Bubble fusion

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.

From left to right: apparition of bubble, slow expansion, quick and sudden contraction, possible fusion event

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.

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. However, New Energy Times has reported a replication by an unrelated group at a university in Texas. (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. 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.

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.

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.

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. 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.

A report published in the journal Physical Review Letters claims further evidence of fusion. 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, in the midst of charges about research misconduct by Taleyarkhan, 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. 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."

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. 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. 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.

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. On February 7, 2007, the Purdue University administration of that time 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." 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.. A new review at Purdue has been initiated because the only papers supporting Taleyarkhan's work are those done at Taleyarkhan's lab.

See also

• Sonoluminescence — the emission of short bursts of light from imploding bubbles in a liquid when excited by sound
• Cold fusion — research continues into cold fusion into the 21st century
• List of energy topics
• Chain Reaction (film) — the fictionalized tale of a discovery and attempted cover-up of a practical fusion reactor

• The New Energy Times Special Report on Bubble Fusion/Sonofusion

External links

Repositories

• The bubble fusion controversy on New Energy Times

News

• The Strange Case of Dr. Rusi Taleyarkhan by Hal Plotkin What I Really Want to Say.com 2 February 2007
• "Bubble Power", Richard T. Lahey Jr., Rusi P. Taleyarkhan & Robert I. Nigmatulin, IEEE Spectrum Magazine, May 2005 — Readable, quantitative, illustrated article
  • "Bubble Fusion Research Under Scrutiny", IEEE Spectrum, May 2006, follow-up on May 2005 article
• R. T. Lahey Jr, R. P. Taleyarkhan, and R. I. Nigmatulin, Sonofusion — Fact or Fiction? (PDF format)
• "Possible Sound-Induced Nuclear Fusion Posited" Rensselaer Polytechnic Institute Press Release, March 5, 2002
• "Fusion controversy rekindled" BBC News, March 5, 2002
  • "Fusion experiment disappoints" BBC News, July 2, 2002
• "Evidence bubbles over to support tabletop nuclear fusion device" March 2, 2004
• "Sound waves size up sonoluminescence". PhysicsWeb. February 5, 2002
• "Researchers Report Bubble Fusion Results Replicated" Rensselaer Polytechnic Institute Press Release, March 2, 2004
• Harnessing bubbles to trigger nuclear fusion — 22 January 2005, Justin Mullins, New Scientist Magazine Issue 2483 (subscription required)
• Purdue findings support earlier nuclear fusion experiments — New positive bubble/sonofusion findings were detailed in a peer-reviewed paper appearing in the May issue of the journal Nuclear Engineering and Design. (July 12 2005)
• Bubble Fusion takes next hurdle — The potential for cavitation to induce nuclear fusion lets physicists think in new directions of energy production. (July 18 2005)
• "Desktop fusion is back on the table; Physicist claims to have definitive data, but can they be replicated?", [email protected], January 10 2006 (subscription required)
• "Sonofusion Experiment Produces Results Without External Neutron Source" PhysOrg.com January 27, 2006
• "Using Sound Waves To Induce Nuclear Fusion With No External Neutron Source" (sciencedaily.com, January 31 2006)
• "Bubble fusion: silencing the hype", Nature online, March 8, 2006 — Nature reveals serious doubts over claims for fusion in collapsing bubbles (subscription required)
• What's New, March 10, 2006 - failed replications
• "Bubble-fusion group suffer setback; Team admits a mix-up with one of their neutron detectors", May 10, 2006, [email protected] (subscription required)
• "Purdue Bubble Wraps Sonofusion Inquiry Results", June 21, 2006 Photonics.com
• "Chain Reaction" Movie, August 1996
• "Introduction to Sonofusion" Roger Stringham, October 2006
• "Practical Fusion, or Just a Bubble?", Kenneth Chang, The New York Times, February 27, 2007