Left to right: formation of bubble; slow expansion; quick and sudden contraction; purported fusion event.
Bubble fusion is the non-technical name for a nuclear fusion reaction hypothesized to occur inside extraordinarily large collapsing gas bubbles created in a liquid during acoustic cavitation. The more technical name is sonofusion.[1]
The term was coined in 2002 with the release of a report by Rusi Taleyarkhan and collaborators that claimed to have observed evidence of sonofusion. The claim was quickly surrounded by controversy, including allegations ranging from experimental error to academic fraud. Subsequent publications claiming independent verification of sonofusion were also highly controversial.
Eventually, an investigation by Purdue University found that Taleyarkhan had engaged in falsification of independent verification, and had included a student as an author on a paper when he had not participated in the research. He was subsequently stripped of his professorship. One of his funders, the Office of Naval Research reviewed the report by Purdue and barred him from federal funding for 28 months.[2]
Original experiments
Sonofusion device used by Rusi Taleyarkhan. 1. Vacuum pump 2. Liquid scintillator 3. Neutron source 4. Acoustic wave generator 5. Test chamber with fluid 6. Microphone 7. Photomultiplier tube 8. Two deuterium atoms collide 8a. Possible fusion event creating Helium and a neutron 8b. Possible fusion event creating Tritium and a proton
US patent 4,333,796,[3] filed by Hugh Flynn in 1978, appears to be the earliest documented reference to a sonofusion-type reaction.
In the March 8, 2002 issue of the peer-reviewed journal Science, Rusi P. Taleyarkhan and colleagues at the Oak Ridge National Laboratory (ORNL) reported that acoustic cavitation experiments conducted with deuteratedacetone (C3D6O) showed measurements of tritium and neutron output consistent with the occurrence of fusion. The neutron emission was also reported to be coincident with the sonoluminescence pulse, a key indicator that its source was fusion caused by the heat and pressure inside the collapsing bubbles.[4]
Oak Ridge failed replication
The results were so startling that the Oak Ridge National Laboratory asked two independent researchers, D. Shapira and M. J. Saltmarsh, to repeat the experiment using more sophisticated neutron detection equipment. They reported that the neutron release was consistent with random coincidence.[5][6] A rebuttal by Taleyarkhan and the other authors of the original report argued that the Shapira and Saltmarsh report failed to account for significant differences in experimental setup, including over an inch of shielding between the neutron detector and the sonoluminescing acetone. According to Taleyarkhan et al., when properly considering those differences, the results were consistent with fusion.[7]
As early as 2002, while experimental work was still in progress, Aaron Galonsky of Michigan State University, in a letter to the journal Science[8] expressed doubts about the claim made by the Taleyarkhan team. In Galonsky's opinion, the observed neutrons were too high in energy to be from a deuterium-deuterium (d-d) fusion reaction. In their response (published on the same page), the Taleyarkhan team provided detailed counter-arguments and concluded that the energy was "reasonably close" to that which was expected from a fusion reaction.
In February 2005 the documentary series Horizon commissioned two leading sonoluminescence researchers, Seth Putterman[9] and Kenneth S. Suslick, to reproduce Taleyarkhan's work. Using similar acoustic parameters, deuterated acetone, similar bubble nucleation, and a much more sophisticated neutron detection device, the researchers could find no evidence of a fusion reaction.[10][11]
Subsequent reports of replication
In 2004, new reports of bubble fusion were published by the Taleyarkhan group, claiming that the results of previous experiments had been replicated under more stringent experimental conditions.[12][13] These results differed from the original results in that fusion was claimed to occur over longer times than previously reported. The original report only claimed neutron emission from the initial bubble collapse following bubble nucleation, whereas this report claimed neutron emission many acoustic cycles later.
In July 2005, two of Taleyarkhan's students at Purdue University published evidence confirming the previous result. They used the same acoustic chamber, the same deuterated acetone fluid and a similar bubble nucleation system. In this report, no neutron-sonoluminescence coincidence was attempted.[14][15] An article in Nature raised issues about the validity of the research and complaints from his Purdue colleagues (see full analysis elsewhere in this page).[16][17] Charges of misconduct were raised, and Purdue University opened an investigation. It concluded in 2008 that Taleyarkhan's name should have appeared in the author list because of his deep involvement in many steps of the research, that he added one author that had not really participated in the paper just to overcome the criticism of one reviewer, and that this was part of an attempt of "an effort to falsify the scientific record by assertion of independent confirmation". The investigation did not address the validity of the experimental results.[18]
In November 2006, in the midst of accusations concerning Taleyarkhan's research standards, two different scientists visited the meta-stable fluids research lab at Purdue University to measure neutrons, using Taleyarkhan's equipment. Dr. Edward R. Forringer and undergraduates David Robbins and Jonathan Martin of LeTourneau University presented two papers at the American Nuclear Society Winter Meeting that reported replication of neutron emission. Their experimental setup was similar to previous experiments in that it used a mixture of deuterated acetone, deuterated benzene, tetrachloroethylene and uranyl nitrate. Notably, however, it operated without an external neutron source and used two types of neutron detectors. They claimed a liquid scintillation detector measured neutron levels at 8 standard deviations above the background level, while plastic detectors measured levels at 3.8 standard deviations above the background. When the same experiment was performed with non-deuterated control liquid, the measurements were within one standard deviation of background, indicating that the neutron production had only occurred during cavitation of the deuterated liquid.[20][21][22][23] William M. Bugg, emeritus physics professor at the University of Tennessee also traveled to Taleyarkhan's lab to repeat the experiment with his equipment. He also reported neutron emission, using plastic neutron detectors.[23] Taleyarkhan claimed these visits counted as independent replications by experts, but Forringer later recognized that he was not an expert, and Bugg later said that Taleyarkhan performed the experiments and he had only watched.[24]
Nature report
In March 2006, Nature published a special report that called into question the validity of the results of the Purdue experiments.[16] The report quotes Brian Naranjo of the University of California, Los Angeles to the effect that neutron energy spectrum reported in the 2006 paper by Taleyarkhan, et al. was statistically inconsistent with neutrons produced by the proposed fusion reaction and instead highly consistent with neutrons produced by the radioactive decay of Californium 252, an isotope commonly used as a laboratory neutron source.[24][25]
The response of Taleyarkhan et al., published in Physical Review Letters, attempts to refute Naranjo's hypothesis as to the cause of the neutrons detected.[26]
Tsoukalas, head of the School of Nuclear Engineering at Purdue, and several of his colleagues at Purdue, had convinced Taleyarkhan to move to Purdue and attempt a joint replication. In the 2006 Nature report they detail several troubling issues when trying to collaborate with Taleyarkhan. He reported positive results from certain set of raw data, but his colleagues had also examined that set and it only contained negative results. He never showed his colleagues the raw data corresponding to the positive results, despite several requests. He moved the equipment from a shared laboratory to his own laboratory, thus impeding review by his colleagues, and he did not give any advance warning or explanation for the move. Taleyarkhan convinced his colleagues that they should not publish a paper with their negative results. Taleyarkhan then insisted that the university's press release present his experiment as "peer-reviewed" and "independent", when the co-authors were working in his laboratory under his supervision, and his peers in the faculty were not allowed to review the data. In summary, Taleyarkhan's colleagues at Purdue said he placed obstacles to peer review of his experiments, and they had serious doubts about the validity of the research.[16][17]
Nature also revealed that the process of anonymous peer-review had not been followed, and that the journal Nuclear Engineering and Design was not independent from the authors. Taleyarkhan was co-editor of the journal, and the paper was only peer-reviewed by his co-editor, with Taleyarkhan's knowledge.[17]
In 2002, Taleyarkhan filed a patent application on behalf of the United States Department of Energy, while working in Oak Ridge. Nature reported that the patent had been rejected in 2005 by the US Patent Office. The examiner called the experiment a variation of discredited cold fusion, found that there was "no reputable evidence of record to support any allegations or claims that the invention is capable of operating as indicated", and found that there was not enough detail for others to replicate the invention. The field of fusion suffered from many flawed claims, thus the examiner asked for additional proof that the radiation was generated from fusion and not from other sources. An appeal was not filed because the Department of Energy had dropped the claim in December 2005.[27]
Doubts prompt investigation
Doubts among Purdue University's Nuclear Engineering faculty as to whether the positive results reported from sonofusion experiments conducted there were truthful prompted the university to initiate a review of the research, conducted by Purdue's Office of the Vice President for Research. In a March 9, 2006 article entitled "Evidence for bubble fusion called into question", Nature interviewed several of Taleyarkhan's colleagues who suspected something was amiss.[28]
On February 7, 2007, the Purdue University administration determined that "the evidence does not support the allegations of research misconduct and that no further investigation of the allegations is warranted". Their report also stated that "vigorous, open debate of the scientific merits of this new technology is the most appropriate focus going forward."[29][30] In order to verify that the investigation was properly conducted, House RepresentativeBrad Miller requested full copies of its documents and reports by March 30, 2007.[31] His congressional report concluded that "Purdue deviated from its own procedures in investigating this case and did not conduct a thorough investigation"; in response, Purdue announced that it would re-open its investigation.[32]
In June 2008, a multi-institutional team including Taleyarkhan published a paper in Nuclear Engineering and Design to "clear up misconceptions generated by a webposting of UCLA which served as the basis for the Nature article of March 2006", according to a press release.[33]
On July 18, 2008, Purdue University announced that a committee with members from five institutions had investigated 12 allegations of research misconduct against Rusi Taleyarkhan. It concluded that two allegations were founded—that Taleyarkhan had claimed independent confirmation of his work when in reality the apparent confirmations were done by Taleyarkhan's former students and was not as "independent" as Taleyarkhan implied, and that Taleyarkhan had included a colleague's name on one of his papers who had not actually been involved in the research ("the sole apparent motivation for the addition of Mr. Bugg was a desire to overcome a reviewer's criticism", the report concluded).[18][34]
Taleyarkhan's appeal of the report's conclusions was rejected. He said the two allegations of misconduct were trivial administrative issues and had nothing to do with the discovery of bubble nuclear fusion or the underlying science, and that "all allegations of fraud and fabrication have been dismissed as invalid and without merit — thereby supporting the underlying science and experimental data as being on solid ground".[35] A researcher questioned by the LA Times said that the report had not clarified whether bubble fusion was real or not, but that the low quality of the papers and the doubts cast by the report had destroyed Taleyarkhan's credibility with the scientific community.[36]
On August 27, 2008, he was stripped of his named Arden Bement Jr. Professorship, and forbidden to be a thesis advisor for graduate students for at least the next 3 years.[35][37]
Despite the findings against him, Taleyarkhan received a $185,000 grant from the National Science Foundation between September 2008 and August 2009 to investigate bubble fusion. In 2009 the Office of Naval Research debarred him for 28 months, until September 2011, from receiving U.S. Federal Funding. During that period his name was listed in the 'Excluded Parties List' to prevent him from receiving further grants from any government agency.[2]
Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that would allow cold fusion to occur.
Deuterium (hydrogen-2, symbol 2H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, 1H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more common 1H has no neutrons. Deuterium has a natural abundance in Earth's oceans of about one atom of deuterium in every 6,420 atoms of hydrogen. Thus, deuterium accounts for about 0.0156% by number (0.0312% by mass) of all hydrogen in the ocean: 4.85×1013 tonnes of deuterium – mainly as HOD (or 1HO2H or 1H2HO) and only rarely as D2O (or 2H2O) (Deuterium Oxide, also known as Heavy Water)– in 1.4×1018 tonnes of water. The abundance of 2H changes slightly from one kind of natural water to another (see Vienna Standard Mean Ocean Water).
The neutron is a subatomic particle, symbol n or n0 , that has no electric charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, they are both referred to as nucleons. Nucleons have a mass of approximately one atomic mass unit, or dalton. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks.
Sonoluminescence is the emission of light from imploding bubbles in a liquid when excited by sound.
This timeline of nuclear fusion is an incomplete chronological summary of significant events in the study and use of nuclear fusion.
The year 2002 in science and technology involved some significant events
Neutron generators are neutron source devices which contain compact linear particle accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuterium, tritium, or a mixture of these two isotopes into a metal hydride target which also contains deuterium, tritium or a mixture of these isotopes. Fusion of deuterium atoms results in the formation of a helium-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. Fusion of a deuterium and a tritium atom results in the formation of a helium-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV. Neutron generators have applications in medicine, security, and materials analysis.
Pyroelectric fusion refers to the technique of using pyroelectric crystals to generate high strength electrostatic fields to accelerate deuterium ions (tritium might also be used someday) into a metal hydride target also containing deuterium (or tritium) with sufficient kinetic energy to cause these ions to undergo nuclear fusion. It was reported in April 2005 by a team at UCLA. The scientists used a pyroelectric crystal heated from −34 to 7 °C (−29 to 45 °F), combined with a tungsten needle to produce an electric field of about 25 gigavolts per meter to ionize and accelerate deuterium nuclei into an erbium deuteride target. Though the energy of the deuterium ions generated by the crystal has not been directly measured, the authors used 100 keV (a temperature of about 109 K) as an estimate in their modeling. At these energy levels, two deuterium nuclei can fuse to produce a helium-3 nucleus, a 2.45 MeV neutron and bremsstrahlung. Although it makes a useful neutron generator, the apparatus is not intended for power generation since it requires far more energy than it produces.
Lithium tantalate is the inorganic compound with the formula LiTaO3. It is a white, diamagnetic, water-insoluble solid. The compound has the perovskite structure. It has optical, piezoelectric, and pyroelectric properties. Considerable information is available from commercial sources about this material.
Alpheidae is a family within the infraorder caridea characterized by having asymmetrical claws, the larger of which is typically capable of producing a loud snapping sound.
Copernicium (112Cn) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 277Cn in 1996. There are seven known radioisotopes ; the longest-lived isotope is 285Cn with a half-life of 30 seconds.
Flerovium (114Fl) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 289Fl in 1999. Flerovium has six known isotopes, along with the unconfirmed 290Fl, and possibly two nuclear isomers. The longest-lived isotope is 289Fl with a half-life of 1.9 seconds, but 290Fl may have a longer half-life of 19 seconds.
Neutron detection is the effective detection of neutrons entering a well-positioned detector. There are two key aspects to effective neutron detection: hardware and software. Detection hardware refers to the kind of neutron detector used and to the electronics used in the detection setup. Further, the hardware setup also defines key experimental parameters, such as source-detector distance, solid angle and detector shielding. Detection software consists of analysis tools that perform tasks such as graphical analysis to measure the number and energies of neutrons striking the detector.
A bubble is a globule of a gas substance in a liquid. In the opposite case, a globule of a liquid in a gas, is called a drop. Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.
Rusi P. Taleyarkhan is a nuclear engineer and has been a faculty member in the Department of Nuclear Engineering at Purdue University since 2003. Prior to that, he was on staff at the Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee. He obtained his Bachelor of Technology degree in mechanical engineering from the Indian Institute of Technology, Madras in 1977 and MS and PhD degrees from Rensselaer Polytechnic Institute (RPI) in 1978 and 1982 respectively. He also holds an MBA from RPI.
Kenneth S. Suslick is the Marvin T. Schmidt Professor of Chemistry Emeritus at the University of Illinois at Urbana–Champaign. His area of focus is on the chemical and physical effects of ultrasound, sonochemistry, and sonoluminescence. In addition, he has worked in the fields of artificial and machine olfaction, electronic nose technology, chemical sensor arrays, and the use of colorimetric sensor arrays as an optoelectronic nose.
Sonoluminescence is a phenomenon that occurs when a small gas bubble is acoustically suspended and periodically driven in a liquid solution at ultrasonic frequencies, resulting in bubble collapse, cavitation, and light emission. The thermal energy that is released from the bubble collapse is so great that it can cause weak light emission. The mechanism of the light emission remains uncertain, but some of the current theories, which are categorized under either thermal or electrical processes, are Bremsstrahlung radiation, argon rectification hypothesis, and hot spot. Some researchers are beginning to favor thermal process explanations as temperature differences have consistently been observed with different methods of spectral analysis. In order to understand the light emission mechanism, it is important to know what is happening in the bubble's interior and at the bubble's surface.
Timothy Grant Leighton is a British scientist who was a Professor of Ultrasonics and Underwater Acoustics at the University of Southampton. He is the inventor-in-chief of Sloan Water Technology Ltd., a company founded around his inventions. He is an academician of three national academies. Trained in physics and theoretical physics, he works across physical, medical, biological, social and ocean sciences, fluid dynamics and engineering. He joined the Institute of Sound and Vibration Research (ISVR) at the University of Southampton in 1992 as a lecturer in underwater acoustics, and completed the monograph The Acoustic Bubble in the same year. He was awarded a personal chair at the age of 35 and has authored over 400 publications.
Seth J. Putterman is an American physicist. He is known to have an eclectic approach to research topics that broadly revolves around energy-focusing phenomena in nonlinear, continuous systems, with particular interest in turbulence, sonoluminescence, sonofusion and pyrofusion.
References
↑ Chang, Kenneth (February 27, 2007). "Practical Fusion, or Just a Bubble?". The New York Times. Retrieved 2007-02-27. Dr. Putterman's approach is to use sound waves, called sonofusion or bubble fusion, to expand and collapse tiny bubbles, generating ultrahot temperatures.
↑ G. M. McCracken, Peter E. Stott (2005). "false trails". Fusion: the energy of the universe. Complementary science series (illustrateded.). Elsevier Academic Press. pp.91–92. ISBN978-0-12-481851-4.
↑ Peplow, Mark (10 January 2006). "Desktop fusion is back on the table". Nature. doi:10.1038/news060109-5.
Taleyarkhan, R. P.; C. D. West; R. T. Lahey; R. I. Nigmatulin; J. S. Cho; R. C. Block; Y. Xu (January 2006). "Nuclear Emissions During Self-Nucleated Acoustic Cavitation". Physical Review Letters. 96 (letter 034301): 034301. Bibcode:2006PhRvL..96c4301T. doi:10.1103/PhysRevLett.96.034301. PMID16486709. S2CID30633034. ...Statistically significant nuclear emissions were observed for deuterated benzene and acetone mixtures but not for heavy water. The measured neutron energy was <=2.45 MeV, which is indicative of deuterium-deuterium (D-D) fusion. Neutron emission rates were in the range ~5×103 n/s to ~104 n/s and followed the inverse law dependence with distance...
"Using Sound Waves To Induce Nuclear Fusion With No External Neutron Source". Science Daily. Rensselaer Polytechnic Institute. 31 January 2006. Retrieved 2007-05-13. "...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...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..."
↑ "Bubble Fusion Confirmed by LETU Research" LeTourneau University News (www.letu.edu/opencms/opencms/events/Bubble_Fusion_Confirmed_by_LETU_Research.html) link inactive as of 2008-05-10
↑ "Technical Sessions by Day (Wednesday)"(PDF). ANS 2006 Winter Meeting & Nuclear Technology Expo Official Program. November 12–16, 2006. p.24. Archived from the original(PDF) on 2007-06-21. Retrieved 2006-12-06. (confirmation of presentation)
↑ Forringer, Edward R.; David Robbins; Jonathan Martin (12 November 2006). "Confirmation of Neutron Production During Self-Nucleated Acoustic Cavitation". Transactions of the American Nuclear Society. v.95: 736. ISSN0003-018X.
1 2 "Bubble Fusion Research Under Scrutiny", IEEE Spectrum, May 2006
Seife, Charles (November 2009). "Bubble Trouble". Sun in a Bottle: The Strange History of Fusion and the Science of Wishful Thinking. Penguin. pp.171–200. ISBN978-0-14-311634-9. Retrieved 24 September 2011.
Peplow, M.A.R.K. (January 10, 2006). "Desktop fusion is back on the table; Physicist claims to have definitive data, but can they be replicated?". Nature News. doi:10.1038/news060109-5.
"Bubble fusion: silencing the hype", Nature online, March 8, 2006 — Nature reveals serious doubts over reports of fusion in collapsing bubbles (subscription required)
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