Edwin McMillan

1907 - 1991

Edwin M. McMillan: Architect of the Transuranium Era and Modern Accelerators

Edwin Mattison McMillan (1907–1991) was a titan of 20th-century science whose work fundamentally altered our understanding of the building blocks of the universe. A physicist by training but a Nobel laureate in chemistry, McMillan’s career spanned the most transformative years of nuclear physics. He is best remembered for discovering the first element heavier than uranium and for inventing the "phase stability" principle, which liberated particle accelerators from their early energy limits.

1. Biography: From the Pacific Coast to the Frontiers of Matter

Edwin McMillan was born on September 18, 1907, in Redondo Beach, California. Raised in Pasadena, he was immersed in a scientifically rich environment from a young age. He attended the California Institute of Technology (Caltech), earning his B.S. in 1928 and M.S. in 1929. At Caltech, he was mentored by the legendary Linus Pauling, an experience that honed his meticulous experimental style.

He moved east to Princeton University for his doctoral work, completing his Ph.D. in 1932 under Edward Condon. His thesis focused on the deflection of a beam of HCl molecules in a non-homogeneous electric field.

In 1932, McMillan returned to California to join Ernest O. Lawrence’s "Radiation Laboratory" (now Lawrence Berkeley National Laboratory) at UC Berkeley. He remained affiliated with Berkeley for the rest of his career, rising from a research fellow to a full professor and eventually succeeding Lawrence as the Director of the Laboratory in 1958. During World War II, his academic career was interrupted by high-stakes defense work, including radar development at MIT and a pivotal role in the Manhattan Project at Los Alamos.

2. Major Contributions: Transuranics and Phase Stability

The Discovery of Neptunium (Element 93)

In 1940, the periodic table ended at Uranium (atomic number 92). Many believed heavier elements could not exist or were too unstable to be found. Using the 60-inch cyclotron at Berkeley, McMillan bombarded uranium with slow neutrons. He noticed a unique radioactive signature with a half-life of 2.3 days that did not behave like any known element. Collaborating with Philip Abelson, he proved this was a new element—the first "transuranium" element. They named it Neptunium, following the planetary sequence (Uranus → Neptune).

The Path to Plutonium

While studying Neptunium, McMillan identified a second radioactive substance that he suspected was element 94. However, before he could definitively prove its existence, he was called away to assist with the development of radar for the war effort. He left his notes with Glenn T. Seaborg, who completed the identification of Plutonium.

The Synchrotron and Phase Stability

By 1945, early cyclotrons had hit a "relativistic ceiling." As particles reached high speeds, their mass increased (as predicted by Einstein), causing them to fall out of step with the accelerator's pulses. McMillan independently conceived of the principle of phase stability. This allowed the frequency of the accelerating field to be synchronized with the changing mass and orbit of the particles. This breakthrough led to the development of the synchrocyclotron and the synchrotron, the ancestors of today’s Large Hadron Collider. (The Soviet physicist Vladimir Veksler discovered this principle independently at roughly the same time).

3. Notable Publications

McMillan’s bibliography is characterized by concise, high-impact papers that reported paradigm-shifting results.

"Radioactive Element 93" (1940), Physical Review: Co-authored with Philip Abelson, this paper announced the discovery of neptunium and provided the first proof that elements beyond uranium could be synthesized.
"The Synchrotron—A Proposed High Energy Particle Accelerator" (1945), Physical Review: This landmark paper described the phase stability principle, providing the theoretical blueprint for modern high-energy physics.
"Production of Mesons by X-Rays" (1949), Science: This work detailed early experiments using the Berkeley synchrotron to produce subatomic particles, bridging the gap between nuclear physics and particle physics.

4. Awards & Recognition

McMillan’s contributions were recognized at the highest levels of international science:

Nobel Prize in Chemistry (1951): Shared with Glenn T. Seaborg "for their discoveries in the chemistry of the transuranium elements."
Atoms for Peace Award (1963): Shared with Vladimir Veksler for the independent discovery of the phase stability principle.
National Medal of Science (1990): Awarded by President George H.W. Bush shortly before McMillan's death.
Member of the National Academy of Sciences (1947): He served as a core advisor to the U.S. government on nuclear policy for decades.

5. Impact & Legacy

McMillan’s legacy is twofold: he expanded the map of the chemical world and provided the tools to explore it.

The Synthetic Universe: His discovery of Neptunium broke the "uranium barrier," leading to the synthesis of over 20 additional elements. This work is the foundation of modern nuclear medicine (e.g., Americium in smoke detectors, Plutonium in space batteries).
The Era of "Big Science": As the Director of the Lawrence Berkeley Laboratory (1958–1973), McMillan oversaw the transition of physics into the era of large-scale, multi-disciplinary research teams.
High-Energy Physics: Every modern circular accelerator operates on the principle of phase stability. Without McMillan’s insight, the study of quarks, Higgs bosons, and other fundamental particles would have been impossible.

6. Collaborations

McMillan was a quintessential "Rad Lab" scientist, thriving in the collaborative, high-energy atmosphere of Berkeley.

Ernest O. Lawrence: McMillan was Lawrence’s "right-hand man" for years, translating Lawrence’s broad visions into functional experimental hardware.
Glenn T. Seaborg: Though their personalities differed—McMillan was reserved and meticulous, Seaborg was a prolific administrator and communicator—their partnership redefined the periodic table.
J. Robert Oppenheimer: At Los Alamos, McMillan was a key leader in the "Gun Division," working on the design of the Hiroshima bomb (Little Boy) before moving to the implosion design team.
Elsie Blumer: In a notable personal-professional crossover, McMillan married Elsie Blumer, the sister of Ernest Lawrence’s wife, Molly, making the two giants of Berkeley physics brothers-in-law.

7. Lesser-Known Facts

The "Missed" Nobel for Plutonium: While McMillan shared the Nobel for transuranium elements, many historians note that had he not been pulled away for war work in 1940, he likely would have been the sole discoverer of Plutonium. He never expressed bitterness, once remarking that:
the war work was simply a "duty that had to be done."
A Renaissance Man: Outside the lab, McMillan was an avid mountain climber and a skilled amateur photographer. He was known for his "green thumb" and spent much of his retirement tending to his extensive garden in the Berkeley hills.
The "Quiet" Director: Unlike the boisterous Ernest Lawrence, McMillan was known for a quiet, contemplative leadership style. He was famous for walking through the lab and asking researchers incredibly pointed, difficult questions that often exposed flaws in their experimental logic.
Radar Pioneer: Before going to Los Alamos, McMillan helped develop the microwave radar systems at MIT’s Radiation Lab, technology that was arguably as decisive in winning WWII as the atomic bomb.