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New Bubble Reaction Findings Make Fusion Claims Unlikely
By Sarah Graham
Physics Web

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 sonoluminescence.

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 m 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 22C.

At its largest, the bubble had a potential energy of several MeV, and

 

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