Willis Lamb Physicist who discovered the fine structure of the hydrogen spectrum Date of Birth: 12.07.1913 Country: USA

Biography of Willis Lamb

American physicist Willis Eugene Lamb was born in Los Angeles, California. His father and namesake was a telephone engineer, and his mother Marie Helen (Metcalf) Lamb was a teacher. Lamb attended elementary schools in Oakland and Los Angeles. He graduated from the Los Angeles High School, where he showed remarkable abilities in chemistry. He obtained a Bachelor of Science degree in chemistry from the University of California, Berkeley in 1934 and stayed there to work on his dissertation under the guidance of J. Robert Oppenheimer, for which he was awarded a doctoral degree in 1938. His dissertation focused on the electromagnetic properties of nuclear particles, predicting that the electric field of a proton should slightly differ from that of a point-like particle, such as an electron. Throughout his scientific career, Lamb taught physics at various universities, including Columbia University (1938-1951), Stanford University (1951-1956), Harvard University (1953-1954), University of Oxford (1956-1962), and Yale University (1962-1974). In 1974, he was appointed a professor of physics and optics at the University of Arizona. His dedication to his teaching duties was evident when he learned about being awarded the Nobel Prize. Lamb proceeded to give a seminar on quantum mechanics before meeting with the press.
From 1942 to 1952, Lamb worked part-time at the Radiation Laboratory of Columbia University on projects funded by the United States Army Signal Corps, the Office of Naval Research, and the Department of Scientific Research and Inventions. His work mainly focused on radar and microwave technology. Collaborating with I.A. Radie and a group working on molecular beams, Lamb became interested in the metastable states of atoms. Usually, an excited state of an atom quickly decays and the atom emits radiation, transitioning to a lower energy state. The most highly excited states decay by emitting a single photon, or light quantum, in approximately 10^-8 seconds. Metastable states, however, exist much longer. For example, the lifetime of the second excited state of a hydrogen atom is approximately 700 million times longer than that of other excited states. The reason for this "longevity" is that an atom in the second excited state cannot emit a single photon. Conservation laws of angular momentum and a property called parity require the atom to simultaneously emit two photons. This process is less probable and therefore occurs much more slowly.
Initially, Lamb was a theoretical physicist, but his most famous work is associated with a series of incredibly precise experiments, most of which were conducted in collaboration with Robert C. Retherford at Columbia University. As his research expanded during the war years, Lamb became intrigued by the absorption and emission of microwave radiation by atoms. Knowing from literature about unsuccessful attempts in the 1930s to detect microwave absorption in a gas consisting of excited hydrogen atoms, Lamb initially attributed the failure to inadequate microwave techniques. However, he later concluded that the chosen method for exciting the atoms hindered the detection. Lamb decided to employ improved microwave techniques to refine spectroscopic measurements of different energy levels of the hydrogen atom. In a hydrogen atom, a single electron orbits the nucleus on one of a series of levels. While on its orbit, the electron has a specific energy. To move to a higher orbit, the atom must absorb a photon whose energy precisely matches the energy difference between the orbits. The same occurs when the electron transitions to a lower orbit – the atom must emit a photon with the corresponding energy. These transitions produce the spectrum of atomic hydrogen, consisting of distinct and sharp lines.
Many lines in the hydrogen spectrum exhibit "fine structure." Under higher magnification, it becomes apparent that these lines consist of two or more closely spaced lines. This indicates that the orbital energy levels are also split into closely spaced sublevels. Transitions between neighboring sublevels of the fine structure require absorption or emission of radiation in the microwave range of wavelengths. In 1928, British physicist Paul A. M. Dirac derived an equation that described all the known properties of the electron: its wave properties, electric charge, spin, magnetic moment, and relativistic dependence of mass on velocity. Serving as the foundation of much of quantum mechanics, Dirac's equation accurately predicted the energy levels of the hydrogen atom. Specifically, the equation implied the equivalence of two special levels, one of which was metastable. These levels corresponded to different states but had the same energy. Lamb prepared a beam of hydrogen atoms in the metastable state, which lasted long enough for convenient experimentation. He then exposed the beam to microwave radiation in an external magnetic field. Some atoms absorbed the radiation and transitioned to a short-lived state. This meant that the two corresponding energy levels were not identical but separated by a small energy difference, which became known as the Lamb shift. Lamb's discovery prompted Julian S. Schwinger, Shin'ichiro Tomonaga, and Richard Feynman to revise Dirac's electron theory and formulate a new theory called quantum electrodynamics, which accurately predicted the Lamb shift. In collaboration with Norman M. Kroll, Lamb theoretically calculated the effect he had experimentally discovered.
Lamb was awarded the Nobel Prize in Physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum." He shared the prize with Polykarp Kusch, who independently performed similar experiments, also at Columbia University. Addressing the two laureates in his welcome speech, Ivar Waller of the Royal Swedish Academy said, "Your discoveries have led to a reassessment and reformulation of the theory of electron-electromagnetic interaction, quantum electrodynamics, thereby initiating a new stage of development that has been of primary importance to many fundamental concepts of physics." Over his many years of scientific research, Lamb worked in various areas of physics. He investigated topics such as beta decay theories, range of fission fragment projectiles, fluctuations in cosmic ray showers, emission of electrons by metastable atoms, field theories of nuclear structure, neutron-matter interaction theories, and the theory and design of magnetron generators, as well as diamagnetic corrections in nuclear resonance experiments. He made significant contributions to the development of laser theory as well.
Since 1939, Lamb has been married to Ursula Schaefer, a historian. In his leisure time, he enjoys swimming, sailing, chess, and photography. Lamb is a member of the National Academy of Sciences of the United States, the American Physical Society, an honorary fellow of the Institute of Physics in London, and the Royal Society of Edinburgh. Among the awards he has received are the Rumford Medal of the American Academy of Arts and Sciences (1953) and the Research Corporation Award for Scientific Merit (1955). Lamb holds honorary doctorates from the University of Pennsylvania, Yeshiva University, and Gustavus Adolphus College.