Posted on 01/27/2006 9:32:09 PM PST by ckilmer
Sonofusion Experiment Produces Results Without External Neutron Source
A team of researchers from Rensselaer Polytechnic Institute, Purdue University, and the Russian Academy of Sciences has used sound waves to induce nuclear fusion without the need for an external neutron source, according to a paper in the Jan. 27 issue of Physical Review Letters.
The results address one of the most prominent questions raised after publication of the team’s earlier results in 2004, suggesting that “sonofusion” may be a viable approach to producing neutrons for a variety of applications.
By bombarding a special mixture of acetone and benzene with oscillating sound waves, the researchers caused bubbles in the mixture to expand and then violently collapse. This technique, which has been dubbed “sonofusion,” produces a shock wave that has the potential to fuse nuclei together, according to the team.
The telltale sign that fusion has occurred is the production of neutrons. Earlier experiments were criticized because the researchers used an external neutron source to produce the bubbles, and some have suggested that the neutrons detected as evidence of fusion might have been left over from this external source.
“To address the concern about the use of an external neutron source, we found a different way to run the experiment,” says Richard T. Lahey Jr., the Edward E. Hood Professor of Engineering at Rensselaer and coauthor of the paper. “The main difference here is that we are not using an external neutron source to kick the whole thing off.”
In the new setup, the researchers dissolved natural uranium in the solution, which produces bubbles through radioactive decay. “This completely obviates the need to use an external neutron source, resolving any lingering confusion associated with the possible influence of external neutrons,” says Robert Block, professor emeritus of nuclear engineering at Rensselaer and also an author of the paper.
The experiment was specifically designed to address a fundamental research question, not to make a device that would be capable of producing energy, Block says. At this stage the new device uses much more energy than it releases, but it could prove to be an inexpensive and portable source of neutrons for sensing and imaging applications.
To verify the presence of fusion, the researchers used three independent neutron detectors and one gamma ray detector. All four detectors produced the same results: a statistically significant increase in the amount of nuclear emissions due to sonofusion when compared to background levels.
As a cross-check, the experiments were repeated with the detectors at twice the original distance from the device, where the amount of neutrons decreased by a factor of about four. These results are in keeping with what would be predicted by the “inverse square law,” which provides further evidence that fusion neutrons were in fact produced inside the device, according to the researchers.
The sonofusion debate began in 2002 when the team published a paper in Science indicating that they had detected neutron emissions from the implosion of cavitation bubbles of deuterated-acetone vapor. These data were questioned because it was suggested that the researchers used inadequate instrumentation, so the team replicated the experiment with an upgraded instrumentation system that allowed data acquisition over a much longer time. This led to a 2004 paper published in Physical Review E, which was subsequently criticized because the researchers still used an external neutron source to produce the bubbles, leading to the current paper in Physical Review Letters.
The latest experiment was conducted at Purdue University. At Rensselaer and in Russia, Lahey and Robert I. Nigmatulin performed the theoretical analysis of the bubble dynamics and predicted the shock-induced pressures, temperatures, and densities in the imploding bubbles. Block helped to design, set up, and calibrate a state-of-the-art neutron and gamma ray detection system for the new experiments.
The research team leaders are all well known authorities in the field of nuclear engineering. Lahey is a fellow of both the American Nuclear Society (ANS) and the American Society of Mechanical Engineers (ASME), and is a member of the National Academy of Engineering (NAE). Block is the longtime director of the Gaerttner Linear Accelerator (LINAC) Laboratory at Rensselaer, and he is also a fellow of the ANS and recipient of their 2005 Seaborg Medal, which recognizes an individual who has made outstanding scientific or engineering research contributions to the development of peaceful uses of nuclear energy. Taleyarkhan, a fellow of the ANS and the program’s director, is currently the Ardent Bement Jr. Professor of Nuclear Engineering at Purdue University. Nigmatulin is a visiting scholar at Rensselaer, a former member of the Russian Duma, and the president of the Bashkortonstan branch of the Russian Academy of Sciences (RAS).
Source: Rensselaer Polytechnic Institute (RPI)
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Even more simply, how could a mechanical phenomena produce enough energy to cause fusion? At room temperature and pressure? There is quite a quantum hump to get over that is many orders higher than the amount of energy produced by cavitation.
It's incontrovertible that the neutrons are coming from the experimental apparatus. It remains to establish that the sonic energy is causing the neutrons to appear and that the neutrons are the result of fusion.
Uranium fission reactors are fueled by Uranium which has been enriched to increase the proportion of U-235 versus the more prevalant U-238. The fission in the reactor comes about because U-235 fission products include neutrons, which, if properly slowed by moderating materials or by distance in the Uranium, can then induce fission reactions beyond those occurring just by chance. Controlling the rate of neutron involvement in the Uranium is the mechanism which allows control of a nuclear reactor.
Now we read of an experiment which introduces Uranium and we see neutrons. Perhaps thay are coming from the Uranium. Such neutrons would behave according the inverse-square law, only proving that they emanate from the apparatus and are not just background radiation.
There should be some predictions about the energy levels of neutrons created by fission of U-235 versus those created by a proposed fusion reaction. I think there is much more to be done.
Ah more of those crazy people at my alma mater.
If anyone could make this really work, I believe they could.
I guess it's because the centre of the bubble is momentarily at extremely high pressure, and the molecules are moving very quickly into the collision area.
Looking for this experiment to be repeated.
The experiment is done by a culturally diffuse bunch of scientists at Rensselaer Polytechnic Institute, Purdue University, and the Russian Academy of Sciences
And its posted at the american physical society.
This means that the people who are in the discipline but not in the hunt are being made to sweat
Uranium-238 decays by alpha emission into thorium-234, which itself decays by beta emission to protactinium-234, which decays by beta emission to uranium-234, and so on. The various decay products, (sometimes referred to as "progeny" or "daughters") form a series starting at uranium-238. After several more alpha and beta decays, the series ends with the stable isotope lead-206.
There are no neutrons involved in the primary decay chain.
I will bet you that there is tritium somewhere in there as well as deuterium.
How energetic are the alpha particles all the way down the Uranium decay chain? Maybe what we are really seeing has nothing to do with the bubbles, or is a combination of bubble collapse energy coupled with a duterium or tritium recoil from an alpha particle collision?
They didn't say there was a lot of fusion, just some, that they could pull out of the background noise, and you can start looking for some pretty unlikely events at that level.
I'm just watching the story. Not a physicist.
The forces in the bubble collapse are strong enough to produce light. I find that interesting. A weak indicator relative to what's required for fusion.
Well, right. I was just trying to convey a sense of what's involved.
The forces in the bubble collapse are strong enough to produce light. I find that interesting. A weak indicator relative to what's required for fusion.
Right again. A light bulb produces light! Visible light energy is in the range of a few eV ( electron volts ) per photon. The proton-proton coulomb barrier is on the order of MeV ( 1e6 electron volts, ) although, due to tunneling, reactions can take place below the barrier energy. However, the reaction rate falls off exponentially as the energy drops below the threshold, so the barrier energy holds as a rule of thumb for the kinetic energy required to produce fusion.
Note that 1e6 is the difference between leaping 1 meter, and leaping 1 thousand kilometers, and this is an apt comparison since gravitational potential energy is proportional to height, on this scale.
Is there a typical level of "depletion" associated with depleted Uranium?
One of the difficulties associated with all these desktop fusion experiments has been that the signal being detected has been barely above the background noise levels. If there is something going on, there is only very little of it.
sonofusion ping
If, as it sounds, you are arguing that unless given "sun-level" condtions, fusion is impossible, regardless of scale, then how do you rationalize the Farnsworth Fusor?
Hmmm... Cars powered by champagne... :)
Ok, I read all that so let's cut to the chase... Is the Sun going to burn out soon and should we all buy gold?
There is a school of thought which asserts that the Sun cycles between two states -- fusion, and non-fusion -- and that it is currently in the non-fusing state.
According to this theory, the Sun, while it is in its fusing state, heats up, and expands, until it reaches the point at which it is no longer producing enough pressure (due to gravity) to sustain the fusion reaction. It then stops fusing, begins cooling off, and thus contracts. When it contracts to a certain point, fusion begins again, and the cycle repeats.
The evidence generally given in support of this theory consists of the cyclical ice ages, and, the "Missing Neutrinos". (The Sun, if it was fusing, would be producing more neutrinos than are currently being detected. That's right -- according to this theory, the Sun is not in its fusion mode, and we are headed toward an ice age -- one which, according to various "bits of history" we are somewhat overdue for.)
The question of "What about the missing neutrinos?" is one that we are told is answered -- by stuff that to an ignoramus like me :) sounds a wee bit too esoteric, a bit too hopeful, a bit too... unconvincing.
My guess is that the jury is still out on the theory. But to answer your question, if the Sun is in a non-fusing condition, it's only temporary. Stick around a few thousand years and everything'll be fine again (but stock up on SPF-off-the-charts for when that happens!)
As I mentioned, the conditions at the center of the sun are MINIMALLY capable of producing fusion. In an H-bomb, the temperatures are much greater for some fraction of a microsecond. I remember a physics coloquium back in the seventies when the guy was explaining the figure of merit for fusion devices - the product of confinement time, density, and temperature. He stated, jokingly, that the break-even point was 10 to the 20th, and they had achieved 10 to the 10th, "... so we like to say we are half way there." Have things progressed since then? Not so very much I think.
Gotta confess I never heard of the Farnsworth Fusor. I find several long expositions of it on the web, however, including a Wikipedia entry. Notwithstanding these, I have to stick by my guns here. I don't believe Farnsworth got anywhere near nuclear fusion. What about all these Tokomak guys? Haven't they ever heard of it? That's basically the concept conveyed by the description, sort of a miniature Tokamak. Well except they say it was supposed to be "inertial confinement". But this concept has been explored by the big boys as well. Why didn't they take the lesson of the Fusor?
And besides, if this was so great, why are they messing around with "Sonofusion" ?
What I would like to know is whether or not the stories told by his wife (and others?) are true (of his having attained sustained fusion with the device right before ITT exercised its rights to snarf it up out of his hands).
But as to the Fusor itself, yes, it's for real, and that's not at all subject to speculation. I believe that Fusors are currently used as small output sources of neutrons for various experiments.
BTW, Farnsworth is the guy who invented television (real television -- not that "spinning wheel" nonsense) back in the 1920w -- and, had it snarfed up out from under him too. He eventually won his patent battles -- too late for them to have any value.
He ended up stroking out. A loss to the world. His kind of genius does not show up nearly often enough.
For your viewing pleasure, here is a snip from a mailing list populated by genuine "rad guys" (many on the list are dot-gov employees in jobs reflecting their expertise in the field; others are in the commercial sector). Names stripped out to protect privacy. if you want to query them yourself, subscribe to CDV700CLUB on yahoogroups. I had several more archived, but when my hard drive bit the dust, my mail archives went with it :(
Regardless, if you are interested in the topic, feel free to subscribe and ask about it; I'm certain you'll get your questions answered by bona fide pros.
Snips:
------------------------------------------------------------------ This is the same technique as the "Farnsworth Fusor". Many of these have been built. Visit the folks at http://www.fusor.net/ for details. >Ok if we could tone the neutrons down a bit so there wouldnt be so >damn many per second....would this be practical to build? > >** <*****@yahoo.com> wrote: > > > >Very nice description of neutron generating tubes >in http://www.redremote.co.uk/electricstuff/ch8.pdf > >1 mA deuterons @ 1 MV hitting D2O >yields 7 billion n/sec, equiv to 100 mg worth of Ra's alpha >on Be reaction. ------------------------------------------------------------------
Regarding the Tokamaks, they really do create fusion reactions.
The thing is, they're not -- so far, at least -- sustained reactions. That's the Holy Grail of fusion. All the Tokamaks to date have consumed more energy than they produced. It's no problem to create small scale non-sustained fusion (i.e., Farnsworth Fusor or Tokamak), or, large scale sustained fusion (i.e., "city buster").
It's that stuff in between that's such a problem. (And Farnsworth may have succeeded at it!)
BTW, it was in the news the other day that China is (using money freighted to them by us, of course) going to go for the brass ring. They are going to build what they believe will be a self-sustaining Tokamak -- the world's largest fusion reactor.
If they pull it off, it'll be one more nail in our coffin.
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