Image: Courtesy of Oak Ridge National Laboratory, Rensselaer Polytechnic Institute and the Russian Academy of Sciences (Rusi P. Taleyarkhan, J. S. Cho, C.D. West, R.T. Lahey,Jr., R.I. Nigmatulin and R.C. Block)
Donald Kennedy, editor of the prestigious journal Science, knew he was in for a row if he published the paper. It¿s not that the work was shoddy or came out of left field. On the contrary, the experiments had been performed with great care by well-respected senior scientists at Oak Ridge National Laboratory (ORNL), Rensselaer Polytechnic Institute (RPI) and the Russian Academy of Sciences.
But what the authors were claiming was just so extraordinary: that nuclear fusion reactions, of the sort that power stars and hydrogen bombs, had been created on a lab bench using little more than a vibrating ring, a neutron gun and a beaker of specially prepared acetone. Add to that the fact, reported in the Washington Post, that at least three of the experts to which the article had been sent for peer review urged Science to reject it. And finally there was the follow-up study (not yet subjected to peer review) by another team at Oak Ridge that claimed that the evidence of fusion reactions disappeared when it repeated the experiment with different sensors and analyzed the data in a different way.
"It goes without saying that we cannot publish papers with a guarantee that every result is right," Kennedy hedged in an editorial that accompanied the article in the March 8, 2002, issue of Science. "What we are very sure of is that publication is the right option, even¿and perhaps especially¿when there is some controversy.
Controversy is the only thing assured to follow an experiment that so resembles the "cold fusion" fiasco of 1989, when Stanley Pons and Martin Fleishmann of the University of Utah said that they had discovered room-temperature reactions; the announcement became headline news but was soon discredited. There are important differences, however. In this case the scientists who believe they have found a new route to fusion have suggested a plausible mechanism by which it could occur. And they have discovered two genuinely odd anomalies that conventional physics cannot easily explain.
The phenomenon, as described by Rusi Peri Taleyarkhan of ORNL, Richard T. Lahey of RPI and their coinvestigators, happened when they were studying sonoluminescence¿light created by sound. German scientists first observed sonoluminescence in the 1930s, when they immersed sonar loudspeakers in water baths. But it wasn¿t until the past decade that scientists worked out many of the details.
What we call sound is really a series of moving pressure fronts. The pressure at a fixed point swings from low to high and back as the sound wave sweeps by. If the sound is loud enough and at the right frequency, the pressure at the trough of the wave will be so low that the fluid will boil, producing microscopic bubbles. When the high pressure front at the crest of the sound wave slams into these bubbles, they implode, and shock waves focus the energy of the implosion to a central region of atomic dimensions. The temperature at that central point skyrockets above 10,000 degrees Celsius, the pressure zooms to 10,000 atmospheres and a flash of light emerges for just a few picoseconds. The bigger the bubble, the more energy in the implosion, and the hotter and brighter the sonoluminescent flash.
Star in a Jar
Standard sonoluminescence experiments use water. Taleyarkhan¿s group used an organic chemical called acetone, an ingredient in common nail-polish remover, because it is rich in neutron-absorbing carbon and hydrogen atoms. The researchers then loaded up the acetone with extra neutrons in two ways. First, they used acetone made from deuterium, which is hydrogen with an extra neutron. Second, they put the flask of acetone next to a source of neutron radiation, in one case a chunk of plutonium-beryllium and in other cases a neutron pulse gun.