Dehmelt, Hans Georg (1922-2017), was a German-born American physicist who developed ways of trapping electrons, ions, and atoms for scientific study. Dehmelt shared half of the 1989 Nobel Prize for physics with Wolfgang Paul, who independently developed an ion trap technique. The other half of the prize went to Norman F. Ramsey for work in a different field. In 1995, Dehmelt and his team at the University of Washington captured a kilo-e, a spherical drop of 1,000 electrons, in an atom trap. The team could then measure disturbances that were too small to be measured in a single electron.
Dehmelt was born on Sept. 9, 1922, in Gorlitz, Germany. During World War II (1939-1945), he served in an antiaircraft unit and was captured in the Battle of the Bulge in 1944. After his release in 1946, he began studying physics under Wolfgang Paul at Gottingen University, receiving his doctorate in 1950.
As a doctoral student Dehmelt worked on mass spectrography, a technique of using electric and magnetic fields to separate a beam of particles according to their masses. Later, he studied nuclear magnetic resonance (NMR), the interaction of atomic nuclei with an external magnetic field when various radiation frequencies are applied.
Dehmelt discovered a related form of magnetic interaction called nuclear quadrupole resonance, (NQR) in 1949. He was invited to join the faculty at Duke University in North Carolina in 1952 and worked there until 1955. He then accepted a position atthe University of Washington in Seattle becoming a full professor in 1961. In the same year, he became a U.S. citizen.
Dehmelt developed ways of capturing free electrons and ions, using electric and magnetic fields. An electron is a subatomic particle carrying one unit of negative electric charge. All atoms have electrons moving around a nucleus. An ion is an atom or group of atoms having a negative or positive electric charge as a result of having lost or gained one or more electrons. Dehmelt could keep the electrons or ions trapped for about 10 seconds, ample time in which to study their properties. In 1973, he became the first scientist to isolate a single electron. He and his collaborators went on to achieve the same feat with various ions and with positrons, the first antiparticles to be discovered. A positron has a mass equal to that of the negatively charged electron, but its electrical charge is positive. In 1976, Dehmelt devised a means of cooling a single electron in a trap, and thus improved the accuracy of his measurements. By this time, he could trap ions for up to months at a time. Apart from its value in the study of the properties of atoms and electrons, the ion-trap technique can be applied to extremely accurate timekeeping. Dehmelt died on March 7, 2017.
