"At this point, we can find no evidence for anything but conventional chemistry" in the fusion experiments, said Lewis, speaking at a news conference during a meeting of the American Physical Society, the nation's largest physics organization.
Scientists from Massachusetts Institute of Technology and the Oak Ridge National Laboratory also reported that they could find no evidence to support the claims made by B. Stanley Pons of the University of Utah and Martin Fleischmann of the University of Southampton in England.
Phillip Schewe, a spokesman for the American Physical Society, which has 40,000 members, said there appeared to be little support among the society's members for the Pons-Fleischmann results. "Almost all of the findings are negative," he said, speaking about the papers that 20 groups of physicists were scheduled to give.
For the last 5 1/2 weeks, the scientific world has been in a tizzy, seeking to support the Pons-Fleischmann assertion that they have surpassed the long- sought "break even" point of nuclear fusion: producing more energy than is consumed.
If true, the development - which involves joining atomic nuclei to release vast amounts of energy - could be the scientific breakthrough of the 20th century, leading to cheap, clean, virtually unlimited energy.
But last night, their claims were strongly criticized by some of the nation's leading fusion laboratories.
Lewis said Caltech scientists have been working at a "breakneck pace" since March 23 to substantiate the cold-fusion claims. He said his team constructed an exact replica of the Pons-Fleischmann experiment and tested it with equipment far more sensitive than that used at the University of Utah.
He said they could find no evidence of excess neutrons' being emitted even though his team used neutron detectors 100,000 times more efficient than the ones used by Pons and Fleischmann. One of the known outcomes of fusion is that when the nuclei are joined into a new nucleus, large numbers of neutrons are emitted as a byproduct.
Lewis also said the Caltech team could find no evidence that extra heat was given off, an important signal that Pons and Fleischmann have cited to indicate that fusion is occurring. He said Pons and Fleischmann essentially guessed about the amount of heat the experiment should yield and when they got more they labeled that as excess heat.
Lewis also suggested that the two researchers detected excess heat because they failed to eliminate large temperature variations in their experiment by properly stirring the container's heavy water, whose atoms were involved in the reaction. Lewis said that, unless the water is stirred, the experiment would give very misleading results.
And Lewis said the Caltech team had also found no evidence of other byproducts that scientists attribute to fusion: excess helium, tritium or gamma rays.
"We have seen no evidence whatsoever for nuclear reactions or even for unusual chemical reactions," said Lewis. "We saw no evidence for neutrons, no evidence for gamma rays, no evidence for tritium and no evidence for excess heat in any of our electrochemical cells no matter how we altered the parameters of our experiment."
One of the types of helium that fusion can give off is known as helium-4, which Pons and Fleischmann said they found coming from their experiment.
But Lewis said members of the Caltech group also saw helium-4 in the experiment. They found that it was equal to the amount present in normal air. He said the Utah group failed to keep helium-4 from the air out of its experiment.
Nuclear fusion is the opposite of nuclear fission, the way power is generated in conventional nuclear reactors. Fission splits atomic nuclei to release energy; fusion forces nuclei together to produce energy. Before the Pons-Fleischmann announcement, fusion had been achieved at temperatures of at least 50 million degrees.
In another attack on the Pons-Fleischmann experiment, two MIT scientists yesterday said they believed that the two men misinterpreted crucial data.
Ronald R. Parker, director of MIT's Plasma Fusion Center, said MIT's experiments showed that far fewer neutrons were given off than Pons and Fleischmann claim.
Parker called the Pons-Fleischmann findings "a warning to not accept all the claims at face value and not to expect that there's an overnight path to nirvana as far as energy is concerned."
An 11-member team of scientists and engineers at Oak Ridge National Laboratory in Tennessee also said it could find no evidence of cold nuclear fusion. Using equipment 50,000 times more sensitive than used in the Utah experiment, the team could find no neutrons that it attributed to cold fusion, said J. Kirk Dickins of Oak Ridge.