Sun in a Bottle - Charles Seife [65]
Jones, Pons, and Fleischmann had entered an ever-quickening race to run experiments, prove the existence of cold fusion, write a paper for a peer-reviewed journal, and publish it. By early 1989, the competitors had agreed to submit simultaneous papers to Nature, so they could all cross the finish line simultaneously. But in a climate of increasing mistrust and antagonism, Pons and Fleischmann jumped the gun. They submitted their paper to the Journal of Electroanalytical Chemistry on March 10, and within two weeks they were in front of the microphones, touting their achievement to the world—despite the improbability of what they had found. “Stan and I often talk of doing impossible experiments,” Fleischmann said in the official University of Utah press release about cold fusion. “We each have a good track record of getting them to work.”
In truth, Pons and Fleischmann did not have the grounds for such hubris. Though they exuded confidence at the March 23 press conference, they already should have known that their data did not add up. They had several lines of evidence for the claim that they had achieved nuclear fusion in their tiny little beakers—but these lines contradicted one another.
The strongest line of evidence, as far as the chemists were concerned, was heat. When Pons and Fleischmann measured the temperature of their apparatus, their electrochemical “cell,” they discovered that the palladium was warming it up ever so slightly. Of course, many things can warm up a cell—the electricity they were running through the cell, for example, was certainly contributing to the warming—but Pons and Fleischmann argued that the energy coming from the palladium was considerably more than what they added in the form of electricity. According to Pons, an inch-long and quarter-inch-thick palladium wire brought water to a boil within minutes, and for every watt of power the scientists put in, four watts came out. More energy out than in implies a reaction of some sort. Since the reaction kept going and going, reportedly for more than one hundred hours, the amount of energy coming from the cell was too large to be explained by a chemical reaction. It was like Marie Curie’s hunk of radium; mere chemical processes couldn’t seem to explain the heat coming from the cell. To Pons and Fleischmann, this was a smoking gun of a nuclear reaction: fusion.
This sort of evidence would not convince most physicists. To them, the only way to prove that you have achieved fusion is, naturally enough, to show that you are producing some of the by-products of fusion. With deuterium-deuterium fusion, there are a few unambiguous signals that a reaction has taken place.
When two deuterium nuclei fuse (d + d), they stick together for a tiny fraction of a second: two protons and two neutrons in a quivering, energetic bundle. Because the conglomerate is so energetic, it cannot hold together completely. One particle is going to pop off and carry away some excess energy. That means either a proton (p) is going to pop off, leaving behind a tritium particle (t) with one proton and two neutrons,
d + d → p + t,
or a neutron (n) is going to pop off, leaving behind a helium-3 nucleus with two protons and one neutron,
d + d → n + 3He.
These two branches of the reaction are roughly equally likely: half of the time that you fuse two deuterium nuclei, you will get a proton and a tritium nucleus; the other half, a neutron and a helium-3 nucleus.
Free-floating protons are relatively common, but free-floating neutrons are rarer, as are tritium and helium-3. So if you think that you’ve got deuterium-deuterium fusion going on in your laboratory, the best way to convince other people is to demonstrate that you are making tritium, helium-3, and neutrons. The neutrons, arguably, should be the easiest to detect. Neutrons