Anomalous behavior of a tin point cell

At NMIJ, AIST, ensembles of fixed point cells are maintained for each defining fixed point to underpin the confidence for the maintenance of the national standards for thermometry. As a routine work, fixed point cells for the same temperature are realized simultaneously and the temperature differences between them are measured when the liquid fraction (1/F) is between 1 and 2. An anomalous temperature difference of approximately 0.2 mK was observed for one tin point cell. In this paper, we report the details of this anomalous temperature difference, and also the analysis to elucidate its cause. We assume that such anomalous behavior probably occurred due to condensation of impurities by employing a specific realization method repeatedly. Also we present that the anomalous behavior appears to be resolved by adopting another realization method during the experiments conducted under the present work.