Thermometry Based on the Melting Line of 3He
Few types of thermometry are available below 1 K, and none is sufficiently well established, readily available, or widely used in laboratories around the world. As discussed in the preceding chapters, even the ITS-90 below 1 K is affected by the degradation of the experimental data forming its basis. As far as the use of gases is concerned, the choice is restricted to 3He. In both vapor-pressure thermometry and gas thermometry, increasing experimental difficulties are encountered below 1,000 mK. In no way, can these techniques be applied much below 500 mK.