MPI für Festkörperforschung / FKF Publikationen 2006 |
|Paramagnetic relaxation of spin polarized 3He at bare glass surfaces – Part I|
|Authors:||Schmiedeskamp, J.; Heil, W.; Otten, E. W.; Kremer, R. K.; Simon, A.; Zimmer, J.|
|Date of Publication (YYYY-MM-DD):||2006|
|Title of Journal:||European Physical Journal D|
|Issue / Number:||3|
|Abstract / Description:||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.
|External Publication Status:||published|
|Communicated by:||N. N.|
|Affiliations:||MPI für Festkörperforschung|
|External Affiliations:||Univ Mainz, Inst Phys, D-55099 Mainz, Germany.
; Max Planck Inst Festkorperforsch, D-70569 Stuttgart, Germany.
; Schott AG Mainz, Mainz, Germany.
|Identifiers:||ISI:000237291600002 [ID No:1] |
ISSN:1434-6060 [ID No:2]
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