Inverted Alchemy

For a thousand years alchemists dreamed of transmuting mercury into gold. They never succeeded. Modern atomic physicists might do the trick without a philosopher's stone, but do not think the result would be worth the effort. Last week, however, scientists at the University of California announced that they had transmuted gold into mercury--and turned a scientific profit. They did it by bombarding gold (atomic weight 197) with neutrons from the Berkeley cyclotron. Its atoms each absorbed one neutron, eventually turning into mercury 198.

This stunt was no mere atomic doodle. It promised the ideal measuring stick for which scientists have been crying. Since 1893, they had used as their primary standard the wavelength of a narrow band of red light in the spectrum of cadmium. Theoretically, a band of green light in the mercury spectrum would be even better: 1) the mercury atom, heavier than cadmium, gives light with a more sharply defined wavelength; 2) mercury vapor glows at low temperatures, while cadmium must be heated very hot.

But a serious obstacle blocked the use of mercury. Ordinary mercury contains several isotopes which cannot be separated chemically. Since each isotope has a slightly different atomic weight, it gives off light of slightly different wavelength. This variability makes the light of ordinary mixed mercury too fuzzy for use as a standard of measurement.

What science needed was a one-isotope mercury. The cyclotron created it by transmutation. Gold has only one isotope; mercury made from it has only one.

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