Perpetual motion again?

3 April 2002

Researchers in the engineering department at the USA's Oak Ridge Laboratory prompted speculation and scepticism across the industry when they announced in Science that they had detected a fusion signature during experiments on sonoluminescence.

Since the Pons and Fleischman claims of "cold fusion" on a laboratory bench more than ten years ago such claims have been sceptically received. The team, which was led by Rusi Pesi Taleyarkhan, was quickly rebutted by other researchers, including some at Oak Ridge, who said they could not replicate Taleyarkhan's characteristic tritium and neutron discharges.

The claim was not dismissed out of hand, however. It is based on longstanding research into bubbles, which shows that when hit by sound waves they can implode, emitting flashes of light. In recent years the phenomenon has been extended, using ever smaller bubbles that build up enormous pressures and temperatures when they implode. The Oak Ridge researchers had used a 14MeV pulsed neutron source to nucleate bubbles in deuterium-doped acetone.

Seth Putterman of UCLA told the Los Angeles Times that researchers had speculated that conditions inside such bubbles were extreme enough to promote fusion, and Oak Ridge deputy director Lee Reidinger pointed out that the theory did not require a new mechanism for fusion to occur. But Putterman had rejected the article when asked to review it for Science, as had at least two other reviewers.

Trying to replicate the result, two Oak Ridge physicists, D Shapira and M Saltmarsh, found "no evidence for 2.5MeV neutron emission correlated with sonoluminescence" and said that tritium levels recorded in the previous experiment would require neutron emissions three magnitudes higher than had appeared in Taleyarkhan's experiment.

The Oak Ridge laboratory is planning further research.



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