液氦超流转变温度复现性研究

利用液氦超流转变时超流氦（He Ⅱ）与正常氦（He Ⅰ）热导率突变的性质复现液氦超流转变温度T_λ。采用带毛细管结构的小型密封瓶，通过控温将微小热流通过小型密封瓶毛细管，实现毛细管中He Ⅰ/He Ⅱ两相共存，并使He Ⅰ/He Ⅱ界面停留在毛细管中，从而获得稳定、平坦的液氦超流转变温坪。利用毛细管热流对液氦超流转变温度的下压效应，得到不同热流的多个温坪，进一步利用外推法求得零热流下真实的T_λ值。24次液氦超流转变温度复现实验结果表明，标准偏差为0.022mK，证明了液氦超流转变温度具有良好的稳定性和复现性，推荐将液氦超流转变温度作为国际温标的固定点使用。

Study of the reproducibility of the superfluid transition temperature of helium

Based upon the dramatic change in thermal conductivity of liquid heliumat at thetemperature of the transition between superfluid (He Ⅱ) and normal fluid (He I), a sealed-cell with a capillary has been used to determine the superfluid transition temperature, T_λ. A controlled small heat flow is passed through the capillary of the sealed cell to realize the coexistence of He I and He Ⅱ and maintain the He Ⅰ/He Ⅱ interface in the capillary. A stable and flat lambda transition temperature plateau is obtained. Because there is a depression of T_λ by the heat flow through the capillary, a series of heat flows and several temperature plateaus are made and an extrapolation is applied to determine T_λ with zero heat flow. A rhodium iron resistance thermometer with series number of A34（RIRT A34）was used in 24 experiments to determine the superfluidtransition temperature with a standard deviation of 0.022mK, which demonstrates the stability and reproducibility of T_λ. We therefore recommend that superfluid transition temperature of helium be used as a fixed point on the International Temperature Scale.