Edwin McMillan was born in Redondo Beach, California, on September 18, 1907. He received his bachelors degree in physics in 1928 and his masters degree the following year, both from the California Institute of Technology. In 1932 he earned his Ph.D. in physics from Princeton and in the same year became a National Research Council fellow at the University of California at Berkeley, where he worked with Ernest Orlando Lawrence (1901-1958) in the Radiation Laboratory.
One of McMillan's greatest accomplishments was his discovery of neptunium. Also known as element 93, neptunium is the element beyond uranium. The discovery was made in 1940, two years after Enrico Fermi, who had been bombarding uranium with neutrons, mistakenly thought he had produced element 93. Otto Hahn and Fritz Strassman showed that Fermi's analysis of his results was incorrect and that he had instead produced the first nuclear fission reaction.
McMillan, along with scientists throughout the world, became intrigued with the fission process. He decided to study one particular substance formed during fission, a substance with a half life of 2.3 minutes. Working with Philip Hauge Abelson, McMillan was soon able to identify the 2.3-minute substance. The two scientists showed that an isotope of uranium--uranium-239--was formed during fission. When uranium-239 decayed by beta emission, it formed a new element, number 93. Because uranium had been named after the planet Uranus, McMillan and Abelson decided to name the first of the transuranium elements after Neptune, the planet beyond Uranus. For the discovery of neptunium, McMillan was awarded a share of the 1951 Nobel Prize in chemistry.
During World War II, McMillan worked on a variety of military projects, including the development of radar, sonar, and nuclear weapons. While working at the Los Alamos Laboratory early in 1945, he made his second major scientific contribution, the theory of phase stability. Throughout the 1930s, scientists had been constructing larger and more powerful models of the cyclotron, the particle accelerator that Lawrence had developed early in the decade. By the 1940s, however, further development of this powerful research tool was hampered by an apparently inescapable problem. As the speed of particles in an accelerator increase, the particles gain mass. As they gain mass, they slow down. As they slow down, they begin to fall out of synchronization with the electrical fields that propel them. The particles fail to arrive at the point in the machine where they are accelerated and so get lost within the machine.
McMillan's idea was to alter either the electrical field or the magnetic field in the cyclotron in order to keep pace with the lagging particles. For example, as particles begin to arrive at the accelerating position later than they should, the electrical field can be slowed to match the particles' speed. McMillan coined the term synchrotron for the type of cyclotron that operates this way. He later learned that the Russian physicist, V. I. Veksler, had independently made the same suggestion at about the same time. For their introduction of the phase stability concept, McMillan and Veksler received the Atoms for Peace award in 1963.
The discovery of phase stability made the construction of larger and more powerful accelerators possible. All subsequent particle accelerators of large size have incorporated some version of McMillan's original theory.
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