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Here's the programme details. If you want the
programme transcript it is available on
http://www.bbc.co.uk/sn/tvradio/programmes/horizon/experiment_prog_summary.shtml
In March 2002, the scientific world was rocked by some astonishing
news: a distinguished US government scientist claimed he had made nuclear
fusion out of sound waves in his laboratory.
Rusi Taleyarkhan's breakthrough was such important news because nuclear
fusion is one of the most difficult scientific processes, and also one of
the most coveted. It could solve all of our energy problems for ever. In
principle, sufficient fuel exists on earth to provide clean,
pollution-free energy for billions of people for millions of years.
To make it happen, individual atoms must be slammed into each other
with enough energy to make them fuse together, something that requires
temperatures found only in the core of stars like our Sun � over 10
million Kelvin. The idea that these temperatures had been reached in a
small scale laboratory using only soundwaves took many scientists by
surprise. To them, fusion projects were huge multibillion-pound,
intergovernmental schemes with the far off goal of producing energy in
several decades time.
Taleyarkhan's fusion breakthrough was based on a little-understood
process called sonoluminescence. It's a process that magically transforms
sound waves into flashes of light, focusing the sound energy into a tiny
flickering hot spot inside a bubble. It's been called the star in a
jar.
The star in a jar effortlessly reaches temperatures of tens of
thousands of degrees, hotter than the surface of the sun. Many scientists
had wondered if the core of the bubble was even hotter � maybe even as hot
as the core of the sun. If so, fusion would happen there. But until
Taleyarkhan, no one had been able to either prove it or disprove it.
The breakthrough and the paper in Science attracted great scepticism.
When fusion takes place, particles called neutrons are given off. These
are considered by scientists to be the key signature of nuclear fusion �
but measuring neutrons on a small, laboratory scale had proven notoriously
difficult in the past � and had even killed off an infamous fusion claim
in 1989. Many scientists didn't believe that Rusi Taleyarkhan' neutron
detection was absolutely right. So to get to the bottom of the issue, the
experiment was re-run by Mike Saltmarsh and Dan Shapiro, colleagues at the
Oak Ridge National Laboratory. They couldn't find any evidence of fusion.
But the controversy escalated as Taleyarkhan's team stood their ground and
then, two years later, brought out a new paper showing even more fusion
and more neutrons. This paper was thoroughly reviewed and published in
another respected journal.
But the the controversy wouldn't die down. Nuclear fusion from
soundwaves would be a huge scientific breakthrough � and to be convinced
of it, many scientists wanted to see better evidence, evidence that was
absolutely incontrovertible. They wanted to look very precisely at the
timing of the neutrons to see just how closely they were related to the
flashes of light.
If they occurred at the exact same time, they would finally be
convinced that fusion was taking place. But they wanted timing with
incredible accuracy, that of a nanosecond, or a billionth of a second.
This was one measurement that, though possible, still hadn't been carried
out by Taleyarkhan and his team.
So Horizon decided to try to sort out the issue once and for all. And
we commissioned an independent team of leading scientists to conduct the
experiment. Working from the instructions set out in Taleyarkhan's paper,
we assembled the same key scientific conditions to create nuclear fusion
from sonoluminescence. To see if we could find fusion, we measured the
neutrons and the flashes of light simultaneously with nanosecond accuracy,
something that had never been done before.
The experiment was carried out by Seth Putterman, one of the world's
leading practitioners of sonoluminescence. His data was analysed by a
panel in the UK that included experts in sonoluminescence and neutron
detection. They agreed that Putterman had achieved the vital scientific
conditions set out in Taleyarkhan's paper and that his experiment was a
good attempt at getting the same results.
But then it came down to the crucial question: did Putterman find
fusion? The result was negative. Recording data nanosecond by nanosecond,
Putterman did not find a single neutron close enough to a flash of light
for it to be considered the result of nuclear fusion.
We put our conclusion to Taleyarkhan. He said that several differences
in our equipment could have affected our results. It is very possible that
other laboratories around the world will reproduce Rusi Taleyarkhan's
fusion results but until then, the claim will continue to attract great
scepticism from the wider scientific
community. | 
