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sonofusion

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Bubble fusion or sonofusion is the common name for a nuclear fusion reaction hypothesized to occur during sonoluminescence, an extreme form of acoustic cavitation; officially, this reaction is termed acoustic inertial confinement fusion (AICF) since the inertia of the collapsing bubble wall confines the energy, causing a rise in temperature. The high temperatures producible through sonoluminescence raises the possibility that it might be a means to achieve thermonuclear fusion.[1]

Original experiments

The earliest reference to a sonofusion-type reaction is in US patent 4,333,796 filed by Hugh Flynn in 1978.

Rusi P. Taleyarkhan (ORNL) and colleagues reported in the March 8, 2002, issue of the peer-reviewed journal Science, that acoustic cavitation experiments conducted with deuterated acetone (Template:carbonTemplate:deuteriumTemplate:oxygen) show measurements of tritium and neutron output that are consistent with fusion; in addition the neutron emission was claimed to be coincident with the sonoluminescence pulse.[2]

Shock wave simulations seem to indicate that the temperatures inside the collapsing bubbles may reach up to 10 megakelvins — as hot as the center of the sun. None of the above measurements have been confirmed by a group outside of Taleyarkhan's and are highly debated, recalling the 1989 cold fusion controversy.[3][4][5][6] However, New Energy Times has reported a replication by an unrelated group at a university in Texas.[7] (Researcher Edward Forringer works at LeTourneau University, a small evangelical Christian school.) Although the apparatus operates in a room temperature environment, this is not cold fusion (as it is commonly termed in the popular press), as the claimed nuclear reactions would be occurring at the very high temperatures in the core of the imploding bubbles.

The researchers used a pulse of neutrons in order to nucleate (i.e., "seed") the tiny bubbles, whereas most previous experiments start with small air bubbles already in the liquid. Using this new method, the team was able to produce stable bubbles that could expand to nearly a millimeter in radius before collapsing. In this way, the researchers stated, they were able to create the conditions necessary to produce very high pressures and temperatures. The sensitivity of the fusion rate to temperature, which is in turn a function of how small the bubbles get when they collapse, in combination with the likely sensitivity of the latter to fine experimental details, may account for the fact that some research workers have claimed to see an effect, while others have not.

Taleyarkhan et al. also prepared identical experiments in non-deuterated (normal) acetone and failed to observe neutron emission or tritium production. Taleyarkhan got the idea of bubble fusion from his friend Dr. Mark Embrechts after a friendly post-dinner chat in 1995.

Oak Ridge replication

These experiments were repeated at Oak Ridge National Laboratory by D. Shapira and M. J. Saltmarsh with more sophisticated neutron detection equipment and they reported that the neutron release was consistent with random coincidence.[8] A rebuttal by Taleyarkhan and the other authors of the original report claimed 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. Taleyarkhan et al. report that when these differences are properly accounted for, the Shapira and Saltmarsh results are consistent with fusion.[unverified]

In addition, Galonsky has shown that by Taleyarkhan's own detector calibration the observed neutrons are too high in energy to be from a d-d fusion reaction. In a rebuttal comment, Taleyarkhan says the energy is "reasonably close" to that which is expected.[9]

In February 2005, the BBC documentary series Horizon commissioned a collaboration between Seth Putterman and Ken Suslick (two leading sonoluminescence researchers) 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. This work was reviewed by a team of four scientists, including an expert in sonoluminescence and an expert in neutron detection, who also concluded that no evidence of fusion could be observed.[10][11]

Subsequent claims of replication

In 2004, new claims of bubble fusion were made by the Taleyarkhan group, claiming that the results of previous experiments have been replicated under more stringent experimental conditions.[12][13] These results differed from the original results in that fusion was occurring for a much longer time frame than previously reported; the original report only showed neutron emission from the initial bubble collapse after the bubble nucleation whereas this report shows neutron emission many acoustic cycles later. The data however was lacking in that too large of a window was used for determination of a coincidence between the neutron emission and sonoluminescence light emission. Also, the energy of the detected neutrons was not consistent with neutrons produced from a fusion reaction. 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; also the neutron energy was again not consistent with a neutron produced from a d-d fusion reaction.[14][15]

A report published in the journal Physical Review Letters claims further evidence of fusion.[16] [17] [18] The initial news report, however, shows that the reaction does not always work correctly, and it is not known what parameters change to cause the reaction to function properly versus not function at all.

In November 2006, Edward R. "Ted" Forringer, Ph.D. and undergraduates David Robbins and Jonathan Martin of LeTourneau University presented two papers at the American Nuclear Society Winter Meeting, claiming replication of neutron emission during a visit to the meta-stable fluids research lab at Purdue University. Their experimental setup was similar to the others, using a mixture of deuterated acetone, deuterated benzene, tetrachloroethylene and uranyl nitrate and, notably, operating without an external neutron source and using two types of neutron detectors. They measured neutron levels at 8 standard deviations above the background level with a liquid scintillation detector, and 3.8 standard deviations above the background with plastic detectors. Measurements were within one standard deviation for the same experiment with a non-deuterated control liquid, demonstrating neutron production only during cavitation of the deuterated liquid.[19][20][21] After this report, Purdue's investigation cleared Taleyarkhan of the charges, stating that they "determined that the evidence does not support the allegations of research misconduct and that no further investigation of the allegations is warranted."[22]

Doubts prompt investigation

A claim as spectacular as the present one naturally arouses a lot of doubt. This culminated in a "special report" published in March 2006 by Nature, that calls into question the validity of the results of the Purdue experiments.[23] They quote Brian Naranjo of the University of California, Los Angeles with the claim that the measured spectrum is consistent with radioactive decay of the lab equipment and hence does not necessarily prove the presence of nuclear reactions.[24] 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.[25]

Doubts about the truthfulness of claims of positive observations have arisen within the Nuclear Engineering faculty of Purdue University. Because of these concerns, Purdue has initiated a review of the research, to be conducted by Purdue's Office of the Vice President for Research. In a March 9, 2006 article headed "Evidence for bubble fusion called into question", Nature reported that it had interviewed several of Taleyarkhan's colleagues who suspect something is amiss.[26] On February 7, 2007, the Purdue University committee determined that "the evidence does not support the allegations of research misconduct and that no further investigation of the allegations is warranted", and that "vigorous, open debate of the scientific merits of this new technology is the most appropriate focus going forward."[27][22] In order to verify that the investigation was properly conducted, House Representative Brad Miller requested full copies of its documents and reports by March 30, 2007.[28]. A new review at Purdue has been initiated because the only papers supporting Taleyarkhan's work are those done at Taleyarkhan's lab.

Nature's suggestion of misuse of funds ill-founded?

In July 2006, Nature publicized a claim of Seth Putterman, denied by Taleyarkhan, to the effect that DARPA funds were used to support an experiment reported in Physical Review Letters without the source being acknowledged. This may seem a matter of minor importance. Dr. Brian Josephson raised questions as to Nature's motives by pointing out that, in the article, a conspicuous display of Putterman's arguments headed "where did the money go?" is immediately followed by a paragraph devoted to "misuse of federal dollars".[29] Since Putterman does not himself consider funds were misused, it is unclear why such a paragraph should have been included if there were no intent at all to make the reader think this might have been the case.

Another problem with Nature's stance (the journal has stated "[we] believe that we have nothing to apologise for, and nothing to correct")[unverified] is that the accounting details obtained by Putterman do not appear necessarily to support his conclusions. Despite the damaging effects that the publication of a flawed allegation is likely to have had, the journal is still at this time refusing to publish a clarification.[29]

Ethical dimension

The ethical aspect of Nature's coverage of bubble fusion is complementary to that addressed in the above, and has equally been a cause of concern. Taking the Society of Professional Journalists' Code of Ethics as the norm, one may note the following in relation to the article concerned:

  1. According to the code, journalists should "test the accuracy of information from all sources and exercise care to avoid inadvertent error". As noted above, the accounting details listed in the article do not appear to support Putterman's possibly damaging conclusions: however, they are presented in the article in a way that suggests that they do.
  2. Journalists should also "make certain that headlines ... do not misrepresent. They should not oversimplify or highlight incidents out of context." Merely posing the question "Where did the money go?", which appears very conspicuously in the article, raises in the reader's mind the idea of fraud, a suggestion that the article itself does not in any way support.

New Energy Times writer Steven Krivit poses some questions about Nature's coverage in his piece "On Science, Journalism, and Nature".[30]

See also

References

  1. ↑ Chang, Kenneth (February 27, 2007). "Practical Fusion, or Just a Bubble?". New York Times. http://www.nytimes.com/2007/02/27/science/27fusion.html?8dpc. 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. At temperatures hot enough, atoms can literally fuse and release even more energy than when they split in nuclear fission, now used in nuclear power plants and weapons. Furthermore, fusion is clean in that it does not produce long-lived nuclear waste." </li>
  2. ↑ R. P., ({{{year}}}). "Evidence for Nuclear Emissions During Acoustic Cavitation," Science, 295, .
  3. ↑ Shapira, D.; M. J. Saltmarsh "Comments on Reported Nuclear Emissions during Acoustic Cavitation". (PDF) Fusion Ignition Research Experiment (FIRE) Program. URL accessed on 2007-05-13.
  4. ↑ R. P., ({{{year}}}). "Comments on the Shapira and Saltmarsh Report," {{{journal}}}, {{{volume}}}, .
  5. ↑ F., ({{{year}}}). "Evidence for Nuclear Reactions in Imploding Bubbles," Science, 295, .
  6. ↑ D., ({{{year}}}). "To Publish or Not to Publish," Science, 295, .
  7. ↑ Krivit, Steven Bubble Fusion Discoverer Taleyarkhan Strikes Back. New Energy Times, Issue 18. URL accessed on 2007-05-13.
  8. ↑ D., ({{{year}}}). "Nuclear Fusion in Collapsing Bubbles — Is it There? An Attempt to Repeat the Observation of Nuclear Emissions from Sonoluminescence," Physical Review Letters, v. 89, .
  9. ↑ A., ({{{year}}}). "Tabletop Fusion Revisited," Science, 297, .
  10. ↑ "Nuclear fusion 'put to the test'". BBC News. 17 February 2005. http://news.bbc.co.uk/2/hi/science/nature/4270297.stm. Retrieved 2007-05-13. </li>
  11. ↑ "An Experiment to Save the World". (programme transcript) Horizon. BBC News. URL accessed on 2007-05-13.
  12. ↑ Bourgeois, Theresa (2 March 2004). "Researchers Report Bubble Fusion Results Replicated: Physical Review E publishes paper on fusion experiment conducted with upgraded measurement system". RPI News & Information. http://news.rpi.edu/update.do?artcenterkey=65&setappvar=page(1). Retrieved 2007-05-13. </li>
  13. ↑ R. P., ({{{year}}}). "Additional Evidence of Nuclear Emissions During Acoustic Cavitation," Physical Review E, 69, .
  14. ↑ Venere, Emil (12 July 2005). "Purdue findings support earlier nuclear fusion experiments". Purdue News (Purdue University). http://news.uns.purdue.edu/html4ever/2005/050712.Xu.fusion.html. Retrieved 2007-05-13. </li>
  15. ↑ Y., ({{{year}}}). "Confirmatory Experiments for Nuclear Emissions During Acoustic Cavitation," Nuclear Engineering and Design, 235, pp. 1317-1324.
  16. ↑ Mark, ({{{year}}}). "Desktop fusion is back on the table," Nature.com, {{{volume}}}, .
  17. ↑ R. P., ({{{year}}}). "Nuclear Emissions During Self-Nucleated Acoustic Cavitation," Physical Review Letters, 96, . "...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..."
  18. ↑ "Using Sound Waves To Induce Nuclear Fusion With No External Neutron Source". Science Daily (Rensselaer Polytechnic Institute). 31 January 2006. http://www.sciencedaily.com/releases/2006/01/060130155542.htm. 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..." </li>
  19. ↑ "Bubble Fusion Confirmed by LETU Research". LeTourneau University News. 2006-11-17. http://www.letu.edu/opencms/opencms/events/Bubble_Fusion_Confirmed_by_LETU_Research.html. Retrieved 2006-12-05.Template:dead link </li>
  20. ↑ "Technical Sessions by Day (Wednesday)". (PDF) ANS 2006 Winter Meeting & Nuclear Technology Expo Official Program. URL accessed on 2006-12-06. (confirmation of presentation)
  21. ↑ Edward R., ({{{year}}}). "Confirmation of Neutron Production During Self-Nucleated Acoustic Cavitation," Transactions of the American Nuclear Society, v. 95, p. 736.
  22. ↑ 22.0 22.1 Chang, Kenneth (February 13, 2007). "Researcher Cleared of Misconduct, but Case Is Still Murky". New York Times: p. F-4. http://www.nytimes.com/2007/02/13/science/13purd.html. Retrieved 2007-05-13. </li>
  23. ↑ , ({{{year}}}). "Bubble fusion: silencing the hype," Nature.com, {{{volume}}}, .
  24. ↑ Brian, ({{{year}}}). "Comment on 'Nuclear Emissions During Self-Nucleated Acoustic Cavitation'," Physical Review Letters, 97, .
  25. ↑ R. P., ({{{year}}}). "Taleyarkhan et al. Reply:," Physical Review Letters, 97, .
  26. ↑ Eugenie Samuel, ({{{year}}}). "Evidence for bubble fusion called into question," Nature, 440, .
  27. ↑ "Purdue integrity panel completes research inquiry". Purdue News (Purdue University). 7 February 2007. http://news.uns.purdue.edu/x/2007a/070207BennettTaleyarkhan.html. Retrieved 2007-05-13. </li>
  28. ↑ Miller Seeks Data on Purdue Investigation Into Scientific Misconduct. House Committee on Science and Technology. URL accessed on 2007-05-13.
  29. ↑ 29.0 29.1 Josephson, Brian "Nature on the Attack". Dr. Brian Josephson website. Cavendish Laboratory, University of Cambridge. URL accessed on 2007-05-12. Includes links to correspondence and to Nature article.
  30. ↑ Krivit, Steven B. "On Science, Journalism, and Nature". New Energy Times, Issue 15. URL accessed on 2007-05-13.

    31. </ol>

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