Edward Mills Purcell

(b. 1912)

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Felix Bloch (1905—1983)


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(1912–) American physicist

Purcell was born at Taylorville, Illinois. He gained his BSc degree in electrical engineering at Purdue University, Illinois (1933) and his masters degree and PhD from Harvard (1938), having also spent a year in Germany at the Technische Hochschule, Karlsruhe. At Harvard his career advanced from instructor in physics (1938), to associate professor (1946), full professor (1949), and professor emeritus (1980). During the war years 1941–45 he was a group leader at the Massachusetts Institute of Technology Radiation Laboratories.

Purcell's research has spanned nuclear magnetism, radio astronomy, radar, astrophysics, and biophysics. In the field of nuclear magnetism, he was awarded the 1952 Nobel Prize for physics (shared with Felix Bloch) for his work in developing the nuclear magnetic resonance (NMR) method of measuring the magnetic fields of the nuclei of atoms. As a result of these experiments, measurements of nuclear magnetic moment could now be performed on solids and liquids, whereas previously they had been confined to molecular beams of gases. Nuclear magnetic resonance is now commonly applied in chemical analysis.

Purcell's major contribution to astronomy was the first detection of microwave emission from neutral hydrogen in interstellar space at the wavelength of 21 centimeters (1420 Hz). The phenomenon had been predicted theoretically by Hendrik van de Hulst and others and was first observed in 1951 by three independent groups of radio astronomers – American, Dutch, and Australian – the American group being the first to report their findings. This, and the subsequent observation of the corresponding absorption line by the Dutch group in 1954, has made possible the mapping of a large part of our own galaxy, and allowed the calculation of the excitation temperature in interstellar space. Purcell was also aware of the possible future implications of his discovery for interstellar communications.

Subjects: Science and Mathematics.

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