Kenneth (Ken) Tompkins Bainbridge

BIOGRAPHICAL MEMOIR

July 27, 1904 — July 14, 1996

By Richard Wilson

INTRODUCTION

Many people remember KENNETH TOMPKINS BAINBRIDGE for his famous remark to J Robert Oppenheimer on the morning of July 16, immediately after the first atomic bomb test at Alamagordo, New Mexico "Now we are all sons of bitches". This contrasted with Oppenheimer’s sophisticated thought of the line from the Bhagavad Gita: "I have become Death; the Destroyer of Worlds". But Ken, an outstanding experimenter, was always more direct in his approach. Ken was recognized early in his scientific career for his precise measurements of mass differences between nuclear isotopes with the mass spectrograph he had designed. When compared to the energies of decay radiations, these confirmed Einstein’s massenergy equivalency. In collaboration with the late J. Curry Street he designed and built a small cyclotron at Harvard University that was later sent to Los Alamos, New Mexico. Even before the USA entered WW II Bainbridge joined the Radiation Laboratory at MIT developing microwave radar, particularly highpowered systems, spending 2 ½ years there. In the spring of 1943 he transferred to the nuclear weapons project at Los Alamos. Starting in 1945, he built a new , moire precise, mass spectrograph, began the construction of a new cyclotron, and was able to measure changes in the decay rates of some radioactive nuclei resulting from differing molecular bonding and from physical compression.

EARLY YEARS 1904 - 1929

Kenneth Bainbridge was born on July 27, 1904, in Cooperstown, New York. When he was Chairman of the Harvard physics department in 1955, Paul Fenimore Cooper, Jr., joined the department as a graduate student and I remember them reminiscing about Cooperstown at one of the Department picnics. However, Ken grew up in New York City, attending the Horace Mann School and the Horace Mann High School. The Bainbridge family lived on Riverside Drive near 158th Street and the Hudson River where just after World War I returning naval vessels docked. Ken, interested in radio at high school, put an antenna on the family’s rooftop. Ship radio operators would knock on his door to investigate. Ken bought from his callers 5watt vacuum tubes from his callers for a couple of dollars. Thereby he set up a radiotelephone, obtained a radio amateur license, and operated a "ham" station with call letters 2WN.

In 1921 Ken entered MIT to study electrical engineering in a five-year cooperative program with the General Electric Company. In the summers he worked at one of the General Electric facilities, firstly in Lynn, Massachusetts, and then mostly at the Research Laboratories in Schenectady, New York. As an outgrowth of his work there, Ken obtained a couple of patents on photocells. After completion, with both an S.M. and a S.B degree he changed his direction to physics. Karl T. Compton a consultant to G.E. recognized Ken’s quality, and recruited him for graduate work at Princeton where he was head of the physics department.. Ken remembered, with pleasant amusement, his interview with Dean West and quoted him as saying, "You're nice boys, but it's too bad you never went to college". It was at Princeton that Ken began his life-long interest in mass spectroscopy. His first searched for the then undetected element 87 of the periodic table, an element that should behave chemically as a heavy alkali. But his search was unfruitful and it was left to Marguerite Perey at the Radium Institute of Paris, to find element 87 and call it "francium". This disappointment, discouraged Ken, but did not stop him.

POST DOCTORAL APPOINTMENTS 1929-1934

After completing his Ph.D. program at Princeton, Ken Bainbridge spent four years, first as a National Research Council fellow and then as a Bartol Research Foundation fellow, at the Franklin Institute's Bartol Research Foundation. The "Bartol" was directed by W. F. G. Swann, who was especially interested in research on cosmic rays and nuclear physics. Ken always thought of Swann as an eccentric Englishman, but this Englishman (RW) considers the adjective unnecessary! Ken continued to develop his mass spectrographs at Bartol and undertook precise nuclear mass measurements to confirm the massenergy equivalence, E = Mc2. While at Bartol, in September 1931 Ken married Margaret ("Peg") Pitkin, then a member of the Swarthmore teaching faculty. .

In the summer of 1933 Ken joined Lord Ernest Rutherford's Cavendish Laboratory, who was a world leader in experimental nuclear physics. In a later year Ken described how Rutherford stopped him in passing in a corridor to ridicule as obviously impractical a suggestion just made to him by a visitor, Leo Szilard, for a nuclear chain reaction based on protons. Szilard went on to envisage a much more practical process involving neutrons, which, of course, only became reality after neutroninduced uranium fission was discovered. At Cambridge Ken began a continuing close friendship with John (later Sir John) D. Cockroft which became important later. Peg accompanied Ken to Cambridge and Martin K. Bainbridge, their first child was born there in 1933.

PREWAR ACADEMIA 1934- 1939

In September of 1934 Ken returned to the United States and joined the faculty in the physics department at Harvard University where he later became the first George Vasmer Leverett Professor of Physics. He built and employed an improved mass spectrograph that he had designed during his sojourn at the Cavendish Laboratory and proposed a method of modifying isotopic abundance using gaseous counter-flow in a Holweck molecular vacuum pump. In 1935, Ken led the construction of a cyclotron as a joint project between the Graduate School of Engineering, represented by Professor Harry Mimno with Ken and Jabez (Curry) Street representing the physics department. But it was Ken and Curry who were the primary workers. The cyclotron was complete in 1938 and the report of the physics department in 1939 states that radioactive materials supplied to Harvard Medical School, New York Memorial Hospital and Massachusetts General Hospital in addition to uses for physics at Woods Hole Meteorological Station, MIT physics department and members of Williams College and Purdue University. It supported the work of 14 researchers in Harvard departments. According to the late Roger Hickman the construction cost was about $40,000 of which about $20,000 came from the Rockefeller Foundation which then funded medical research. The Bainbridge's two daughters Joan Bainbridge Safford and Margaret Tomkins (Bainbridge) Robinson were born in Cambridge, Massachusetts.

THE WAR YEARS 1939-1945

In 1939 Ken became concerned about the rise of Naziism in 1939 as Europe became embroiled in World War II. When Britain sent the Tizard Mission in September of 1940, sharing their military secrets, Ken took a leave of absence from Harvard and joined E.O. Lawrence in the newly formed Radiation Laboratory at the Massachusetts Institute of Technology to develop microwave "radar". There he spent 2 ½ years. While there Ken interacted with the local Raytheon company. Years later, he remembered that they “fixed” a speeding ticket for him - a favor he would have preferred not to have received! Ken's friendship with British physicists, especially with Cockroft, who had been a scientist member of the Tizard Mission, became an invaluable asset. In 1941 he was selected to go on a visit to England in 1941 to gain information not only about the radar program. He commented later “At that time I was brighter, quicker, younger and of higher standing in science than I am now.” He also learned of British progress toward releasing nuclear energy while attending a meeting of the Maud Committee, which was overseeing that effort in Britain. Ken's particular project at the Radiation Laboratory was the push toward higherpowered radars, especially for the Navy. He found the Navy at that time the most technically oriented of the U. S. military services and the least handicapped by protocols related to military rank. This experience was reflected in his concern about the organization of Los Alamos, where he was recruited in May of 1943, which operated under the Manhattan District of the U. S. Army and General Leslie R. Groves. well before the family moved to Los Alamos.

While at Los Alamos it became clear that a cyclotron was needed to measure various nuclear reaction cross sections of interest, and supplement the work already being ably carried out at the Princeton cyclotron. Ken knew where one was to be found - at Harvard. Discussions began at a high administrative, and top secret level, between Harvard President James B. Conant (then away from Cambridge) and General Groves and it was agreed that Harvard would sell the cyclotron to the US government for $1 with an informal promise of a cyclotron to replace it when the war was over. Since the atomic bomb project was top secret, the purpose of the purchase had to be disguised from those not cleared for secret information. A medical physicist, Dr Hymer Friedell, accompanied the young cyclotron and nuclear physics expert Robert Wilson. The "cover story" is that the cyclotron was needed for medical treatment of military personnel and it was sent to St Louis to be forwarded to an "unknown destination".

At Los Alamos early in 1944, at the request of George Kistiakowsky and Director J. Robert Oppenheimer, Ken undertook the oversight of the design of high explosive assemblies and the preparations for a fullscale test of a nuclear bomb. In articles in the Bulletin of the Atomic Scientists in 1975, Ken lucidly described the search for an appropriate site, the preparations, and the successful carrying out of the test early in the morning of July 16, 1945. The second of those stories was entitled: "A Foul and Awesome Display." His immediate thought on witnessing the first explosion was relief that the test was successful; for if not, he would have had to find out what had gone wrong. His famous remark noted in the introduction, 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.

RETURN TO ACADEMIC LIFE 1945 - 1969

In the fall of 1945 Ken returned to academic science at Harvard. He undertook to build a large mass spectrograph, designed for high resolution of masses and to replace the prewar cyclotron with a much more powerful one utilizing the then newly invented concept of synchronous acceleration. At a conference in Cambridge, England in 1947, Ken described the project. “The neutron beam will be directed straight to the divinity school” he said. At that time he handed over the task firstly to Robert (Bob) R. Wilson, who had joined the physics department at Harvard after the end of the war and then to Norman F. Ramsey who joined Harvard in 1947. Alas, the cyclotron design had been completed before discovery of the pi meson and the energy of the new synchrocyclotron turned out to be just less than required for pion production. For about a dozen years the new Harvard cyclotron was employed for many scattering experiments and other studies of nucleonnucleon forces and of nuclear structure. During construction, Ken insisted to his students that it was for nuclear research and not for medical work. One of the students, David Bodansky recalls him saying “There will be no rats running around THIS cyclotron.” He was shortly contradicted when one of the first experiments was, in fact, irradiation of animals! The operating life of the cyclotron was greatly extended when it became a facility for research on the use and clinical applications of the highly focused proton beam in collaborative projects with staff members from the Massachusetts General Hospital. It was shut down finally on June 2nd 2002, when its role was taken over by an even more powerful, and flexible dedicated machine at the hospital, enabling further expansion of the important clinical applications developed using the physics cyclotron.

Ken devoted much of his energy just after the war to designing for the Harvard physics department an advanced laboratory in nuclear physics intended as a course of study for graduate students. Because of the many new students underwritten by the GI Bill, the number of graduate students in physics was far greater than had been the norm before the war. Nuclear physics had gained new visibility and popularity from its contributions to winning the war. Students gained their first experience in activities preparing them for research in experimental physics in Ken's meticulously designed and documented laboratory. The experiments ranged from a replica of J. J. Thompson's positive ray apparatus (a precursor of mass spectrographs) through a bent crystal Xray spectrograph, a 180 degree betaray spectrograph using the then new technique of NMR for field calibration, to analysis of tracks in photographic emulsions to identify muons. As a part of Ken's dislike of the development and testing of nuclear weapons, he set up a facility associated with his laboratory of nuclear physics to collect and measure radioactive fallout. It is noteworthy that he measured fall out from the first Chinese bomb test as soon as the fall out arrived in Massachusetts. In his fundamental research he built balanced ionization chambers with which he was able to determine changes in lifetimes of several longlived isomers, which decay by internal electron conversion when their atoms are differently bonded chemically or are subjected to physical compression. In addition to constructing his large mass spectrograph to make precise measurements of mass differences among pairs, he built an elegant doublefocusing electron spectrograph. In the years before his retirement in 1975, Ken devoted much of his time to improving his graduate student advanced laboratory which is now integrated with the laboratory for advanced undergraduates.