Sun in a Bottle - Charles Seife [82]
Under the right conditions, the sound waves reverberating through the liquid also cause these bubbles to compress and expand, compress and expand. Each time the bubbles are squashed by the sound waves, they heat up. If the sound waves are just right, the bubble can collapse to roughly one-tenth its original size, heating up to tens of thousands of degrees and emitting a flash of light. This is sonoluminescence.
Taleyarkhan wondered what was happening at the center of those collapsing bubbles. What would happen if you replaced water with a deuterium-laden liquid? If those bubbles got squashed far enough and became hot enough, could they induce the little bit of deuterium vapor in the center of the bubble to fuse? Could they induce a fusion reaction in a beaker?
The first problem he encountered was that tens of thousands of degrees isn’t nearly enough to induce fusion, so ordinary sonoluminescence didn’t have any hope of getting deuterium nuclei to stick together. For fusion, Taleyarkhan needed to heat deuterium and to tens of millions of degrees, a thousand times hotter than what traditional sonoluminescence could achieve. The only way to get those temperatures was to compress the bubbles far more than had ever been done before, either by squashing them tighter or by starting with bigger bubbles. Taleyarkhan had figured out an innovative way to do the latter.
His research team started with a solution of deuterated acetone, the same molecule that’s in nail polish remover, except for the fact that its six hydrogen atoms have been replaced with deuteriums. Then they irradiated the liquid with energetic neutrons and exposed it to sound waves. The energetic neutrons poured their energy into the solution and birthed very large bubbles—tens or hundreds of times larger than the ordinary bubbles in sonoluminescence—and, according to Taleyarkhan and his colleagues, the sound waves compressed them by a factor of ten thousand. This was a much higher compression than had ever been observed before. Taleyarkhan’s calculations implied that this extreme compression led to a temperature in the range of millions of degrees. This, in turn, supposedly led to fusion.
To all appearances, Taleyarkhan and his colleagues did all the right things when they went looking for deuterium-deuterium fusion. The paper told of how the researchers looked for neutrons—and found them. Tritium? Found it. They also avoided many of Pons and Fleischmann’s mistakes. They ran the obvious control experiments, substituting ordinary acetone for the deuterated variety. The neutrons and tritium disappeared. Finally, the paper convinced a science editor and a group of peer reviewers who, presumably, were satisfied with its quality.
But I was skeptical. For one thing, I knew Taleyarkhan, and while I held him in reasonably high esteem, I didn’t think of him as a fusion expert. A few years earlier—in 1999, when I was a reporter for New Scientist magazine—I had written about one of his inventions. He had figured out a clever way to make a gun that would shoot bullets at different speeds. In theory, you would be able to turn a dial on a gun and set it to “stun” with low-velocity bullets or to “kill” with high-velocity ones. (It used an aluminum-based propellant that could do things ordinary gunpowder couldn’t.) Interesting stuff, but not the sort of thing a fusion expert would invent. Taleyarkhan was a nuclear engineer, and I associated him with steam explosions and propellants and reactor safety, not fusion physics. What really bothered me, though, were the neutrons.
The bubble fusion paper was going to live or die by the neutrons Taleyarkhan was claiming to see. Neutrons were what killed Pons and Fleischmann. Neutrons were what killed ZETA. Without a nice, clear demonstration of neutrons of the proper