Browsing by Author "Schwettman, Harry Alan"

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    I. Measurements on the nuclear magnetism in liquid HE_. II. A HE_ cryostat for nuclear magnetic resonance measurements
    (1960) Schwettman, Harry Alan; Rorschach, Harold E., Jr.
    The technique of adiabatic fast passage has been used to measure the nuclear susceptibility of liquid He3. Measurements along the vaporization curve from 1.2°K to 2.1°K indicate that anti-parallel alignment of the He3 spin system in this temperature range is more important than suggested by previous measurements. Unless existing data at temperatures below 1°K are incorrect, it appears that the susceptibility of He3 is not given precisely by the ideal Fermi-Dirac expression. A He3 cryostat has been constructed to extend the measurements to lower temperatures. Both the operating characteristics of a preliminary cryostat and the design of the final cryostat are discussed.
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    Nuclear paramagnetism of helium three
    (1962) Schwettman, Harry Alan
    The technique of adiabatic fast passage has been employed to measure within +/-1% the susceptibility of pure He3 and some He3--He4 mixtures for temperatures between 0.9°K and 3.0°K. Above 1.2°K the susceptibility varies as the inverse of the temperature, indicating that the statistical and exchange correction to the Curie susceptibility is very nearly constant. We have calculated the magnetization of an interacting system of He 3 particles near the classical limit. Plane waves have been used to evaluate the potential energy and the exchange energy of the particles. In this approximation potential correlation is handled by the introduction of a cutoff radius a. For reasonable choices of the cutoff, the statistical correction and the exchange correction are of comparable magnitude.