Bubble fusion makes controversial return
4 March 2004
The physicist who claimed to have observed nuclear fusion in a beaker of
acetone two years ago has published new data to back up his claim. Rusi
Taleyarkhan, now at Purdue University in Indiana, and colleagues say that
fusion neutrons and tritium are produced when the acetone is subjected to
intense sound waves in a table-top sonoluminescence experiment (R
Taleyarkhan et al. 2004 Phys. Rev. E to be published). However, other
physicists continue to doubt the experiment.
In sonoluminescence, the bubbles in a liquid emit light when they are forced
to expand and collapse by sound waves. Physicists believe that the pressures
and temperatures inside the collapsing bubbles could be high enough to
initiate nuclear reactions. If achieved, such "bubble fusion" could lead to
a new clean energy source.
In a controversial paper published in Science in March 2002 Taleyarkhan and
co-workers described how they had used high-energy neutrons to create tiny
bubbles of gas in a beaker of acetone in which the hydrogen atoms had been
replaced by deuterium (D). Taleyarkhan, who was then based at the Oak Ridge
National Laboratory, claimed that the temperature inside the collapsing
bubbles was in excess of a million degrees - high enough for two deuterium
nuclei to undergo a fusion reaction (Science 295 1868). DD fusion reactions
can produce a helium-3 nucleus plus a neutron, or a tritium nucleus and a
However, the results were questioned by many researchers in the field. Now,
Taleyarkhan says his team has repeated the experiment with more sensitive
detectors. "A fair amount of very substantial new work has been conducted,"
he said in a press release issued by Purdue. "And this time I made a
conscious decision to involve as many individuals as possible - top
scientists and physicists from around the world and experts in neutron
As before, the team claims to detect tritium as well as neutrons with the
characteristic energy for DD fusion reactions. Moreover, the fusion products
are not observed in experiments with ordinary acetone. Taleyarkhan says that
chances of the result being due a phenomenon other than fusion have been
reduced from 1 in 100 to 1 in 1011.
Michael Saltmarsh of Oak Ridge says he is "intrigued but sceptical" about
the new work. "Unlike their Science paper, most of the background notes and
supporting information seem to be correct but there are still some puzzling
inconsistencies," he told PhysicsWeb. "In particular, the estimated neutron
detection efficiency is still an order of magnitude too low. While better
than the Science article, the difference would produce a mismatch between
the reported neutron and tritium yields."
"Thermonuclear sono-fusion may not be impossible," says Willy Moss of the
Lawrence Livermore National Lab, "but more tests need to done. Personally, I
would like the results to be real, but I believe that the nature of these
claims requires absolute proof."
"When a startling new discovery is announced, it is the responsibility of
the authors to lay things clear," adds Aaron Galonsky of Michigan State
University. "Taleyarkhan and co-workers have not done that well enough for
me to be able to say whether they have seen nuclear fusion in a bottle of
acetone. With two million 14 MeV neutrons per second injected into the room
where the experiment was performed, there are opportunities for error in
detecting the much rarer, lower-energy sonoluminescent neutrons."
Belle Dumé is Science Writer at PhysicsWeb
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