Low temperature thermometry, 1 to 30 K

Abstract

The current interest and activity in thermometry between 4 and 20 K is due primarily to the development and subsequent commercial availability of 4-terminal germanium resistors as reproducible and sensitive thermometers. These have assumed the same role below 20 K as platinum resistance thermometers have above 20 K. Thermometric techniques in this low temperature region have evolved from insensitive alloy thermometers (such as constantan) to the use of high sensitivity (but sometimes irreproducible) carbon radio resistors to the introduction of the first suitably-doped germanium resistance thermometers by Kunzler and his co-workers at the Bell Telephone Laboratories.¹ Thermometers of this type now are manufactured by several different concerns and they are used routinely at temperatures from 0.1 to 40 or 50 K with mK sensitivity and reproducibility. These thermometers have brought about a considerable rethinking and simplification of cryogenic techniques; and, in many instances, they are used from 1 to 20 K (or higher) with calibrations which are certified by or traceable to Standards Laboratory scales, with little or no provision made for checks of the calibration by the user.