to the original 8Be track) and that this is not inconsistent with the energy distributions seen, e.g.; as per; viewtopic.php?p=13981#13981 . I guess this Belyaev paper suggests there are things still unexplained.
Can someone please explain to me how the data in the Phys Let B paper leads to the results they claim? Maybe there's more to it.
Could someone also explain what they say with "Our results also will have a pronounced impact on the design of a possible aneutronic fusion reactor."crj11 wrote:It is interesting that the work was partly sponsored by Tri Alpha Energy
Why? This is a completely unexplained statement. What difference will it make? The first task is to get the damned p and 11B fusing, to hell with trivia like explaining the energy distribution!! Whosoever 'does' p+11B will know soon enough what that alpha distribution is, what difference will having a theory for it make? (My old 'tap' analogy. You don't ask a CFD programmer to fit your plumbing, so why do you need all this theory to make a 'pronounced impact'?)
The paper has the publicity-stunt hall-marks of a sponsored put-up job to me to. But, there again, I am just a silly thicko.
Essentially, they seem to be saying that instead of having a beryllium intermediate, the reaction goes straight to three alphas, with a predictable disintegration pattern.chrismb wrote:Could someone also explain what they say with "Our results also will have a pronounced impact on the design of a possible aneutronic fusion reactor."crj11 wrote:It is interesting that the work was partly sponsored by Tri Alpha Energy
Why?
If this is true, the alpha energies are much more tightly clustered than we've been assuming, which could make direct conversion significantly easier.
That 155 degree angle seems to mean that the two high-energy alphas would come off at about 4 MeV, and the remaining one would only have around 700 keV.
Earlier studies might have been contaminated by the temperature distribution of the fusing plasma. Or these guys might be wrong; I haven't read the paper yet...
Last edited by 93143 on Mon Apr 04, 2011 10:53 pm, edited 2 times in total.
Figures 1-3 are energy spectrum plots.
After reading the actual paper, this doesn't look so good. The paper says the blastoff angle is centered at 155°, which means there's likely a range, which would mean the low-energy alphas would have a substantial spread, and would likely need to be ejected with some sort of RF resonance scheme or something, and collected with the system that catches escaped fuel ions. Not that we didn't have this problem before...
Also, the high-band alphas do have a fairly wide spread. This is probably due to the combination of high collision energy and thermal effects in the beam-target system with the spread in opening angle of the high-energy alpha pair (just pulling stuff out of the air here). A lower-temperature plasma might produce a narrower spread.
More importantly, this is specifically about the mechanism at the 675 keV resonance peak; at 2.64 MeV the beryllium pathway theory appears to be correct. I didn't see anything in the paper about other energy levels, but Polywell at least should be operating well below 675 keV, so I'm not sure this result is relevant to Polywell...
After reading the actual paper, this doesn't look so good. The paper says the blastoff angle is centered at 155°, which means there's likely a range, which would mean the low-energy alphas would have a substantial spread, and would likely need to be ejected with some sort of RF resonance scheme or something, and collected with the system that catches escaped fuel ions. Not that we didn't have this problem before...
Also, the high-band alphas do have a fairly wide spread. This is probably due to the combination of high collision energy and thermal effects in the beam-target system with the spread in opening angle of the high-energy alpha pair (just pulling stuff out of the air here). A lower-temperature plasma might produce a narrower spread.
More importantly, this is specifically about the mechanism at the 675 keV resonance peak; at 2.64 MeV the beryllium pathway theory appears to be correct. I didn't see anything in the paper about other energy levels, but Polywell at least should be operating well below 675 keV, so I'm not sure this result is relevant to Polywell...
Last edited by 93143 on Tue Apr 05, 2011 2:43 am, edited 3 times in total.
I admit I didn't understand the paper much. I thought the prevailing view was that the excited carbon 12 breaks down into a ~4 MeV alpha, and the remaining excited Beryllium 8 isotope then splits into two alphas of ~ 2.4 MeV each, for a total yield of ~ 8.8 MeV. They seem to say that all three alphas would be ~ 4 MeV for a net yield of ~ 12 MeV. This would change direct conversion considerations. It would also, relax the breakeven limits by ~ 25%.
They also mention alphas (?) of ~ 1 MeV or less for the secondary alphas (?) in the standard view, so I'm confused. Perhaps they were referring to the package that contained the two secondary alphas (IE the excited Beryllium)
Two arguments that they put forward (at least from my limited understanding) apparently is that the experimentally determined 155 degree separation angle implies the higher energy claimed. And, the calculation in reference 4, used 2 in part of the calculation, as opposed to their preferred number of 3 in calculating the energy of the secondary alphas. I think they imply that the process should be considered as an effective single step process (with an intermediate beryllium) with 3 products (alphas), instead of a process with two products- primary alpha and an excited beryllium. I think this is their explanation for the different theoretical results.
Then there is the intermediate beryllium and it's kinetic energy. I'm not sure where this fits in, perhaps that is where their ~ 1 MeV energy particle comes in(?). I suspect the paper would benefit from considerable expansion, at least for an audience that is not intimate with their jargon.
As for a sharp energy peak at 4 MeV in their spectrum, even if these secondary alphas have this precise energy, the graph would be spread by the relative speed and vectors (random?) of the parent beryllium. IE: an energy spread of 4 +/- 1 MeV from the reference frame of the detector, if my understanding is ~ right.
Dan Tibbets
They also mention alphas (?) of ~ 1 MeV or less for the secondary alphas (?) in the standard view, so I'm confused. Perhaps they were referring to the package that contained the two secondary alphas (IE the excited Beryllium)
Two arguments that they put forward (at least from my limited understanding) apparently is that the experimentally determined 155 degree separation angle implies the higher energy claimed. And, the calculation in reference 4, used 2 in part of the calculation, as opposed to their preferred number of 3 in calculating the energy of the secondary alphas. I think they imply that the process should be considered as an effective single step process (with an intermediate beryllium) with 3 products (alphas), instead of a process with two products- primary alpha and an excited beryllium. I think this is their explanation for the different theoretical results.
Then there is the intermediate beryllium and it's kinetic energy. I'm not sure where this fits in, perhaps that is where their ~ 1 MeV energy particle comes in(?). I suspect the paper would benefit from considerable expansion, at least for an audience that is not intimate with their jargon.
As for a sharp energy peak at 4 MeV in their spectrum, even if these secondary alphas have this precise energy, the graph would be spread by the relative speed and vectors (random?) of the parent beryllium. IE: an energy spread of 4 +/- 1 MeV from the reference frame of the detector, if my understanding is ~ right.
Dan Tibbets
To error is human... and I'm very human.
We know how much the reactants and products weigh, so the liberated energy is a known quantity. It's 8.7 MeV. [Unless the ¹²C* decides to remain ¹²C, in which case it's 16 MeV, which comes off almost entirely as gamma radiation...]
The idea here seems to be that there are two ~4 MeV alphas that head off from one another at a wide angle with a probability distribution centered near 155°, and a lower-energy alpha that completes the conservation of momentum picture and makes up the rest of the 8.7 MeV. There is no beryllium intermediary in this mechanism AFAICT.
Furthermore, variation in the angle between the two high-energy alphas will considerably alter the energy distribution between the three alphas; an angle of 140° results in the lower-energy alpha being around 1.6 MeV instead of 700 keV, and Fig. 5 seems to indicate significant probability of angles as low as 130°...
As you've noted, the energies and incidence angle of the reactants further modify the picture.
Again, this is at 675 keV collision energy; different colllision energies can result in different behaviours. Polywells don't operate at 675 keV, and if the plasma energy distribution is nonthermal as expected, this high-energy resonance point may not be as important in a Polywell as it might be in a Focus Fusion machine.
The idea here seems to be that there are two ~4 MeV alphas that head off from one another at a wide angle with a probability distribution centered near 155°, and a lower-energy alpha that completes the conservation of momentum picture and makes up the rest of the 8.7 MeV. There is no beryllium intermediary in this mechanism AFAICT.
Furthermore, variation in the angle between the two high-energy alphas will considerably alter the energy distribution between the three alphas; an angle of 140° results in the lower-energy alpha being around 1.6 MeV instead of 700 keV, and Fig. 5 seems to indicate significant probability of angles as low as 130°...
As you've noted, the energies and incidence angle of the reactants further modify the picture.
Again, this is at 675 keV collision energy; different colllision energies can result in different behaviours. Polywells don't operate at 675 keV, and if the plasma energy distribution is nonthermal as expected, this high-energy resonance point may not be as important in a Polywell as it might be in a Focus Fusion machine.
When I read it I thought to understand that the blastoff angle was of the "two" high energetic alphas in respect to the low energy one.93143 wrote:After reading the actual paper, this doesn't look so good. The paper says the blastoff angle is centered at 155°, which means there's likely a range, which would mean the low-energy alphas would have a substantial spread, and would likely need to be ejected with some sort of RF resonance scheme or something, and collected with the system that catches escaped fuel ions.
I.e., the 2 energetic Alfa are ejected with little spread from each other....
That wouldn't conserve momentum. If the high-energy alphas are assumed to have 4 MeV each, as stated, the "low-energy" alpha in that case would have to come off with almost twice the velocity of either of the high-energy alphas, or about 13 MeV. There isn't enough energy in the system to do that. If you constrain the energy to 8.7 MeV, you find that the "high-energy" alphas come off with about 1.6 MeV each, compared to the "low-energy" alpha's 5.4 MeV...
If, on the other hand, you assume the angle between the two high-energy alphas is 155° and constrain the total k.e. in the reaction CoM rest frame to 8.7 MeV, the high-energy alphas come off with just under 4 MeV, and the low-energy alpha is left with about 750 keV. So it looks like that's what they're describing.
If, on the other hand, you assume the angle between the two high-energy alphas is 155° and constrain the total k.e. in the reaction CoM rest frame to 8.7 MeV, the high-energy alphas come off with just under 4 MeV, and the low-energy alpha is left with about 750 keV. So it looks like that's what they're describing.