OBSERVATION OF HE-3 CRYSTAL NUCLEATION FROM THE SUPERFLUID PHASES

A CCD camera operating at T = 65 K was mounted in the vacuum space of our nuclear demagnetization cryostat. This has allowed us to make obse rvation ns of He-3 crystals at temperatures below the superfluid phase transitions, in contrast to direct optical observations, which have s o far been limited to T greater than or equal to 20 mK.(1) The good th ermal equilibrium provided by the superfluid allows us to nucleate sin gle crystals of He-3 in the region of the cell visible to the optical system. This occurs either spontaneously (due either to gravitational pressure gradients or focal surface defects) or as a result of a small applied heat pulse.