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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. [ABSTRACT FROM AUTHOR]

In the first in a series of three papers on wall relaxation of spin polarized 3He we have reported on a breakdown of relaxation times which is observed after exposing the 3He containing glass cells to a strong magnetizing field. In this third paper we give a quantitative analysis of this phenomenon, based on magnetic signal detection by means of SQUIDs, on the pressure dependence of relaxation times in magnetized cells, as well as on Monte Carlo simulations of 3He-relaxation in a macroscopic dipole field. Our analysis allows to identify the contaminants as being aggregates of dust-like Fe3O4 particles (magnetite) with a radius $R \approx 10~\mu$ m and a remanent magnetic moment of the order of m ≈O(10 $^{-10}~$ A m2). The particles are located at or close to the inner glass surface. [ABSTRACT FROM AUTHOR]