For years, physicists have wanted to make a nuclear laser--one that depends on the excitation of nuclei rather than of electrons. A proposal in the 22 April Physical Review Letters suggests a path to creating such a laser, relying on some quirks of the nuclear structure of thorium. The laser would emit visible light, not the gamma rays usually associated with nuclear radiation. A nuclear laser could provide a new basis for measuring time--imagine a nuclear clock, rather than an atomic clock--and tests for many fundamental properties of nature, such as the possible variation in fundamental constants over time.
"The real gamma-ray laser is a dream of military science," says Eugene Tkalya of Moscow State University in Russia, although he says the interest from physicists has been for studying fundamental physics. Not many electronic transitions in atoms emit gamma rays, so researchers have looked to transitions in the atomic nucleus. However, the gamma-ray laser, or graser, has faced heavy skepticism, as illustrated by Los Alamos National Lab physicist Hans Frauenfelder's 1973 comment after a talk by Vitali Goldanskii of the Institute of Chemical Physics in Moscow: "Dear Vitali, I always thought a gamma laser is impossible. After your talk it seems many orders of magnitude less impossible. But still I consider it impossible."
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