Obituary: Professor Wolfgang Paul

Wolfgang Paul, nuclear physicist: born Lorenzkirch, Saxony 10 August 1913; Director of Nuclear Physics Research, University of Bonn 1952-81; Director, Physics Division, Cern 1964-67, Delegate to Council 1975-78, Chairman, Scientific Policy Committee 1975-78; President, Alexander von Humboldt Foundation 1979-89; Nobel Prize for Physics 1989; married 1940 Liselotte Hirsche (died 1977; two sons, two daughters), 1979 Doris Waloh; died Bonn 7 December 1993.

WOLFGANG PAUL, probably the outstanding German nuclear physicist of the post-war era, died in Bonn on Tuesday shortly after a public celebration of his 80th birthday. With his death, not only Germany but all Europe has lost a grand old man of science, whose advice was sought and respected in very broad circles. He was a man of sterling character and of broad liberal views based on a deeply humanistic upbringing, and one of the few German physicists of his generation with impeccable credentials for dealing with his European colleagues after the Second World War.

Paul was trained at the Munich and Berlin Institutes of Technology, and obtained his MS in 1937 with Hans Geiger (of Geiger- counter fame) as examiner. In Berlin he became closely associated with the distinguished spectroscopist Hans Kopfermann, whom he followed first to Kiel (where he got his doctorate in 1939) and later to Gottingen. Kopfermann and the theoretical physicist Richard Becker exerted a deep and lasting influence on Paul's thinking throughout the troubled years of Nazi Germany; both men were non- Nazis, and Paul took no part in war- directed projects such as the German atom-bomb research. In Gottingen, Paul became involved with those experimental topics to which he was later to make fundamental contributions: molecular beam spectroscopy, mass spectrometry and electron acceleration.

In 1952, Paul was appointed as professor and director of the Physics Institute at the University of Bonn, a post that he occupied until his retirement in 1981. Bonn became under his leadership a fertile centre of experimental physics. It is in that laboratory that Paul and his co- workers developed the sextupole focusing of molecular beams, the radio-frequency (RF) quadrupole mass spectrometer and the RF ion trap (1955). That mass spectrometer possesses unprecedented mass resolution and has found wide application in silence and technology. The ion trap, the 'Paul trap', especially when used to store single ions, allowed physicists to hold elementary parts of matter long enough to study and precisely measure values, thus opening up whole new areas of physics. It is for this contribution that Paul was awarded, jointly with the American scientists Norman Ramsey and Hans Dehmelt, the 1989 Nobel Prize in physics.

Accelerator physics was also actively pursued in Bonn. Paul and his associates built two electron accelerators: a 500-MeV electron synchrotron, the first strong-focusing one in Europe; and in 1965 the 2.5-GeV machine. Paul's experience in this area had many fruitful ramifications. In 1957 he helped found, together with W. Jentschke and W. Walcher, the famous DESY laboratory in Hamburg. Paul was, in 1964-67, director of the nuclear physics division of Cern, the joint European laboratory for particle research in Geneva, a member and later chairman of its Scientific Policy Committee, and German scientific delegate Cern's council.

Wolfgang Paul was a member of several academies and received many honours and distinctions, including the Ordre pour le Merite and the Grand Cross with Star of Germany. He is survived by his second wife, Doris, a professor of medieval literature, two daughters and two sons, the latter both physicists - with whom he had collaborated on neutron storage experiments.

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