Skip to Main content Skip to Navigation
Theses

L'hélium-3 polarisé gazeux en-dessous d'un kelvin: orientation par pompage optique, relaxation sur une paroi recouverte d'hélium-4

Abstract : Optical pumping techniques, first developed by Colegrove, Schearer, Walters (Physical Review, 1963, vol. 132, p. 2561) make possible to get spin polarized samples of helium-three gas. In low magnetic fields is such a system off-equilibrium. Spin relaxation occurs mainly in the vicinity of the container walls. The atoms interact during their adsorption with magnetic impurities present near or inside the walls. The use of lowly attractive cryogenic solid coatings, like neon or molecular hydrogen, decreases the efficiency of this relaxation process. At a temperature lower than two Kelvin, the adsorption times become too long. We then added a helium-four film in the samples. It excludes helium-three atoms from the vicinity of the walls. With such a film, we obtained by optical pumping a few per cent of nuclear orientation at half a Kelvin. The value of the longitudinal relaxation time was more than thousand seconds. Variations of relaxation time with film thickness, coating composition, gas density and temperature have been studied experimentally. Increasing condensation of helium-four with lowering temperature, helium-three adsorption on the film, helium-three dissolution into the film, especially in the first layers, have been discussed in details. We got a few models describing relaxation processes occuring in the samples. Furthermore, we achieved the first measurements of the spin diffusion coefficient in gaseous helium below one Kelvin, using Nuclear Magnetic Resonance techniques for the detection of the free precession of the spins in calibrated magnetic field gradients.
Complete list of metadata

Cited literature [38 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-00011860
Contributor : Jacques Dupont-Roc <>
Submitted on : Thursday, March 9, 2006 - 8:42:22 AM
Last modification on : Friday, April 9, 2021 - 11:50:02 AM
Long-term archiving on: : Saturday, April 3, 2010 - 9:15:22 PM

Identifiers

  • HAL Id : tel-00011860, version 1

Citation

Marc Himbert. L'hélium-3 polarisé gazeux en-dessous d'un kelvin: orientation par pompage optique, relaxation sur une paroi recouverte d'hélium-4. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1987. Français. ⟨tel-00011860⟩

Share

Metrics

Record views

311

Files downloads

300