Fusion-in-a-bubble sparks controversy
5 March 2002
Physicists in the US claim to have observed nuclear fusion in a
table-top experiment but their work has met a hostile reaction
from other researchers. Rusi Taleyarkhan of the Oak Ridge
National Laboratory and colleagues stand by their claim that
deuterium atoms fused to make tritium when gas bubbles in
deuterated acetone collapsed to generate temperatures of
millions of degrees in 'sonoluminescence' experiments (R
Taleyarkhan et al 2002 Science 295 1868). But two other
physicists at Oak Ridge have challenged the results after failing
to reproduce them in a separate experiment. Taleyarkhan and
co-workers in turn claim that the duo failed to calibrate their
instruments properly. Other sonoluminescence researchers are
sceptical, but they admit that the effect would be a major
discovery if it proves to be real.
In sonoluminescence, pulses of light
are emitted by bubbles that are forced
to expand and collapse by sound
waves. Physicists have long speculated
that the considerable compression
forces inside the bubbles when they
collapse could be large enough to
spark nuclear reactions. If this was
achieved, it could lead to an endless
source of 'clean' energy.
Taleyarkhan and co-workers at Oak
Ridge, the Rensselaer Polytechnic
Institute and the Russian Academy of Sciences claim to have seen
the tell-tale decay signals of tritium - a radioactive isotope of
hydrogen - in bubbles formed in acetone in which the ordinary
hydrogen atoms have been replaced by deuterium atoms
(C3D6O). In the experiments the bubbles are created by energetic
neutrons, and the acetone vapour in the bubbles is forced to
expand and then collapse by an acoustic signal.
The researchers back up this evidence with claims that the
bubbles also emitted neutrons with energies of 2.5 MeV - the
energy that neutrons are emitted with when two deuterium
atoms fuse. Taleyarkhan and colleagues went on to calculate that
temperatures of a million or even ten million degrees - the
temperature at the Sun's core - must exist inside the bubbles for
these reactions to proceed.
[ слишком длинный топик - автонарезка ]