Bubble fusion makes controversial return
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
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
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been replaced by deuterium (D).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 proton.
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 science."
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."
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