Edwin McMillan

Edwin McMillan: The Man Who Named the Planet After the Element

In May 1940, working a Berkeley cyclotron that had been built mostly to smash atoms rather than build them, Edwin McMillan and chemist Philip Abelson isolated a substance nobody had seen before: the first element ever created beyond uranium on the periodic table. They named it neptunium, because Neptune is the planet beyond Uranus — a small joke with enormous consequences, since it opened the transuranium era that would soon yield plutonium, the material at the heart of the atomic bomb.

A Californian Physicist's Education

McMillan was born on September 18, 1907, in Redondo Beach, California, the son of a physician, and grew up absorbing science almost by proximity. He earned his bachelor's and master's degrees at Caltech in 1928 and 1929, then went east for his PhD at Princeton, completed in 1932 under Edward Condon with a thesis on the deflection of a molecular beam in a non-uniform electric field — a piece of precise, instrument-heavy physics that previewed the experimental temperament he would bring to Berkeley. He joined the University of California, Berkeley's Radiation Laboratory in 1932 and stayed, in one capacity or another, for the rest of his career, rising from instructor in 1935 to full professor in 1946 and eventually to director of the entire laboratory from 1958 to 1973.

Neptunium and the Transuranium Frontier

The discovery of neptunium answered a puzzle left by Enrico Fermi's earlier uranium-bombardment experiments, which had produced mysterious radioactive byproducts nobody could identify. McMillan and Abelson published their result, titled simply "Radioactive Element 93," in Physical Review on May 27, 1940. It was not an isolated curiosity: the discovery gave Glenn Seaborg, working in the same laboratory, the direct lead that produced plutonium later that same year. For that joint opening of the transuranium elements, McMillan and Seaborg shared the 1951 Nobel Prize in Chemistry "for their discoveries in the chemistry of the transuranium elements." McMillan's other laboratory work included identifying the isotopes oxygen-15 and beryllium-10, the latter notable for a half-life of roughly 1.39 million years.

The War Years and the Bomb

McMillan's career intersected directly with the Manhattan Project. He helped establish the technical specifications for the new laboratory at Los Alamos, recruited scientific personnel including Richard Feynman and Robert Wilson, and served as deputy head of the effort to develop a gun-type nuclear weapon before shifting into implosion-design work. He was present at the Trinity test on July 16, 1945, watching the first detonation of a device built on physics he had helped make possible. It was a strange position for a man whose signature discovery, only five years earlier, had been framed publicly as a matter of pure scientific curiosity about the periodic table.

Inventing the Synchrotron

McMillan's second major contribution came the same year as Trinity. In 1945 he worked out the "phase stability" principle, a method of timing the accelerating electric fields in a particle accelerator so that particles arriving slightly early or late are automatically nudged back into synchrony. The insight made it possible to build synchrotrons and synchro-cyclotrons capable of reaching far higher energies than earlier cyclotrons, whose particles fell out of step with the accelerating field as they approached the speed of light. Soviet physicist Vladimir Veksler had published a closely related idea in 1944, and the two men — who developed the concept independently, on opposite sides of a closed wartime border — shared the 1963 Atoms for Peace Award in recognition of it.

Later Career and Honors

McMillan went on to lead Berkeley's Radiation Laboratory (later Lawrence Berkeley Laboratory) for fifteen years, chaired the National Academy of Sciences from 1968 to 1971, and even worked at CERN after his formal retirement, contributing to muon magnetic moment experiments in 1974 and 1975. He held nine U.S. patents, including for the synchro-cyclotron itself, and received the National Medal of Science in 1990, a year before his death. He married Elsie Walford Blumer in 1941; their three children survived him. He suffered a stroke in 1984 and died on September 7, 1991, in El Cerrito, California, of complications from diabetes. His Nobel medal is held by the Smithsonian's National Museum of American History.

Why Edwin Is Called a Genius

McMillan's claim to genius is a craftsman's claim more than a visionary's: he was not chasing grand unification or a new theory of matter, he was solving concrete instrumental problems — how to keep particles in sync as they near light speed, how to identify a faint radioactive signal buried in cyclotron debris — and each solution happened to reorder a field. The Nobel committee's citation was for a specific discovery, not for a body of theory, and historians of physics have generally credited him with meticulous, exacting experimental judgment rather than sweeping conceptual originality. The honest counter to any "genius" label is that both of his signature achievements had close, simultaneous rivals: Abelson shared full credit for neptunium, and Veksler arrived at phase stability independently at almost the same time, which suggests the ideas were, in some sense, ready to be found by any sufficiently careful experimentalist working the same problem. What is undeniable is the density of consequential, verifiable results McMillan produced across four decades at the same laboratory bench, and the discipline required to turn two entirely different physical puzzles — nuclear chemistry and particle acceleration — into working machines within the same five-year stretch.

Legacy

Every modern synchrotron, from hospital cancer-treatment accelerators to the Large Hadron Collider's booster rings, descends from McMillan's phase-stability insight, and neptunium's discovery remains the opening chapter of the transuranium chemistry that defines nuclear science today. His nephew, physicist John Clauser, would later win his own Nobel Prize in Physics in 2022, extending a family thread of experimental rigor across generations.

Achievements

• Nobel Prize in Chemistry — 1951
• National Medal of Science — 1990
• Affiliated with University of California, Berkeley
• Educated at California Institute of Technology and Princeton University
• Worked as physicist and university teacher