About the Influence of Chemical Impurities on the Gallium Temperature Fixed Point

The effects linked with chemical impurities lead generally to the preponderant component in uncertainty budgets of temperature fixed points. It is often very difficult to, reliably, estimate the values of this component. In order to bring complementary information, BNM-INM (France) and LPM-FSB, University of Zagreb (Croatia) have been starting scientific cooperation on this topic. In this frame the temperatures of te solid-liquid transition of 3 different samples of Gallium containing different amounts of impurities have been studied. The SPRT resistance measurements are analysed versus the inverse of the fraction of time passed since the beginning of the transition. The experimental results show that in the case of this study a reasonable estimation of the uncertainty component linked with the impurities effect can be obtained with the help of quadratic function fitting the data corresponding to 30% to 80% percent of the total duration of the plateau.