RECENT MEASUREMENTS OF EUROPEAN DEUTERIUM CELLS AT NPL

摘要

The last five years of work at NPL on the (ongoing) evaluation of the deuterium triple point (～18.7 K) as a candidate for a replacement fixed point of the International Temperature Scale, is described. The "EUROMET 1" D_2 cell has been further measured (now spanning ten years) and the apparent drop in the triple point value due to internal contamination is 0.4 mK. Further results from a cell using a copper pinch-seal and an all-copper D2 cell are reported. A new "VAR" stainless steel cell produced and filled from an IMGC store of gas, originating from the same supplier of gas as used in the EUROMET 1 cell, has returned a result of 18.6878 K, which is 1.4 mK below the original EUROMET 1 value of 10 years ago. The thermal characteristics of this cell have been compared with the EUROMET 1 cell. Although some chromium compounds have been tried, no alternative to Gd_2O_3 as a non-contaminating para-ortho catalyst has been found. Suggestions for the future course of the work are outlined