Since the late 1970s, Princeton physicist William Happer had been investigating spin‐exchange optical pumping as a means of polarizing nuclei. Along the way, he had given thought to practical things one might do with large collections of nuclei thus polarized, among them the enhancement of fusion in tokamaks, the creation of new kinds of polarized targets for high‐energy physics and the improvement of clinical magnetic resonance imaging. “But I was always too busy to think seriously about imaging,” Happer told us. “Then, when I came to Washington in 1991 [to become, for a time, director of energy research at DOE] I ruptured a disk and they did an mri scan of my spine. I was in great pain, and that concentrates the mind wonderfully.”

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