Vapour pressure changes in spin-polarised liquid He-3 and He-3-He-4 mixtures
Résumé
We prepare spin-polarised samples of liquid He-3 and He-3-He-4 mixtures by fast liquefaction of a vapour highly polarised by laser optical pumping. Nuclear polarisations of order 25% are routinely obtained in the liquid. We perform temperature and pressure measurements and induce sudden polarisation changes by pulsed NMR. Heat is expected to be released when the polarisation is reduced, and the saturated vapour pressure is expected to be lower for an unpolarised liquid at fixed temperature. In this experiment, the liquid is weakly coupled to a 0.5 K heat sink in order to successively observe both effects of polarisation changes. We report the first observation of these effects when the polarisation is suddenly destroyed in a liquid mixture (x=10%). In pure He-3, the observed saturated vapour pressure changes systematically differ from those expected. (C) 2000 Elsevier Science B.V. All rights reserved.