NMR measurements of hyperpolarized 3He gas diffusion in high porosity silica aerogels

Abstract

Hyperpolarized 3He is used to nondestructively probe by NMR the structure of custom-made and commercial silica aerogels (97% and 98.5% porous). Large spin-echo signals are obtained at room temperature and very low magnetic field (2mT) even with small mounts of gas. Attenuation induced by applied field gradients results from the combined effects of gas diffusion and confinement by the porous medium on atomic motion. Nitrogen is used as a buffer gas to reach equivalent 3He pressures ranging from 5 mbars to 3.5 bars. The observed pressure dependence suggests a non-uniform structure of the aerogels on length scales up to tens of micrometers. A description by broad phenomenological distributions of mean free paths is proposed, and quantitatively discussed by comparison to numerical calculations. The investigated aerogel samples exhibit different effective diffusion characteristics despite comparable nominal porosities.

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• In-Vivo NMR of Hyperpolarized Helium-3 in the Human Lung at Very Low Magnetic Fields
• Simultaneous Measurement of Rock Permeability and Effective Porosity using Laser-Polarized Noble Gas NMR
• Model of Inhomogeneous Impurity Distribution in Fermi Superfluids
• New universality class for the three-dimensional XY model with correlated impurities: Application to ${}^4$He in aerogels

Cited by in corpus (3)

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