Edwin McMillan

Edwin Mattison McMillan (September 18, 1907 – September 7, 1991) was an American physicist credited with being the first to produce a transuranium element, neptunium.

McMillan was born in Redondo Beach, California, on September 18, 1907, the son of Edwin Harbaugh McMillan and his wife Anna Marie McMillan née Mattison.

He had a younger sister, Catherine Helen, whose son John Clauser (that is, McMillan's nephew) won the Nobel Prize in Physics in 2022.

McMillan's father was a physician, as was his father's twin brother, and three of his mother's brothers.

On October 18, 1908, the family moved to Pasadena, California, where he attended McKinley Elementary School from 1913 to 1918, Grant School from 1918 to 1920, and then Pasadena High School, from which he graduated in 1924.

California Institute of Technology (Caltech) was only a mile from his home, and he attended some public lectures there.

He entered Caltech in 1924.

He did a research project with Linus Pauling as an undergraduate and received his Bachelor of Science degree in 1928 and his Master of Science degree in 1929, writing an unpublished thesis on "An improved method for the determination of the radium content of rocks".

In 1932, McMillan was awarded a National Research Council fellowship, allowing him to attend a university of his choice for postdoctoral study.

A graduate of California Institute of Technology, he earned his doctorate from Princeton University in 1933, and joined the Berkeley Radiation Laboratory where he discovered oxygen-15 and beryllium-10.

During World War II, he worked on microwave radar at the MIT Radiation Laboratory, and then on sonar at the Navy Radio and Sound Laboratory.

He then took his Doctor of Philosophy from Princeton University in 1933, writing his thesis on the "Deflection of a Beam of HCI Molecules in a Non-Homogeneous Electric Field" under the supervision of Edward Condon.

With his PhD complete, although it was not formally accepted until January 12, 1933, he accepted an offer from Ernest Lawrence at the University of California, Berkeley, to join the Berkeley Radiation Laboratory, which Lawrence had founded the year before.

McMillan's initial work there involved attempting to measure the magnetic moment of the proton, but Otto Stern and Immanuel Estermann were able to carry out these measurements first.

The main focus of the Radiation laboratory at this time was the development of the cyclotron, and McMillan, who was appointed to the faculty at Berkeley as an instructor in 1935, soon became involved in the effort.

His skill with instrumentation came to the fore, and he contributed improvements to the cyclotron.

In particular, he helped develop the process of "shimming", adjusting the cyclotron to produce a homogeneous magnetic field.

Working with M. Stanley Livingston, he discovered oxygen-15, an isotope of oxygen that emits positrons.

To produce it, they bombarded nitrogen gas with deuterons.

This was mixed with hydrogen and oxygen to produce water, which was then collected with hygroscopic calcium chloride.

Radioactivity was found concentrated in it, proving that it was in the oxygen.

This was followed by an investigation of the absorption of gamma rays produced by bombarding fluorine with protons.

In 1935, McMillan, Lawrence and Robert Thornton carried out cyclotron experiments with deuteron beams that produced a series of unexpected results.

Deuterons fused with a target nuclei, transmuting the target to a heavier isotope while ejecting a proton.

Their experiments indicated a nuclear interaction at lower energies than would be expected from a simple calculation of the Coulomb barrier between a deuteron and a target nucleus.

Berkeley theoretical physicist Robert Oppenheimer and his graduate student Melba Phillips developed the Oppenheimer–Phillips process to explain the phenomenon.

McMillan became an assistant professor in 1936, and an associate professor in 1941.

Following the discovery of nuclear fission in uranium by Otto Hahn and Fritz Strassmann in 1939, McMillan began experimenting with uranium.

He bombarded it with neutrons produced in the Radiation Laboratory's 37 in cyclotron through bombarding beryllium with deuterons.

In addition to the nuclear fission products reported by Hahn and Strassmann, they detected two unusual radioactive isotopes, one with a half-life of about 2.3 days, and the other with one of around 23 minutes.

McMillan identified the short-lived isotope as uranium-239, which had been reported by Hahn and Strassmann.

McMillan suspected that the other was an isotope of a new, undiscovered element, with an atomic number of 93.

With Samuel Ruben, he also discovered the isotope beryllium-10 in 1940.

This was both interesting and difficult to isolate due to its extraordinarily long half-life, about 1.39 million years.

In 1942 he joined the Manhattan Project, the wartime effort to create atomic bombs, and helped establish its Los Alamos Laboratory where the bombs were designed.

He led teams working on the gun-type nuclear weapon design, and also participated in the development of the implosion-type nuclear weapon.

McMillan co-invented the synchrotron with Vladimir Veksler, and after the war he returned to the Berkeley Radiation Laboratory to build them.

For this, he shared the 1951 Nobel Prize in Chemistry with Glenn Seaborg.

He was appointed associate director of the Radiation Laboratory in 1954 and promoted to deputy director in 1958.

He became director upon the death of lab founder Ernest Lawrence later that year, and remained director until his retirement in 1973.