Nobel Prize-winning physicist whose input led to finely tuned atomic clock

From the Irish Times: Nobel Prize-winning physicist whose input led to finely tuned atomic clock
NORMAN F RAMSEY: NORMAN F RAMSEY, the Nobel Prize-winning physicist who developed a precise method to probe the structure of atoms and molecules and used it to devise a remarkably exact way to keep time, died in Wayland, Massachusetts, aged 96.

In 1949, Ramsey invented an experimental technique to measure the frequencies of electromagnetic radiation most readily absorbed by atoms and molecules. The technique allowed scientists to investigate their structure with greater accuracy and enabled the development of a new kind of timekeeping device known as the atomic clock. Ramsey received the Nobel Prize for physics in 1989 for both achievements.

“If you made a list of the most outstanding physicists of the 20th century, he’d be among the leaders,” said Leon M Lederman, emeritus director of the Fermi National Accelerator Laboratory in Batavia, Illinois, which Ramsey helped found. Early in the 20th century, physicists began to decipher the structure of atoms from measurements of the wavelengths of light they released and absorbed, a method called atomic spectroscopy. In 1937, the physicist Isidor Isaac Rabi of Columbia University developed a means of studying atoms and molecules by sending a stream of them through rapidly alternating magnetic fields. As Rabi’s student at Columbia in the late 1930s, Ramsey worked to refine it.

In 1949, when he was at Harvard, Ramsey discovered a way to improve the technique’s accuracy: exposing the atoms and molecules to the magnetic fields only briefly as they entered and left the apparatus. His approach – often referred to as the Ramsey method – is widely used today.

Ramsey’s research helped lay the groundwork for nuclear magnetic resonance, whose applications include the MRI technique now widely used for medical diagnosis. But the most immediate application of the Ramsey method has been in the development of highly accurate atomic clocks. Since 1967 it has been used to define the exact span of a second, not as a fraction of the time it takes Earth to revolve around the sun, but as 9,192,631,770 radiation cycles of a caesium atom.

In 1960, working with his student Daniel Kleppner, now an emeritus professor of physics at the Massachusetts Institute of Technology, Ramsey invented a different type of atomic clock, known as the hydrogen maser, whose remarkable stability has since been used to confirm the minute effects of gravity on time as predicted by Einstein’s theory of general relativity. Atomic clocks like the hydrogen maser are also used in the systems that track global positioning satellites.

Norman Foster Ramsey jnr was born on August 27th, 1915, in Washington, the son of Minna Bauer Ramsey, a mathematics teacher, and Norman Foster Ramsey, an army officer. After receiving his PhD under Rabi at Columbia, he worked at the MIT Radiation Laboratory and served as a radar consultant to the secretary of war. In 1943 he went to New Mexico to work on the Manhattan Project, leading a team that helped assemble the bombs dropped on Hiroshima and Nagasaki, Japan. After the war, he taught for nearly four decades at Harvard. Although he officially retired in 1986 he continued his work and in recent years he collaborated with British physicists on the symmetry of the neutron.

Ramsey presided over the founding of Fermilab and the Brookhaven National Laboratory on Long Island, where he was the first head of the physics department in the 1940s. As the first science adviser to Nato, he initiated programmes to train European scientists. He led a committee that concluded in 1982 that, contrary to the findings of the House Select Committee on Assassinations, acoustical evidence did not support the existence of a second gunman in the assassination of John F Kennedy.

Ramsey had an athletic flair. He learned to ski in Norway in the 1930s. Later, he took up long-board surfing and ice sailing, and he travelled with his second wife, Ellie Welch Ramsey, from the Himalayas to Antarctica.

His first wife, Elinor, died in 1983. In addition to his wife, he is survived by four daughters, Margaret Kasschau, Patricia Ramsey, Winifred Swarr and Janet Farrell; two stepchildren, Marguerite and Gerard Welch; eight grandchildren; and nine great-grandchildren.