Further results on the triple point temperature of pure 20Ne and 22Ne

The paper reports further results following the 2010 determinations at INRIM of the triple point temperature of the neon isotopes 20Ne and 22Ne, obtained on nearly-pure samples sealed in cryogenic cells, carrying an uncertainty much lower than the previous determinations. The further results, performed in the same experimental apparatus with an expanded uncertainty (k 2) of 30 lK for a single cell and 50 lK for the comparison of sample pairs, were obtained using the same model of cryogenic metal sealed cell for each sample, and by measuring different samples from the same gas batch of each isotope and from different gas batches showing a different content of isotopic and chemical impurities. The new determinations were intended to check the effect of measuring different samples and the gas batches, and of performing corrections based on different analytical assays for the isotopic and chemical impurities. The new results are in agreement with the previous determinations, confirming, with greater confidence, the value of the temperature difference for the two pure isotopes, 0.14658 K with an expanded uncertainty of 0.00007 K, and the temperature values on ITS-90 24.5422 K for 20Ne and 24.6888 K for 22Ne, within the larger expanded uncertainty, 0.00032 K, due to the present ambiguity of the ITS-90 definition. These values are also consistent with new determinations published by other laboratories. In addition, the ITS-90 values of INRIM 2010 determinations of Ttp of samples of neon (INRIM Ec2Ne, INRIM E4Ne, PTB Ne12, NPL Ne2) of natural isotopic composition with different 22Ne amount concentrations are reported, consistent with the values obtained for pure isotopes.