- Person
- Isidor Isaac Rabi
- Lived
- 1898–1988
- Field
- Physics
- From
- Polish-born American
The story
The deuteron, the nucleus of heavy hydrogen, is made of just one proton and one neutron, making it the simplest compound nucleus in nature. Its isotope, deuterium, had been discovered at Columbia University in 1931 by Harold Urey, who won the 1934 Nobel Prize in Chemistry for the work. Urey supplied Isidor Isaac Rabi's Molecular Beam Laboratory with heavy water and deuterium gas, and he also gave Rabi half of his prize money to fund the laboratory.
Rabi's group studied hydrogen at the suggestion of his colleague Jerrold Zacharias, who thought the simplest element would be easiest to understand. Even so, Otto Stern's group in Hamburg had found that hydrogen did not behave as theory predicted. Using their new magnetic resonance method, Rabi, Polykarp Kusch, Sidney Millman and Zacharias measured the magnetic moment of the proton at about 2.79 nuclear magnetons, nearly three times the value of 1 predicted by theory, and that of the deuteron at about 0.86. By subtracting one from the other they could infer the neutron's magnetic moment, which turned out to be non-zero and opposite in sign to the proton's.
The more precise measurements also showed curious irregularities. They led Rabi to suggest that the deuteron had an electric quadrupole moment, a discovery made in 1939 together with Zacharias and Norman Ramsey. It meant that the deuteron was not a perfect sphere, as had been assumed, but slightly elongated.
That finding mattered far beyond hydrogen. If the force holding a proton and neutron together pulled equally in all directions, the deuteron would be round. Its shape showed that the nuclear force is not a simple central force but has a tensor component that depends on the orientation of the particles' spins. Hans Bethe counted the discovery among the important events of the formative years of nuclear physics.
The tensor force is now a standard part of models of the atomic nucleus. Nuclear quadrupole moments like the one Rabi's group first detected also show up in nuclear magnetic resonance, the technique that grew out of their laboratory and is now used throughout chemistry and medicine.
Why it matters
The finding helped physicists build accurate models of the atomic nucleus, the basis of nuclear energy and nuclear medicine.
About Isidor Isaac Rabi
Galician-born physicist who discovered nuclear magnetic resonance in molecular beams, won the 1944 Nobel Prize, and helped found Brookhaven and CERN, the root of today’s MRI and atomic clocks.
More about Isidor Isaac Rabi
- Rabi helped found Brookhaven National LaboratoryIsidor Isaac Rabi and Norman Ramsey rallied nine universities to found Brookhaven National Laboratory on Long Island, established in 1947.
- Rabi helped create the President's science advisersAfter Sputnik in 1957, Isidor Isaac Rabi's advice to President Eisenhower helped create the President's Science Advisory Committee.
- I. I. Rabi discovered how to make atomic nuclei 'ring'In 1937 Isidor Isaac Rabi's Columbia team invented the molecular-beam magnetic resonance method, winning him the 1944 Nobel Prize in Physics.
- Rabi led research on wartime microwave radarAt MIT's Radiation Laboratory during the Second World War, Isidor Isaac Rabi led research that pushed radar to sharper 3-centimetre wavelengths.
- I. I. Rabi opposed the hydrogen bomb on moral groundsIn 1949 Isidor Isaac Rabi joined Enrico Fermi on the AEC's advisory committee in opposing the hydrogen bomb on moral as well as technical grounds.
- I. I. Rabi planted the idea that became CERNAt a UNESCO meeting in Florence in June 1950, Isidor Isaac Rabi called for regional laboratories to rebuild European science; in 1952 European nations created CERN’s provisional council.
- I. I. Rabi proposed the atomic clock in 1945In a 1945 lecture Isidor Isaac Rabi proposed using the magnetic resonance of atoms to keep time; his colleagues soon built the first atomic clocks.
- Rabi's discovery is the root of the MRI scannerIsidor Isaac Rabi's magnetic resonance research led to MRI; in his final illness he was examined in a scanner descended from his own experiments.
Sources
- Isidor Isaac Rabi Wikipedia
- Nuclear force Wikipedia
- Norman Foster Ramsey Jr. Wikipedia
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