Paramagnetic relaxation of spin polarized 3He at bare glass surfaces |
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Authors: | J Schmiedeskamp W Heil E W Otten R K Kremer A Simon J Zimmer |
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Institution: | 1. Institut für Physik, 55099, Mainz, Germany 2. Max-Planck-Institut für Festk?rperforschung, 70569, Stuttgart, Germany 3. Schott AG, Mainz, Germany
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Abstract: | In this first in a series of three papers on wall relaxation of spin
polarized, gaseous 3He we investigate both by theory and by experiment
surface-induced spin relaxation due to paramagnetic sites in the containing
glass. We present experimental and theoretical evidence that — contrary to
the traditional opinion — distant dipolar coupling to paramagnetic
impurities in the glass, in particular iron ions, cannot be the dominant
relaxation mechanism of 3He-spins, although iron dominates the bulk
static permeability. Instead dangling-bond type defects in the glass matrix
are found to interact much stronger via the isotropic Fermi contact
interaction. A model of paramagnetic site controlled 3He relaxation
including the Fermi contact interaction is presented. With reasonable
semi-empirical assumptions our model allows to describe satisfactorily the
measured relaxivities, both in the dissolution-dominated regime of fused
silica or borosilicate glasses of the Pyrex type as well as in the surface
dominated situation of aluminosilicate glasses which have only a low
permeability for He atoms. In a large sample of 1.1 litre cells, built from
various aluminosilicate glasses, an average relaxation time of 150 h is
reached in case contaminant ferromagnetic particles have been demagnetized
beforehand. From the maximum observed value of 250 h we derive after
subtraction of dipolar relaxation in the gas phase a paramagnetic surface
relaxivity of ρ<0.005 cm/h at room temperature. |
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Keywords: | 33 25 +k Nuclear resonance and relaxation 34 50 Dy Interactions of atoms and molecules with surfaces photon and electron emission neutralization of ions 67 65 +z Spin-polarized hydrogen and helium |
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