New Bubble Reaction Findings Make Fusion Claims Unlikely
By Sarah Graham
July 24, 2002
A new study has cast further doubt on controversial claims made
earlier this year that nuclear fusion was achieved in a bench-top
'sonoluminescence' experiment. In the first measurements of their
kind, Yuri Didenko and Kenneth Suslick of the University of
Illinois in the US tracked the processes that occurred in a single
bubble in water when it was compressed by pulses of sound.
They conclude that endothermic chemical reactions would make
it "exceedingly difficult" to reach the high temperatures needed to
spark nuclear fusion in such bubbles (Y Didenko and K Suslick
2002 Nature 418 394).
Bubbles trapped in a liquid can be forced
to expand and contract by firing acoustic
pulses into the liquid. When a bubble
expands, molecules from the surrounding
liquid evaporate into it. This vapour is then
compressed when the bubble contracts,
and can reach temperatures and pressures
that are high enough to kick-start chemical
reactions and spark the emission of light -
a phenomenon known as
In March, physicists in the US caused a stir when they claimed to have
seen deuterium nuclei fuse in bubbles in 'deuterated' acetone. The
team led by Rusi Taleyarkhan of Oak Ridge National Laboratory
calculated that the temperature inside the bubbles must have reached
tens of millions of degrees for the reaction to proceed. But many
researchers working in the field dismissed these claims.
Now Didenko and Suslick have shed some light on the controversy by
studying how the acoustic energy is distributed between chemical
reactions, light emission and bubble collapse during
sonoluminescence. To do this, they created a bubble - which was 30
µm across - in a water-filled cell, and made it oscillate using an
acoustic signal with a frequency of 52 kHz.
To monitor the production of hydroxyl ions, nitrous oxide ions and
photons in the bubble - which contained air and water vapour - the pair
used fluorescence techniques and spectroscopy. Measurements were
made at both 3 and 22°C.
At its largest, the bubble had a potential energy of several MeV, and
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