The influence of small impurities of He-4 on the melting curve of He-3

The melting curve of He-3 containing a small He-4 impurity is measured in t he temperature range 20-600 mK. It is found that the coordinates of the min imum of the melting curve are shifted, that hysteresis appears, and that th e slope of the melting curve at low temperatures is changed. The data obtai ned agree with a calculation that takes into account the change in the coor dinates of the minimum due to the entropy of mixing of the He-3-He-4 soluti on. The results of the experiment are used to estimate the error arising wh en the melting curve of He-3 is used to determine the temperature. (C) 2001 American Institute of Physics.