1931

Deuterium

Gilbert Newton Lewis (1875–1946), Harold C. Urey (1893–1981), Ferdinand Brickwedde (1903–1989)

Deuterium (“heavy hydrogen”) is all around us, but you have to look closely. With a single extra neutron, this isotope is perfectly stable (as opposed to hydrogen with two neutrons added, which is radioactive tritium). Almost all the deuterium in the universe was probably made during the big bang. The only nuclear process that produces it in any amount is hydrogen fusion inside stars, but that deuterium gets used up faster than it’s made. Here on Earth, there are only about 150 deuterium atoms for every million ordinary hydrogen.

It was the improved mass spectrometer invented by British physicist and chemist Francis William Aston that uncovered the presence of deuterium in the 1920s. Its measured weight for hydrogen was a tiny (but real) bit lower than the weight found by chemical means, which suggested that normal hydrogen was contaminated with a bit of a heavier isotope. The name deuterium (from the Greek word for second) was suggested by American chemist Gilbert Newton Lewis, and Lewis himself was the first to prepare “heavy water,” or D₂O. American physicist Ferdinand Brickwedde concentrated deuterium by a very tedious evaporation of liquid hydrogen in 1931, and his colleague, American chemist Harold C. Urey (formerly Lewis’s student), detected it spectroscopically as deuterium’s emission spectrum grew stronger. The heavier deuterium atoms tended to stay behind, so the liquid became steadily more enriched (the same technique was used to isolate the heavier isotopes of neon detected by British physicist Joseph John Thomson in the first mass spectrometry experiment in 1913).

Deuterium was discovered seven weeks before British physicist James Chadwick discovered the neutron, but its existence made the neutron seem almost mandatory. Urey was awarded a Nobel Prize for his work, but this caused a bitter rift with Lewis, who felt (with some justification) that he’d been passed over. Deuterium is now used in everything from nuclear weapons to kinetic isotope effects.

A Hubble Space Telescope image showing a portion of the Small Magellanic Cloud, a dwarf galaxy roughly 210,000 light-years from our own. Astronomers continue to use deuterium as a tracer for star and galaxy evolution.