Norman Ramsey obituary

Publié le par The Guardian - Anthony Tucker

The Guardianpublished 18/11/2011 at 16:23 GMT by Anthony Tucker

Nobel prizewinning physicist and designer of the delivery system for the first atomic bombs

Norman Ramsey
The brilliant American scientist Norman Ramsey, who has died aged 96, arrived in Britain as a postgraduate fellow in the mid-1930s to study under Lord (Ernest) Rutherford and Maurice Goldhaber at the Cavendish Laboratory in Cambridge. He went on to head the American development of short-wave radar, to become a key technical adviser to the US government and a world leader in the development of molecular beams and, ultimately, to win the 1989 Nobel prize in physics for developing the world's most accurate clock – the hydrogen maser.

Ramsey's technical grasp and range were enormous. His interest in molecular beams – unidirectional streams of neutral molecules that allow a detailed study of the characteristics of individual molecules – was stimulated at Cambridge by work he carried out for Goldhaber, his tutor. The upshot was that, on his graduation from Cambridge in 1937, he joined Isidor Isaac Rabi at Columbia University, where studies of molecular beams were being carried forward with vigour.

Shortly after Ramsey's arrival, Rabi invented molecular beam resonance spectroscopy, a technique of great elegance and importance for which he won the 1944 Nobel prize in physics. As Rabi's only graduate student, Ramsey had the good fortune to be part of the team that worked on the first experiments making use of the new technique, and to share in the discovery of a fundamental molecular characteristic – the deuteron quadrupole moment.

This discovery clinched the power of molecular spectroscopy and, almost before his thesis was complete, Ramsey was invited to Washington as a Carnegie Institution fellow to study molecular characteristics and particle interactions and scattering. By 1940, newly married to a fellow scientist, Elinor Jameson, Ramsey was looking forward to a lifelong shared career in peaceful academic research in a new post at the University of Illinois. The second world war determined otherwise. Ramsey was abruptly summoned to the Massachusetts Institute of Technology's radiation laboratory, which had been set up in late 1940 at the suggestion of Professor John Chadwick and Dr EG "Taffy" Bowen, to develop new radar systems based on the British cavity magnetron.

Ramsey headed a team whose aim was to miniaturise the highly secret eight-segment 10cm wavelength device – with which the UK Tizard mission had amazed American military scientists – in order to produce high-power ultra-short-wave (3cm) radar. Ramsey's team, of which Bowen was an occasional member, was quickly successful. His technical ability and powers of leadership were so striking that, although by 1943 he was back in Washington as a government adviser on the use of the 3cm radar sets coming into service, he was transferred to the Manhattan Project to serve as the chief scientist on the tiny Pacific island of Tinian.

In 1943 Tinian was being transformed into the platform for the final air assault on Japan. There, Ramsey completed the aerodynamic design and trajectory tests of the two types of atomic weapon eventually dropped on Japan. This required the modification of bomb bays for test dropping and integration of delivery systems. When he began this work the only aircraft with a bomb bay large enough to house the 27ft "gun barrel" of the uranium weapon ("Little Boy") was the British Lancaster, at that time being built in large numbers in Canada.

Although the B29 (Superfortress) would eventually deliver the weapons, the first fully equipped service version had crashed on its maiden flight and none was available. Ramsey promptly asked for a Lancaster. The American authorities, aghast at the idea of versions of the American superweapon being tailored into and dropped from a British aircraft, abruptly refused.

Ramsey therefore carried out all the essential tests from a smaller but available B19 (Fortress), using two-thirds scale models welded up from standard bomb cases, cast-iron pipes and other available ordnance material. On the first test drops the model of "Little Boy" – the uranium bomb – spun like a falling leaf and had to be substantially modified. For the Tinian tests, the "Little Boy" mock-up was called "Thin Man" which, coupled with "Fat Man" (the plutonium bomb), gave the impression that the aircraft were being modified to carry Roosevelt and Churchill. In the tests "Fat Man" presented few problems.

Ramsey's macabre work on A-bomb delivery was a triumph of empiricism quickly proven over Hiroshima and Nagasaki. If, after the war, Ramsey had profound misgivings about his Tinian years and involvement with A-bomb delivery, he never gave these voice. Instead he returned vigorously to academic life at Harvard where – except for visiting professorships at Oxford – he taught for 40 years. Over this time he led teams which developed high-energy accelerators, invented an improved molecular beam magnetic resonance system, made the molecular characteristic studies which underlie present-day magnetic resonance techniques for chemical analysis and medical imaging and, finally, invented the hydrogen maser, a time standard far more accurate than the caesium clock.

Essentially a vacuum cavity amplifier tuned to the frequency of molecular hydrogen allowed to pass slowly through it, this form of ultra-accurate clock was quickly brought into use to measure things such as the rate of continental drift, to synchronise the timebase of widely separated radio telescopes and, to Ramsey's special satisfaction, to verify aspects of quantum theory and the general theory of relativity.

Ramsey was a prodigy. Born in Washington, the son of a maths teacher, Minna, and a general in the US Army Ordnance Corps, also named Norman, he was expected to follow in his father's footsteps and to enter West Point military academy from high school. Instead, and in spite of his early school years being disrupted by family moves that followed his father's postings, he was able to skip several grades and he graduated with high academic honours when only 15. By then, stimulated by articles on quantum theory, he knew that his future lay in science, although he did not realise that physics and mathematics offered a career.

His school record was so outstanding that, as he approached graduation, he was offered an immediate scholarship to Kansas University. Before he could accept, however, his father was posted to New York City and the family moved again. Aged 16, he was granted a scholarship to Columbia College. Although he entered the engineering department – a choice which may well have pleased his father – he quickly realised not only that he sought greater depths of natural understanding than could be provided by engineering, but also that these could only be reached and interpreted through the language of mathematics and physics. His triumphs in maths at Columbia carried him to Cambridge and Harvard.

Ramsey was an educator, a man of deep culture, an amateur naturalist, a hill walker, a lover of music and a man possessing powerful gifts of persuasion. During 1959-60, when on secondment as science adviser to Nato, he initiated the Nato programme for advanced study institutes, fellowships and research grants, which continue to enrich fundamental science and cultural studies at universities throughout Europe and North America. His books include Nuclear Moments (1953), Molecular Beams (1956) and Quick Calculus (1965). He was a member of the International Council for Science, president of the American Physical Society and a campaigning member of the American Association for the Advancement of Science.

After Elinor died in 1983, he married Ellie Welch. In 1989, in his Nobel autobiography, he wrote proudly of their combined family and happily of his many students. "I hope," he wrote, "that they have learned as much from me as I have learned from them."

He is survived by Ellie; his daughters from his first marriage, Margaret, Patricia, Winifred and Janet; his stepchildren, Marguerite and Gerard; eight grandchildren; and nine great-grandchildren.

Norman Foster Ramsey, scientist, born 27 August 1915; died 4 November 2011

Anthony Tucker died in 1998

Publié dans Avis de décès

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