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Least neutronic fusion chemistry so far?
Posted: 05 July 2012 08:39 PM   [ Ignore ]
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We call FF aneutronic, but we still use neutron shields. Have we devised any fusion that’s even less neutronic, so we can cut down on the reactor size be removing the neutron shields? If so, then could you guys list for me some reactions that would be aneutronic enough to remove the neutron shielding?

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Posted: 05 July 2012 08:54 PM   [ Ignore ]   [ # 1 ]
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Bubble-confined Sonoluminescent-laser Fusion (BSF) has no activation issues, because its fuel is emmersed within a thick blaket of coolant that safely converts neutrons into tritium. 

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Posted: 05 July 2012 11:52 PM   [ Ignore ]   [ # 2 ]
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Focus Fusion will NOT use neutron shields either… the LPP team (and other labs around the world) only get neutrons now because they are experimenting with Deuterium fuel.  And they are only fusing Deuterium so they can figure everything out.  Later this year, they should be switching to an Aneutronic fuel, Decaborane (14 Hydrogen atoms and 10 Boron atoms in one molecule). 

The number of neutrons produced by side reactions will be minuscule and of such low energy that shielding is NOT required.  Their will be some activation over time (like after weeks of operating at above 100 shots per second), but this activation will be safe enough for technicians to open the reactor after only 9 hours of being shutdown.  Not much of a concern.

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And Bubble-confined Sonoluminescent-laser Fusion (BSF) certainly doesn’t have any issues, since it only exists on paper.  Not enough research on a practical device has been done to even confirm how thick this blanket might be since the laser would have to traverse it too.  Nor do we know the energy level and penetration power of these neutrons leaving the bubble reaction.  Too slow or too fast, and they won’t interact with the heavy water (deuterium) to make Tritium. 
Nobody has even confirmed real fusion reactions taking place.  So far, some of the scientists working on it, have resigned that the temperatures needed for fusion could not be reached using bubbles.

BSF is still quite hypothetical.

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Posted: 06 July 2012 12:20 AM   [ Ignore ]   [ # 3 ]
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FF is probably going to need some neutron shielding.  The alpha particles will generate some neutrons and there isn’t much to stop it.  I don’t remember the number but I know Zapkitty commented on it a while back.  I think the number was something like 0.2% of the energy output.  If my memory is even so-so, that is 10 kW of neutrons is a big deal.  The neutron yield is enough to be a concern from a regulatory stand point.  I’m sure the activation decay is fast depending on the surrounding materials.  No energy source is perfect but some are far better than others….if they work.

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Posted: 06 July 2012 12:42 AM   [ Ignore ]   [ # 4 ]
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asymmetric_implosion - 06 July 2012 12:20 AM

FF is probably going to need some neutron shielding.  The alpha particles will generate some neutrons and there isn’t much to stop it.  I don’t remember the number but I know Zapkitty commented on it a while back.  I think the number was something like 0.2% of the energy output.  If my memory is even so-so, that is 10 kW of neutrons is a big deal.  The neutron yield is enough to be a concern from a regulatory stand point.  I’m sure the activation decay is fast depending on the surrounding materials.  No energy source is perfect but some are far better than others….if they work.

Once the Alphas are formed, wouldn’t they be very unidirectional since they are charged?  And thus, any neutrons that do happen to come from those alpha particles, also be highly directional?  If so, a shielded target just beyond the beam collection coils would only need to be fairly small.

Has Eric confirmed that 0.2% in any of his documents?  Yeah, 10 KW of neutrons would be a big deal… but depending on the energy of the average neutron, that could be mostly thermal, and NOT cause activation with most materials used in FF.

Lots of heat coming from the reaction IS already accounted for and is one of the engineering problems to be solved.  Activation may not be a problem if the average neutron is not energetic enough.  Heat, even 10 KW of heat, can be dealt with engineering.  Too much activation would require shielding since activation poses safety (and regulatory) concerns for people. 

All I remember is Eric talking about how quickly the device is ‘cool’ enough to get near after a few seconds of shutdown, and after 9 hours, is ‘cool’ enough for a technician to open the chamber and swap out the electrodes.  I don’t think he mentioned shielding being needed when using pB11 fuel.  But maybe I’m wrong.

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Posted: 06 July 2012 01:04 AM   [ Ignore ]   [ # 5 ]
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We have a document on this but I have to find it. Therre are two minor reactions. In one, the alphas, which are still trapped in the plasmoids, undergo another reaction with the boron and produce very low energy neutrons, which msut be shielded agaisnt but are too feeble to create activation in the materails we are using. We calculated that you could carry the Be anode in your pocket after it was exposed for a year.The other is a very high energy p B11 reaction whihc produces C11, with a very short lifetime (20 minutes). That is what has to decay before the device can be serviced. I know of no other fuel that produces fewer neutrons, and the main reaction pB11->3 He4 does in fact produce none.

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Posted: 06 July 2012 01:16 AM   [ Ignore ]   [ # 6 ]
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The alpha particles are directional if they travel with the ion beam.  However, directed alpha particles do not guarantee directed neutrons.  For neutron collimation, you typically require that the kinetic energy of the particle driving the reaction is greater than the energy released in the neutron producing reaction.  LLNL had shown how you get directed neutrons using specific reactions with unique properties.  However, directed neutron scatter and become isotropic neutrons. 

I agree that neutron energy is important in terms of the neutron population, but the neutrons are likely to be reasonably energetic (>500 keV) which means activation of most common materials that make up capacitors and current carrying components.  Thermal neutrons react very well with most materials so you could have a significant activation.  10 kW of heat in the context of more than 100 kW of heat is not a big deal.

The number came from a discussion on the site.  I don’t know the source.  I wouldn’t be shocked if it came from Eric or someone close to the project.  He has been working on this concept for a long while.  I’m sure he’s thought through the system and potential down falls.

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Posted: 06 July 2012 04:22 AM   [ Ignore ]   [ # 7 ]
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Lerner - 06 July 2012 01:04 AM

We have a document on this but I have to find it. There are two minor reactions. In one, the alphas, which are still trapped in the plasmoids, undergo another reaction with the boron and produce very low energy neutrons, which must be shielded against but are too feeble to create activation in the materials we are using. We calculated that you could carry the Be anode in your pocket after it was exposed for a year. The other is a very high energy p B11 reaction which produces C11, with a very short lifetime (20 minutes). That is what has to decay before the device can be serviced. I know of no other fuel that produces fewer neutrons, and the main reaction pB11->3 He4 does in fact produce none.

So, to be clear, would a pB11 FF reactor definitely need shielding to be around humans, or not?

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Posted: 06 July 2012 05:01 AM   [ Ignore ]   [ # 8 ]
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And Bubble-confined Sonoluminescent-laser Fusion (BSF) certainly doesn’t have any issues, since it only exists on paper.  Not enough research on a practical device has been done to even confirm how thick this blanket might be since the laser would have to traverse it too.  Nor do we know the energy level and penetration power of these neutrons leaving the bubble reaction.  Too slow or too fast, and they won’t interact with the heavy water (deuterium) to make Tritium. Nobody has even confirmed real fusion reactions taking place.  So far, some of the scientists working on it, have resigned that the temperatures needed for fusion could not be reached using bubbles.

BSF is still quite hypothetical.

Jo…, In BSF, external lasers do not have to transverse the blanket, the coolant material of the blanket resides inside of a spherical laser cavity, and, after that material is pumped into a state of population inversion, it functions as gain medium, just like in any other liquid laser. In the context of BSF, two coolant mixtures were examined, Li2BeF4 and a randomly chosen glass mixture having the formula (SiO2)50(PbO)10(Li2O)30(Nd2O3). The mean free path distances for 14 MeV fusion neutrons, traveling at approximately 15 meters per microsecond, were calculated to be, 7.14 cm and 5.95 cm, respectively. I think you are still confusing BSF with sonofusion; BSF does not use deuterium in heavy water to produce tritium, it uses Li in molten glass (or FLiBe), and BSF uses a high energy laser to ignite the fuel, acoustics play an insignificant role - they are only used to pre-compress the fuel and trigger the initial laser cascade. What scientists are you talking about? I’m the only person working on BSF.

So, to be clear, would a pB11 FF reactor definitely need shielding to be around humans, or not?

For a p-11B FF reactor, in addition to neutrons, large quantities of hard X-rays will be produced by bremsstrahlung, and 4, 12, and 16 MeV gamma rays will be produced by the fusion reaction. Shielding from gamma rays requires large amounts of mass, in contrast to alpha particles which can be blocked by paper or skin, and beta particles which can be shielded by foil. Gamma rays are better absorbed by materials with high atomic numbers and high density, although neither effect is important compared to the total mass per area in the path of the gamma ray. For this reason, a lead shield is only modestly better (20-30% better) as a gamma shield, than an equal mass of another shielding material such as aluminium, concrete, water or soil; lead’s major advantage is not in lower weight, but rather its compactness due to its higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta particles, but provide no protection from gamma radiation from external sources.

 

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Posted: 06 July 2012 05:15 AM   [ Ignore ]   [ # 9 ]
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Wow! Couldn’t the “onion” catch most of the X-rays? Judging by your description, these gamma rays aren’t really rare enough to ever justify zero shielding on a FF reactor, even if it’s running on pB11…

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Posted: 06 July 2012 05:33 AM   [ Ignore ]   [ # 10 ]
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The attached file comes from a wikipedia article on gamma radiation.
I don’t have permision to post it here, so please delete it if necessary.

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Pb-gamma-xs.jpg
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Posted: 06 July 2012 06:47 AM   [ Ignore ]   [ # 11 ]
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BSFusion - 06 July 2012 05:01 AM

I think you are still confusing BSF with sonofusion; BSF does not use deuterium in heavy water to produce tritium, it uses Li in molten glass (or FLiBe), and BSF uses a high energy laser to ignite the fuel, acoustics play an insignificant role - they are only used to pre-compress the fuel and trigger the initial laser cascade. What scientists are you talking about? I’m the only person working on BSF.

Sorry if I am still not seeing the major differences.  The “SF” in BSF DOES actually stand for sonofusion.  It appears to be a different approach, to the same concept.  And yes, Professor Andrea Prosperetti of Johns Hopkins HAS indeed done some work on Laser ignited Sono bubble fusion.  He concluded that it would NOT work.
http://www.experiencefestival.com/a/Sonoluminescence_-_Mechanism_of_phenomenon/id/2110704
http://www.me.jhu.edu/MENewsletter2012.pdf

I can see that you’ve done a lot of work on BSF here
http://home.centurytel.net/bubbles/bubbles.htm ...
But it is still very much in it’s infancy, and with all the stigma from Taleyarkhan, the physicist that has been found guilty of misconduct… you have to prove more than the average scientist to gain acceptance for your hypothesis.

http://www.usatoday.com/tech/science/2008-08-27-purdue-scientist_N.htm
http://articles.latimes.com/2008/jul/19/science/sci-misconduct19

 

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Posted: 06 July 2012 07:13 AM   [ Ignore ]   [ # 12 ]
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The X-Ray emissions are not really a waste product to be shielded against and/or discarded, but must be collected in “the onion” for over 40% of the total recoverable energy.

BSFusion - 06 July 2012 05:01 AM

So, to be clear, would a pB11 FF reactor definitely need shielding to be around humans, or not?

For a p-11B FF reactor, in addition to neutrons, large quantities of hard X-rays will be produced by bremsstrahlung, and 4, 12, and 16 MeV gamma rays will be produced by the fusion reaction. Shielding from gamma rays requires large amounts of mass, in contrast to alpha particles which can be blocked by paper or skin, and beta particles which can be shielded by foil. Gamma rays are better absorbed by materials with high atomic numbers and high density, although neither effect is important compared to the total mass per area in the path of the gamma ray. For this reason, a lead shield is only modestly better (20-30% better) as a gamma shield, than an equal mass of another shielding material such as aluminium, concrete, water or soil; lead’s major advantage is not in lower weight, but rather its compactness due to its higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta particles, but provide no protection from gamma radiation from external sources.

 

From what I understand, gamma emissions are extremely rare in pB11 reactions in a Dense Plasma Focus.  For a gamma to be produced, the intermediate reaction of the Carbon-12 breaking up into three He-4 (alpha particles), never occurs.  And the Carbon-12 releases it’s extra energy as an energetic photon (gamma ray).

Lerner - 07 October 2010 02:37 AM

That reaction occurs only at energies above 7Mev and even at 14 Mev, is about a million times less likely than the tri-alpha one is at 600 keV.

http://focusfusion.org/index.php/forums/viewthread/693/

So, no real shielding is needed for gamma rays either.
Eric, what shielding have you calculated will be needed for a 5MW reactor?

 

 

 

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Posted: 10 July 2012 02:09 AM   [ Ignore ]   [ # 13 ]
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Sorry if I am still not seeing the major differences. The “SF” in BSF DOES actually stand for sonofusion. It appears to be a different approach, to the same concept.

No, the accronym BSF stands for Bubble-confined Sonoluminescent-laser Fusion, as spelled out in patent appl#: 12/803901, not Bubble SonoFusion. The concepts overlap, but there are major differences. If I changed the name to Matter-confined Laser Fusion (MLF) would that eliminate your objection?

And yes, Professor Andrea Prosperetti of Johns Hopkins HAS indeed done some work on Laser ignited Sono bubble fusion. He concluded that it would NOT work.

As I said before, those links are irrelevent. Prosperetti uses a laser to create a vapor pocket inside of a tiny liquid filled tube. The focus of the laser is located a small distance away from the end of the tube, where surface tension creates a concave gas/liquid interface. The laser heats the liquid until a small vapor pocket forms. When the vapor pocket expands, it creates pressure in the surrounding liquid, which causes the concave geometry of the liquid to accelerate inward, similar to the way a “shaped charge” produces a high-speed jet of liquid metal. In summary, the article is about ink jet technology, not fusion.

One of the major advantages that BSF has over, what you are calling Prosperetti’s sonofusion, is that BSF’s laser impinges directly on the fuel, heating it to around 90eV (1,000,000 K) prior to compressing it. Laser compression, by the method of differential ionization, begins when material that is located at the periphery of the bubble is ionized, causing it to expand into the fuel, compressing and heating the fuel, until pressure (temperature and particle density) equalize. Note - the ideal ignition temperature for BSF is only 1.6 keV, much lower than the 4.3 keV of ICF.

This was all covered, in greater detail, in the patent application:

[0319] When two adjoining regions of “condensed matter” (solid or liquid) of different electron density are suddenly heated to the same extremely high temperature (high enough to fully ionize them) what will happen?

[0320] Since the temperature is the same, the radiation pressure in both regions will be the same also. The contribution of the particle pressure to the total pressure will be proportional to the particle density however. Initially, in the un-ionized state, the particle densities were about the same. Once the atoms become ionized, the particle densities can change dramatically with far more electrons becoming available from dense high-Z materials, compared to low density, low-Z materials. Even if the system is radiation dominated, with the radiation pressure far exceeding the particle pressures, the total pressures in the regions will not balance. The pressure differential will cause the high-Z material to expand, compressing the low-Z material. This type of compression is even more pronounced when low-Z gas is surrounded by high-Z condensed matter.

[0321] The process of ionization compression can be very important in a system, like BSF, where a high-Z coolant directly contacts low-Z fuel. In fact, it is interesting and relevant to note that the main effort Soviet scientists made towards an H-bomb was the “Layer Cake” or Sloika design. It employed Vitali Ginzburn’s idea of using solid lithium-deuteride fuel and Andrei Sakharov’s notion of ionization compression of the fuel…

...
But it is still very much in it’s infancy, and with all the stigma from Taleyarkhan, the physicist that has been found guilty of misconduct… you
have to prove more than the average scientist to gain acceptance for your hypothesis.

I asked you to stop, but you continue to imply that BSF has connections with Taleyarkhan and sonofusion. Why? 

 

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Posted: 10 July 2012 02:33 AM   [ Ignore ]   [ # 14 ]
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Let’s not hi-jack my thread, guys. It’s not even been stated explicitly yet (in this thread) whether DPFs will always require neutron shielding - and, furthermore, there have been several conflicting posts on this. Lerner clarified some, but this is something that I think needs to be spelled out.

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Posted: 10 July 2012 09:56 AM   [ Ignore ]   [ # 15 ]
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As far as I know you would always need neutron shielding.  The small proportion of side reactions is still enough to be concerned about, while the device is operating.    In nuclear safety the principle is of “As Low as Reasonably Achievable” (ALARA) or in the UK its known as “As Low as Reasonably Practicable” (ALARP).  Basically means if there is something you can do to lower the dosage and risk you should do it.  Any regulator would insist on it.

So the DPF device (outside the onion but inside as much else as possible) would be surrounded by a water blanket doped with boron-10, or alternatively plastic shielding tiles like Boratron.  The hydrogen in the water/plastic slows down the neutrons to a low enough speed that they can be absorbed by the B-10.  This absorption releases gamma rays, so outside the neutron shield you need a further small amount of lead or high density concrete gamma shield.

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