Eur. Phys. J. D 38, 427-438 (2006)
https://doi.org/10.1140/epjd/e2006-00050-2

Paramagnetic relaxation of spin polarized ³He at bare glass surfaces

Part I

¹ Institut für Physik, 55099 Mainz, Germany
² Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany
³ Schott AG, Mainz, Germany

Corresponding author: ^a wheil@mail.uni-mainz.de

Received: 26 August 2005
Revised: 19 December 2005
Published online: 14 March 2006

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.