Rabi’s technique was based on the resonance principle first described by Irish physicist Joseph Larmor, and it enabled more precise measurements of nuclear magnetic moments than had ever been previously possible. Rabi’s method was later independently improved upon by physicists Edward Purcell and Felix Bloch, whose work on nuclear magnetic resonance (NMR) garnered them the 1952 Nobel Prize in Physics and laid the foundations for magnetic resonance imaging (MRI).
Rabi was born in Rymanów, a town in what was then known as the Austro-Hungarian Empire but is now part of Poland, on July 29, 1898. His family immigrated to the United States the following year and settled in New York City. Like many other immigrants at the time, Rabi’s father made ends meet by working a variety of jobs, such as delivering ice and laboring in factories. An adherent of Orthodox Judaism, the elder Rabi hoped his son would become a rabbi, but religious questions arose in the mind of the younger Rabi when he read a book on the Copernican system of planetary motion. Science, not religion, appeared to be Isidor Rabi’s calling.
Rabi attended Manual Technical Training High School in Brooklyn, and his excellent academic performance won him scholarships that helped him afford classes at Cornell University following graduation. In 1919, Rabi completed his bachelor’s degree in chemistry. He worked for a few years as a chemist, but soon decided to return to Cornell for graduate studies. Realizing he preferred physics over chemistry, Rabi changed his course of study and transferred to Columbia University in 1923. Although quantum physics was not being taught in American universities at that time, Rabi found the topic fascinating and joined other physics students in an attempt to bring the field to the school. He even gave a departmental seminar on an important experiment carried out in 1922 by Otto Stern and Walther Gerlach in which they used a molecular beam to observe the magnetic properties of atomic nuclei. In 1926, Rabi married Helen Newmark. The couple later had two children. The year after his marriage, Rabi obtained a Ph.D. in physics.
Rabi traveled to Europe for post-graduate study. There he met many of the pioneers of quantum physics, including Niels Bohr, Werner Heisenberg and Otto Stern. He spent the majority of his time overseas in Stern’s laboratory in Germany, where he observed and performed experiments using the Stern-Gerlach molecular beam method. This work would have a tremendous impact on the direction Rabi’s research would take when he returned to the United States in 1929. In the fall of that year, Rabi began lecturing at Columbia. He had obtained a post there during a time period when it was difficult for Jews to attain academic appointments thanks to an excellent recommendation from Heisenberg. Rabi continued his association with Columbia throughout the rest of his career, with the exception of a leave of absence he took during the war years.
In the early 1930s, Rabi began his own molecular beam research. His initial goal was to record the nuclear spin of sodium. Becoming frustrated with the methods then available for such research, Rabi developed his own technique. Essentially Rabi adapted and built upon the molecular beam method he saw demonstrated in Germany by Stern. Whereas Stern’s apparatus involved the application of a single, strong magnetic field to deflect atoms, Rabi’s made use of three deflecting fields, two of which were weak. Because of the multiple fields, the sodium atoms in the beam studied by Rabi experienced three deflections. These deflections depended on the magnetic moments of the atoms and atomic nuclei. Rabi’s method of determining magnetic moments proved to be much more precise than the earlier method of Stern and Gerlach. After he used his technique to study sodium, Rabi and his associates continued to employ it to make increasingly accurate measurements of the magnetic properties of many other atoms.
Rabi’s molecular beam work was first published in 1937. By the time he won the Nobel Prize in Physics for this work, Rabi’s research had taken a drastic turn. Due to the United States’ involvement in World War II, Rabi left Columbia for the Massachusetts Institute of Technology, where critical radar research was taking place at the Radiation Laboratory. Rabi initially headed the research division and later became the associate director of the lab. Despite an invitation to serve as associate director of the Manhattan Project directed by J. Robert Oppenheimer, Rabi remained at the “Rad Lab” until the end of the war because he firmly believed in the importance of radar research. Nevertheless, he often served as a consultant on the Manhattan Project and frequently visited Los Alamos.
Once the war concluded, Rabi and other prominent American scientists returned to the academic posts they had temporarily vacated. Rabi was appointed chair of the Columbia physics department. Through his efforts, the department became one of the best in the world. Columbia recognized Rabi’s considerable contributions in 1964 by naming him University Professor, the institution’s greatest academic distinction.
Rabi’s administrative skills, however, extended far beyond the reaches of Columbia University. He played key roles in the foundation and organization of a number of prestigious research institutions, including Brookhaven National Laboratory, the Nevis Laboratory in Columbia physics department and the European Center for Nuclear Research (CERN). He also held several important advisory and committee positions. The NATO Science Committee, the UN Committee on the Peaceful Uses of Atomic Energy and the General Advisory Committee of the Atomic Energy Commission were just a few of the groups that benefited from Rabi’s service.
Rabi passed away following a prolonged illness on January 11, 1988, in New York. Shortly before his death, Rabi experienced first-hand the practical offspring of his magnetic resonance work when doctors used MRI to aid in his diagnosis.