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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 579 #2
March 5, 2002
By Phillip F. Schewe, Ben Stein, and James Riordon

Has Nuclear Fusion Been Observed in a Bubble Tank?
A team of scientists has claimed evidence for deuterium-deuterium fusion in a tabletop apparatus at Oak Ridge National Lab (Taleyarkhan et al. (.pdf format), Science, 8 March 2002), but other scientists (including a separate group at Oak Ridge) are raising serious concerns about the validity of the result.

In their experiment, Taleyarkhan et al. (a collaboration of scientists from Oak Ridge, Rensselaer Polytechnic Institute and the Russian Academy of Sciences) utilize sonoluminescence (SL), itself a well-studied and highly regarded area of research (see, for example, Updates 34, 299, 307, 327, and 355), in which powerful sound waves sent into a liquid tank trigger the creation of single or multiple bubbles which then collapse and release short flashes of light.

Sonoluminescence, literally the conversion of sound into light, is a remarkable process in that sound itself is not a densely packed form of energy. Even the sound in the most powerful car stereo has a much lower energy density than the light in a penlight laser beam.

In an SL experiment, however, the energy from the sound wave gets focused into a very small region, namely a collapsing bubble. This highly concentrated energy heats the gas inside the bubble to incandescent temperatures resulting in the release of light. The conversion of sound energy into light energy represents an energy concentration of over a trillion.

Researchers have long speculated whether the conditions inside the collapsing bubbles could be made to approach the high temperatures and densities necessary to trigger energy-producing nuclear fusion reactions such as those that occur inside the sun. This is a great matter of debate, as some details of the bubble collapse and light emission are still incompletely understood.

With this incomplete knowledge, researchers cannot discount the possibility that the conditions can be tweaked to generate nuclear fusion, modest as these fusion reactions are likely to be.

However, according to leading sonoluminescence theorist William Moss of Lawrence Livermore National Laboratory, "We are all pretty sure that normal SL conditions are nowhere near fusion temperatures--typical SL temperatures don't exceed 11,000 degrees Kelvin or so, at least from theoretical estimates"---as opposed to the millions of degrees that nuclear fusion would typically require.
(More: Physics News Update Source)
2002 © Physics News Update.

Dan