Bubble fusion is the common name for a nuclear fusion reaction hypothesized to occur during sonoluminescence, an extreme form of acoustic cavitation . The high temperatures produceable through sonoluminescence raises the possibility that it might be a means to achieve thermonuclear fusion.

The original experiments

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 show measurements of tritium and neutron output that is consistent with fusion. Shock wave simulations seem to indicate that the temperatures inside the collapsing bubbles may reach up to 10 million kelvins - as hot as the center of the sun. However, all of the above measurements have not been confirmed and are highly debated, recalling the 1989 cold fusion fiasco. Although the apparatus operates in a room temperature environment, this is not strictly cold fusion, 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 water. 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.

Taleyarkhan et al. also prepared identical experiments in non-deuterated (normal) acetone and failed to observe neutron emission or tritium production.

The 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.

Claims of replication in 2004

In 2004, new claims of bubble fusion were made by a team including Taleyarkhan, claiming that the results of previous experiments have been replicated under more stringent experimental conditions. [1]

References

• R. P. Taleyarkhan, C. D. West, J. S. Cho, R. T. Lahey, Jr. R. Nigmatulin, and R. C. Block, Evidence for Nuclear Emissions During Acoustic Cavitation, Science 295, 1868 (2002). (available online)
• D. Shapira, M. J. Saltmarsh. Comments on Reported Nuclear Emissions during Acoustic Cavitation, 1 March 2002. (available online (PDF))
• R. P. Taleyarkhan, R. C. Block, C. D. West and R. T. Lahey Jr., "Comments on the Shapira and Saltmarsh Report" 2 March 2002. (available online (PDF))
• F. Becchetti, Evidence for Nuclear Reactions in Imploding Bubbles, Science 295, 1850 (2002)
• D. Kennedy, To Publish or Not to Publish, Science 295, 1793 (2002)
• R. P. Taleyarkhan et al., Additional Evidence of Nuclear Emissions During Acoustic Cavitation, Physical Review E 69, 036109, 22 March 2004. (abstract available online)

External links

• Eureka Alert! story on experiments of Taleyarkhan et.al.
• Movie of the experiment: "The Sound of Neutrons" (Quicktime format)
• RPI internal magazine article, January 2000
• RPI press release, 2002
• Washington Post news story, March 5th 2002
• BBC News story, March 5th 2002
• BBC News update on experiments which failed to confirm original findings
• Evidence bubbles over to support tabletop nuclear fusion device
• "Sound waves size up sonoluminescence". PhysicsWeb. February 2002.
• RPI press release, March 2004
• Harnessing bubbles to trigger nuclear fusion - 22 January 2005, Justin Mullins, New Scientist Magazine Issue 2483 (subscription required)