Purcell (Purcell), Edward M.

American physicist Edward Purcell was born in Milo, Mr.. Teylorville (Illinois), the son of Edward A. Purcell and Mary Elizabeth (nee Mile) Purcell. Primary and secondary education in public schools and Teylorvillya Mattuna. In 1929, Mr.. P. goes to Purdue University in g. Lafayette (Indiana). By the time of obtaining a bachelor's degree in electrical engineering (1933), he takes an interest in physics. After a year of exchange students at the Technical University of Karlsruhe (Germany), P. goes to graduate school in physics at Harvard University where he received a master's degree (1936) and Ph.D. (1938). Until 1940. He remained at Harvard as a teacher.
During World War II. passes in a radar lab at MIT, created for the development of microwave radar. There he leads a group of Fundamental Research (1941 ... 1945), involved in the development of new techniques for generating and detecting microwaves (high frequency electromagnetic radiation). During this period he also comes in contact with IA. Rabi, who was then studying the properties of atoms and molecules using radio waves. In 1946, Mr.. P. returned to Harvard as an associate professor of physics and in 1949. becomes full (real) Professor. Knowledge of the properties of microwave radiation and radio frequency ranges obtained in the development of radar systems, have helped P. in his Harvard study of magnetic moments of nuclei, which subsequently earned him the Nobel Prize.
Since 20-ies. was known that the nucleus rotates around its own axis and acts as a tiny magnet. Precise knowledge of the magnetic moments (forces of magnets) of various nuclei is important for physicists trying to understand the behavior of the kernel. In particular, physicists need to know the magnetic moment of the proton (a fundamental component of the kernel). In 30-ies. Rabi proposed a method of measuring magnetic moments with the help of radio waves, but his method required the evaporation of the sample. P. set out to develop a method that not only would destroy the sample, but also superior to the accuracy of the Rabi method. Around the same time, Felix Bloch of Stanford University (also participated in the war years in the establishment and improvement of radar technology) began work on the same problem. At the same time and independently of each other, two researchers have proposed essentially the same methods of measuring nuclear magnetic moments.
Magnetic moment forcing the core to precess in a magnetic field. Precession - a circular movement of the inclined axis of a rotating object. A famous example is the rocking motion of the rotating top (although the precession of a gyroscope is under the influence of gravity, not magnetism). Frequency, or speed, nuclear precession depends on the magnetic field and the magnetic moment of a particular nucleus. If you know the external magnetic field, and the precession frequency is measured, the magnetic moment of the nucleus can be calculated. The method developed by P. in 1946, consisted in the fact that the sample is placed between the poles of a small magnet is activated by the radio signals. Field of the magnet fluctuate (turn on and off) with a frequency corresponding to the frequency control of radio waves. In turn, this small magnet placed in a far more intensive field of a large magnet nefluktuiruyuschego. The strong field causes the constant kernel in the sample precess with a constant (but unknown) frequency. When the frequency of the fluctuations of a weak field coincides exactly with the frequency of precession of nuclei, nuclear spin orientation changes abruptly to the opposite: There is a readily detectable effect, called nuclear magnetic resonance (NMR). NMR can accurately measure the precession frequency: it coincides with the frequency of radio signals sent at the time of the NMR. But as soon as the precession frequency of nuclei in the sample is known, the nuclear magnetic moments can be calculated with an equally high accuracy.
. Purcell's method does not lead to any tangible changes in the analyte, and allows us to calculate the magnetic moments more than almost any other experimental method, accuracy
. In addition, since the magnetic moment of the atomic nucleus is defined, it can be used to measure the intensity of any magnetic field. Thus, in addition to information essential for a specialist in nuclear physics, NMR provides a convenient and precise method for measuring the magnetism with the help of radio waves.
P NMR P. found that the behavior of the magnetic moments of nuclei in a molecule affect the magnetic field surrounding the electron. While physicists, . attempting to determine the properties of the kernel, . Such effects may seem annoying subtleties, . intrinsic molecules, . Chemists have found them very important and useful, . because these effects contain important information about the structure of the molecules studied,
. MRI has quickly become one of the most powerful analytical tools of chemistry. In addition, NMR measurements can be used in the study of living organisms, since the latter do not cause any harm. Appeared in 70-ies. scanners on the basis of NMR can monitor specific chemical reactions that occur in humans or other large mammals. The extremely useful in research, MRI scanners have been a convenient tool for medical diagnostics. In the mid 80's. medical domain has been producing industrial scanning diagnostic equipment on the basis of NMR.
In 1951, Mr.. P. using NMR revealed that the interstellar hydrogen atoms emit electromagnetic radiation at radio frequencies, corresponding to a wavelength equal to 21 cm. He quickly realized that this radiation can serve as a kind of observation window in astronomical research. It was believed that interstellar space contains a huge cloud of hydrogen, but because the hydrogen in outer space does not emit light, it is not seen by optical methods. P. in collaboration with Harold Dzhyuenom managed to build the first radio telescope designed to detect radiation with a wavelength equal to 21 cm. Then, radio telescopes have allowed to determine the overall structure of our Galaxy, despite the obscure clouds of galactic dust.
Application of methods developed by P. for physics research, . to address the problems of astronomy, . chemistry and medicine, . caused a real revolution in these areas, . was an outstanding example of, . how basic research can lead to practical results, . lying far beyond the field of initial searches.,
. P
. Felix Bloch was awarded the Nobel Prize in Physics 1952. 'for the creation of new methods for nuclear magnetic precision measurements and the associated opening'. In his Nobel lecture P. said about the nuclear precession: 'I was and still is not leaving a sense of wonder and delight at the fact that it is a subtle movement is present in all the ordinary things that surround us ... I remember in the winter during our first experiments ... snowflakes seen me in a completely new light. Snow drifts, lying at my door, stood before me like heaps of protons quietly precessing in the earth's magnetic field. See for an instant, our world as something extraordinarily diverse and unusual - this is a reward for its discoverer discovery '.
In 1958, Mr.. P. became professor of physics at Harvard, where he remained until retirement. He was appointed Scientific Advisor (1957 ... 1960) and a member of the Presidential Scientific Advisory Committee of the United States (1957 ... 1960 1962 ... 1966). During this period, P. did much to improve the teaching of physics in American high schools and colleges, as a member of the commission is responsible for reviewing programs in Physics and a member of the Committee on the situation in physical science. He took an active part in the development of an introductory course in physics, adapted in Berkeley, who wrote a textbook for the 'Electricity and magnetism' ( 'Electricity and Magnetism', 1965), admittedly, is a masterpiece. In 1980. P. became an honorary professor at Harvard University.
In 1937, Mr.. AP, while still working on his doctorate, he married Beth P. Bassner. They had two sons. In his leisure hours P. likes to make walking, skiing, visiting museums of modern art.
In addition to the Nobel Prize, P. was awarded the Oersted Medal of the American Association of Physics Teachers (1968) and the National Medal 'For his scientific achievements' of the National Science Foundation (1980). He is a member of the U.S. National Academy of Sciences, the American Academy of Arts and Sciences, the American Philosophical Society and the American Physical Society, whose president he was in 1980. From 1950 to 1971. P. was a senior member of the Society of Alumni of Harvard University. He was awarded the honorary degree at Purdue University.