Sun in a Bottle - Charles Seife [63]
MUON-CATALYZED FUSION: Ordinary atoms have large electron clouds (left) that make it hard for the nuclei to get close enough together to fuse. Replace the electrons with muons (right) and the muon cloud is much smaller; nuclei get together much more easily and are able to fuse at relatively low temperatures.
Muon-catalyzed fusion, as it came to be known, really was room-temperature fusion. If scientists could somehow replace the electrons in a jar full of hydrogen with muons, they would be able to get a fusion reaction without the need for immense heat and pressure; the muon hydrogens would fuse by virtue of their smaller size. Unfortunately, muons are hard to come by. To get them in large numbers, scientists need to build a particle accelerator. Accelerators consume lots of energy, and they are not very efficient.
Even if scientists found an efficient way of producing muons, the muons they would create would last only a few microseconds before decaying into electrons and a handful of other particles. If in those moments the scientists then successfully shot one of those muons into a cloud of hydrogen, they might get lucky and induce two atoms to fuse into helium, but what then? The muon can get trapped in the helium atom, and then it is useless. It will quickly decay without helping any other atoms to fuse. If every available muon catalyzed only one atomic fusion, then there is no hope of producing energy; merely creating the muons and delivering them would consume more energy than was released by that single fusion. If, on the other hand, a muon can escape the clutches of the helium nucleus, then helps another fusion to occur, escapes, helps another fusion, and so forth, then muon-catalyzed fusion would not be hopeless after all. If every muon induces a few hundred fusions before decaying, then perhaps it would be possible to generate more energy than the amount used to create the particles in the first place. Muon-catalyzed fusion would achieve breakeven.
When Alvarez first saw the phenomenon in deuterium, he was extremely excited. “We had a short but exhilarating experience when we thought we had solved all of the fuel problems of mankind,” he said in his Nobel Lecture a decade later. “While everyone else had been trying to solve the problem by heating hydrogen plasmas to millions of degrees, we had apparently stumbled on the solution, involving very low temperatures instead.” Unfortunately, as Alvarez’s team performed more detailed calculations, they concluded that the muons quickly got stuck in helium and decayed, and that muon-catalyzed fusion of deuterium would never lead to a practical energy source. Deuterium-tritium mixtures might fare a bit better, but the outlook was pretty grim.
Jones was more sanguine about the possibility of using muons to generate energy than Alvarez had been, and he sought to prove that muon-catalyzed fusion could, indeed, solve the world’s energy problems. With grants from the Department of Energy—the same Division of Advanced Energy Projects that Pons and Fleischmann were soon to get involved with—Jones used an accelerator at Los Alamos to zap deuterium-tritium mixtures with muons. Theory predicted that as the deuterium-tritium mixture got denser, the muon would interact with more atoms before decaying—but that this effect would be very slight. Much to his surprise, when Jones increased the density of his deuterium-tritium mixtures, he discovered that the number of interactions skyrocketed into the hundreds. By 1986, he was claiming to see 150 fusions per muon and predicted that it