Kenneth Bainbridge

Kenneth Tompkins Bainbridge (July 27, 1904 – July 14, 1996) was an American physicist at Harvard University who worked on cyclotron research.

His accurate measurements of mass differences between nuclear isotopes allowed him to confirm Albert Einstein's mass–energy equivalence concept.

Kenneth Tompkins Bainbridge was born in Cooperstown, New York, on July 27, 1904.

He was educated at Horace Mann School in New York.

While at high school he developed an interest in ham radio which inspired him to enter Massachusetts Institute of Technology (MIT) in 1921 to study electrical engineering.

In five years he earned both Bachelor of Science (S.B.) and Master of Science (S.M.) degrees.

During the summer breaks he worked at General Electric's laboratories in Lynn, Massachusetts and Schenectady, New York.

While there he obtained three patents related to photoelectric tubes.

Normally this would have been a promising start to a career at General Electric, but it made Bainbridge aware of how interested he was in physics.

Upon graduating from MIT in 1926, he enrolled at Princeton University, where Karl T. Compton, a consultant to General Electric, was on the faculty.

In 1929, he was awarded a Ph.D. in his new field, writing his thesis on "A search for element 87 by analysis of positive rays" under the supervision of Henry DeWolf Smyth.

Bainbridge enjoyed a series of prestigious fellowships after graduation.

He was awarded a National Research Council, and then a Bartol Research Foundation fellowship.

At the time the Franklin Institute's Bartol Research Foundation was located on the Swarthmore College campus in Pennsylvania, and was directed by W. F. G. Swann, an English physicist with an interest in nuclear physics.

Bainbridge married Margaret ("Peg") Pitkin, a member of the Swarthmore teaching faculty, in September 1931.

They had a son, Martin Keeler, and two daughters, Joan and Margaret Tomkins.

In 1932, Bainbridge developed a mass spectrometer with a resolving power of 600 and a relative precision of one part in 10,000.

He used this instrument to verify Albert Einstein's mass–energy equivalence, E = mc2.

Francis William Aston wrote that:

"By establishing accurate comparisons of the masses of the light particles concerned in nuclear disintegrations, particularly that of 7Li, discovered by Cockcroft and Walton, he achieved a noteworthy triumph in the experimental proof of the fundamental theory of Einstein of the equivalence of mass and energy."

In 1933, Bainbridge was awarded a prestigious Guggenheim Fellowship, which he used to travel to England and work at Ernest Rutherford's Cavendish Laboratory at Cambridge University.

While there he continued his work developing the mass spectrograph, and became friends with the British physicist John Cockcroft.

When his Guggenheim fellowship expired in September 1934, he returned to the United States, where he accepted an associate professorship at Harvard University.

He started by building a new mass spectrograph that he had designed with at the Cavendish Laboratory.

Working with J. Curry Street, he commenced work on a cyclotron.

They had a design for a 37 in cyclotron provided by Ernest Lawrence, but decided to build a 42 in cyclotron instead.

Bainbridge was elected a Fellow of the American Academy of Arts and Sciences in 1937.

His interest in mass spectroscopy led naturally to an interest in the relative abundance of isotopes.

The discovery of nuclear fission in uranium-235 led to an interest in separating this isotope.

He proposed using a Holweck pump to produce the vacuum necessary for this work, and enlisted George B. Kistiakowsky and E. Bright Wilson to help.

There was little interest in their work because research was being carried out elsewhere.

In September 1940, with World War II raging in Europe, the British Tizard Mission brought a number of new technologies to the United States, including a cavity magnetron, a high-powered device that generates microwaves using the interaction of a stream of electrons with a magnetic field.

This device, which promised to revolutionize radar, demolished any thoughts the Americans had entertained about their technological leadership.

Alfred Lee Loomis of the National Defense Research Committee established the Radiation Laboratory at the Massachusetts Institute of Technology to develop this radar technology.

In 1943, their cyclotron was requisitioned by Edwin McMillan for use by the U. S. Army.

It was packed up and carted off to Los Alamos, New Mexico.

He was the Director of the Manhattan Project's Trinity nuclear test, which took place July 16, 1945.

Bainbridge described the Trinity explosion as a "foul and awesome display".

He remarked to J. Robert Oppenheimer immediately after the test, "Now we are all sons of bitches."

This marked the beginning of his dedication to ending the testing of nuclear weapons and to efforts to maintain civilian control of future developments in that field.