Vapour pressure changes in spin-polarised liquid He-3 and He-3-He-4 mixtures

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. Nu clear polarisations of order 25% are routinely obtained in the liquid. We p erform temperature and pressure measurements and induce sudden polarisation changes by pulsed NMR. Heat is expected to be released when the polarisati on is reduced, and the saturated vapour pressure is expected to be lower fo r an unpolarised liquid at fixed temperature. In this experiment, the liqui d is weakly coupled to a 0.5 K heat sink in order to successively observe b oth effects of polarisation changes. We report the first observation of the se effects when the polarisation is suddenly destroyed in a liquid mixture (x=10%). In pure He-3, the observed saturated vapour pressure changes syste matically differ from those expected. (C) 2000 Elsevier Science B.V. All ri ghts reserved.