HEAT RELEASE, REFRIGERATION AND THERMOMETRY IN HE-3-HE-4 SOLUTIONS ATVERY-LOW TEMPERATURES

We report on our measurements performed in liquid He-3-He-4 solutions in the microkelvin temperature range at the Bayreuth nuclear demagneti zation cryostat. One aspect of our work is the application of the vibr ating wire technique for thermometry in the ballistic regime of phase- separated solutions. The establishment of reliable thermometry along w ith the particular design of our experimental cells enables us to stud y two main limitations on the minimum temperature of about 100 mu K ac hieved in He-3-He-4 solutions so far: the thermal resistance between t he liquid and the cell, and the origins of the heat leaks.