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Paramagnetic relaxation of spin polarized 3He at bare glass surfaces – Part I

MPS-Authors
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Kremer,  R. K.
Former Scientific Facilities, Max Planck Institute for Solid State Research, Max Planck Society;

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Simon,  A.
Former Departments, Max Planck Institute for Solid State Research, Max Planck Society;

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Citation

Schmiedeskamp, J., Heil, W., Otten, E. W., Kremer, R. K., Simon, A., & Zimmer, J. (2006). Paramagnetic relaxation of spin polarized 3He at bare glass surfaces – Part I. European Physical Journal D, 38(3), 427-438.


Cite as: https://hdl.handle.net/21.11116/0000-000F-02A7-2
Abstract
In this first in a series of three papers on wall relaxation of spin
polarized, gaseous He-3 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 He-3-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 He-3 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 rho < 0.005 cm/h at room temperature.