Calorimeter for the Liquid Helium

Abstract

We designed a calorimeter for the liquid helium and constructed it. The calorimeter has a needle valve assembly which operates at the liquid helium temperature. The needle valve assembly enables one to seal the sample cavity and evacuate the filling tube. This excludes next troubles; the large heat leak due to the superfluid film flow, the change of the ³He mole fraction and the amount of the sample during the experiment. When this calorimeter is isolated thermally, it can be kept at extremely constant temperature by controlling the temperature of the surrounding liquid helium bath. The drift rate of temperature was less than 1.7×10^-6K/hour. It corresponds to the heat leak of 0.5erg/min. This temperature stability and our temperature resolution. 1×10^-7K, enable one to perform heat capacity measurements very near T_λ (superfluid transition temperature), 3×10^-6K_??_|T-T_λ|<10^-2K.
The drift rates of resistivity at T_λ were also examined on a carbon thermometer (Allen-Bradley 1/8W 47Ω) and a germanium thermometer (Scientific Instruments model NI). The indication of a germanium thermometer was found to be constant within experimental errors, but that of a carbon thermometer varied markedly. After cooling a carbon thermometer and keeping it at T_λ±0.1K for 40 hours, the drift rate of its indication was reduced to about 6×10^-6K/hour.