From The NYTimes:
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 on Friday in Wayland, Mass. He was 96.
His death was confirmed by his wife, Ellie.
In 1949, Dr. 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. Dr. Ramsey received the Nobel Prize in Physics in 1989 for both achievements.
The Globe obit requires a subscription:
With one of his former students, Daniel Kleppner, Dr. Ramsey developed the hydrogen maser (microwave amplification by stimulated emission of radar), the most stable source of electromagnetic radiation. This led to "a clock of unprecedented stability,‘’ as Dr. Ramsey later put it: the atomic cesium clock, which is the present international time standard. By its measurement, one second equals the time required for an atom of cesium to oscillate 9,192,631,770 times… Kleppner, reached by phone yesterday, said Dr. Ramsey’s warmth of personality and high professional standards complemented his advanced research.
“He was one of the towering figures in the second half of the 20th century in physics,‘’ Kleppner said. "His ideas kind of permeate the field of atomic physics now. He always left a deep personal impression, which is one of the reasons why he is so widely appreciated in the field.’’