Eduard Persell American physicist, Nobel Prize winner in physics in 1952 Date of Birth: 30.08.1912 Country: USA

1. Biography of Edward Purcell
2. Contributions to Microwave Radar and Nuclear Magnetic Resonance
3. The Development of Nuclear Magnetic Resonance
4. Contributions to Astronomy and Teaching
5. Honors and Retirement

Biography of Edward Purcell

American physicist Edward Mills Purcell was born in Taylorville, Illinois, to Edward A. Purcell and Mary Elizabeth (née Miley) Purcell. He received his primary and secondary education in the public schools of Taylorville and Mattoon, Illinois. In 1929, Purcell enrolled at Purdue University in Lafayette, Indiana, where he developed an interest in physics while working towards a degree in electrical engineering. After spending a year as an exchange student at the Technical University of Karlsruhe in Germany, Purcell pursued a Ph.D. in physics at Harvard University, receiving his master's degree in 1936 and his doctorate in 1938. He remained at Harvard as a lecturer until 1940.

Contributions to Microwave Radar and Nuclear Magnetic Resonance

During World War II, Purcell joined the Radiation Laboratory at the Massachusetts Institute of Technology (MIT), where he led a group conducting fundamental research on the generation and detection of microwaves. It was during this time that he came into contact with Isidor Rabi, who was studying the properties of atoms and molecules using radio waves. In 1946, Purcell returned to Harvard as an adjunct professor of physics and became a full professor in 1949. His knowledge of microwave and radiofrequency radiation, acquired during the development of radar systems, was instrumental in his research on nuclear magnetic moments, for which he later received the Nobel Prize.

The Development of Nuclear Magnetic Resonance

In the 1930s, Rabi proposed a method for measuring magnetic moments using radio waves, but his technique required sample evaporation. Purcell set out to develop a method that not only preserved the sample but also surpassed Rabi's method in accuracy. Around the same time, Felix Bloch from Stanford University, who also contributed to radar technology during the war, independently developed a similar method. Both researchers proposed methods for measuring nuclear magnetic moments based on the phenomenon of nuclear precession.

Purcell's method, developed in 1946, involved placing the sample between the poles of a small magnet controlled by radio signals. The magnet's field fluctuated at a frequency corresponding to the control radio waves. The small magnet was then placed in a much stronger non-fluctuating magnetic field. The strong constant field caused the nuclei in the sample to precess at a certain constant frequency. When the frequency of the weak field's fluctuation matched the precession frequency of the nuclei, the orientation of the nuclear spins abruptly changed, resulting in a easily detectable effect known as nuclear magnetic resonance (NMR). NMR allowed for the precise measurement of the precession frequency, which is identical to the frequency of the radio signals sent at the onset of NMR. With the precession frequency known, nuclear magnetic moments could be calculated with high precision.

Purcell's method did not cause any noticeable changes in the sample being studied and allowed for the calculation of magnetic moments with greater precision than almost any other experimental method. Additionally, once the atomic nucleus's magnetic moment was known, it could be used to measure the intensity of any magnetic field. This made NMR not only important for nuclear physicists but also a useful tool for chemistry and medicine, as it could be used to study the structure of molecules and diagnose medical conditions without harming living organisms.

Contributions to Astronomy and Teaching

In 1951, using NMR, Purcell discovered that interstellar hydrogen atoms emit electromagnetic radiation at a radio frequency corresponding to a wavelength of 21 centimeters. He realized the potential of this radiation as a unique observational window in astronomical research. While interstellar space was believed to contain vast clouds of hydrogen, it was not observable using optical methods because hydrogen does not emit light in space. In collaboration with Harold Ewen, Purcell built the first radio telescope designed to detect radiation at a wavelength of 21 centimeters. These radio telescopes allowed for the determination of the overall structure of our galaxy despite the obscuring clouds of galactic dust.

Purcell's application of his physical research methods to the fields of astronomy, chemistry, and medicine brought about a true revolution in these areas, extending far beyond the realm of initial scientific inquiries.

Honors and Retirement

Purcell and Bloch were awarded the Nobel Prize in Physics in 1952 "for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith." In his Nobel lecture, Purcell spoke of nuclear precession, saying, "To this day, the feeling of wonder and excitement has never left me that this almost imperceptible motion is present in all common things which surround us... I remember how, during the winter in our early experiments... snowflakes took on a new light. The drifts of snow that piled up against my door became heaps of protons quietly precessing in the earth's magnetic field. To see for a moment our world as an extraordinary set of diverse objects was the reward of the discoverer."

In 1958, Purcell became a professor of physics at Harvard University, where he remained until his retirement. He served as a scientific advisor (1957-1960) and a member of the President's Science Advisory Committee in the United States (1957-1960, 1962-1966). During this period, Purcell made significant contributions to improving the teaching of physics in American high schools and colleges. He was a member of the committee that revised physics curricula and played an active role in the development of an introductory physics course adapted in Berkeley, for which he authored the textbook "Electricity and Magnetism" (1965), widely recognized as a masterpiece. In 1980, Purcell became an honorary professor at Harvard University.

In 1937, Purcell, then working on his doctoral dissertation, married Betty S. Bassner. They had two sons. In his leisure time, Purcell enjoyed hiking, skiing, and visiting contemporary art museums. In addition to the Nobel Prize, he received the Oersted Medal from the American Association of Physics Teachers (1968) and the National Medal of Science from the National Science Foundation (1980). He was a member of the National Academy of Sciences, the American Academy of Arts and Sciences, the American Philosophical Society, and the American Physical Society, serving as the president of the latter in 1980. From 1950 to 1971, Purcell held the position of Senior Fellow of the Harvard Alumni Association. He was also awarded an honorary degree from Purdue University.