The latest hot potato is a paper published last week in Science [295, 1868 (2002)], in which a team led by nuclear engineer Rusi P. Taleyarkhan of Oak Ridge National Laboratory (ORNL) reports evidence suggesting that nuclear fusion may be occurring in deuterated acetone in the throes of acoustic cavitation.

The researchers bombard the liquid with powerful sound waves and carefully timed pulses of 14-MeV neutrons. The neutrons trigger the formation of tiny vapor-filled bubbles. In the ebb and flow of pressure from the sound waves, these bubbles expand dramatically and then collapse with great force, heating the vapor inside the bubbles and causing it to emit flashes of light in a process called sonoluminescence.

Scientists have long speculated that temperatures inside such imploding bubbles could reach into the millions of degrees, allowing nuclear fusion to occur.

	"We see no good reason for suppressing the paper ... critics of the result, and those who believe in it, would both do well to cool it and wait for the scientific process to do its work." Donald Kennedy, Editor-in-Chief, Science

Taleyarkhan and coworkers claim they have detected telltale evidence for such "bubble fusion." The fusion of two deuterium nuclei, knocked loose from the deuterated acetone, would be expected to produce two sets of products in approximately equal amounts: tritium and a proton, and helium-3 and a 2.45-MeV neutron. Taleyarkhan and colleagues report finding tritium above background levels in the deuterated liquid, as well as neutron emissions near 2.5 MeV. In control experiments with ordinary acetone, they do not observe tritium or neutron production.

"If the results are confirmed, [their] apparatus will be a unique tool for studying nuclear fusion reactions in the laboratory," writes nuclear physicist Frederick D. Becchetti of the University of Michigan, Ann Arbor, in a Science commentary. But he cautions that scientists should remain skeptical until the experiments are reproduced by others.

One attempt to reproduce the results has already met with failure. Nuclear physicists Dan Shapira and Michael J. Saltmarsh, also at ORNL, used the same apparatus as Taleyarkhan's group, along with a much larger neutron/gamma detector and a more sophisticated data acquisition system. But they found no evidence for 2.5-MeV neutrons correlated with the sonoluminescence, they say in an internal ORNL report that was posted on the Web (http://www.ornl.gov/slsite/SLan5av2.pdf). "Any neutron emission that might occur is at least three orders of magnitude smaller than that necessary to explain" the amount of tritium reported in the Science paper as being due to D-D fusion. Shapira and Saltmarsh did not try to verify the reported tritium production.

Taleyarkhan and coworkers dispute Shapira and Saltmarsh's findings in a detailed online rebuttal (http://www.rpi.edu/~laheyr/SciencePaper.pdf). They claim that Shapira and Saltmarsh incorrectly calibrated their detector and thus misinterpreted the findings. Taleyarkhan and coworkers reanalyzed the Shapira-Saltmarsh data, concluding that the duo actually did detect a statistically significant increase in neutron emissions.

Saltmarsh, however, says, "We stand by our data." Furthermore, he notes that "it's easy to screw up" neutron measurements, and low-level tritium measurement also is problematic.

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