The triple point of water serves to define the kelvin, the unit of thermodynamic temperature, in the International System of Units (SI). Furthermore, it is the most important fixed point of the International Temperature Scale of 1990 (ITS-90). Any uncertainty in the realization of the triple point of water contributes directly to the measurement uncertainty over the wide temperature range from 13.8033 K to 1234.93 K.The Consultative Committee for Thermometry (CCT) decided at its 21st meeting in 2001 to carry out a comparison of water triple point cells and charged the BIPM with its organization.Water triple point cells from 20 national metrology institutes were carried to the BIPM and were compared with highest accuracy with two reference cells. The small day-to-day changes of the reference cells were determined by a least-squares technique. Prior to the measurements at the BIPM, the transfer cells were compared with the corresponding national references and therefore also allow comparison of the national references of the water triple point.This report presents the results of this comparison and gives detailed information about the measurements made at the BIPM and in the participating laboratories. It was found that the transfer cells show a standard deviation of 50 µK; the difference between the extremes is 160 µK. The same spread is observed between the national references.The most important result of this work is that a correlation between the isotopic composition of the cell water and the triple point temperature was observed. To reduce the spread between different realizations, it is therefore proposed that the definition of the kelvin should refer to water of a specified isotopic composition.The CCT recommended to the International Committee of Weights and Measures (CIPM) to clarify the definition of the kelvin in the SI brochure by explicitly referring to water with the isotopic composition of Vienna Standard Mean Ocean Water (VSMOW). The CIPM accepted this recommendation and the next edition of the SI brochure will include this specification.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

This is a summary of the Consultative Committee for Thermometry (CCT) Key Comparison CCT-K3, i.e. the comparison of realizations of the fixed points of the International Temperature Scale of 1990 (ITS-90) over the range 83.8058 K to 933.473 K. The differences in the realizations of the various fixed points in this range of the ITS-90 and the uncertainties of those differences are given for the fifteen standards laboratories participating in the comparison.

The anisotropic emission of the K-X-radiation of boron and nit'rogen in hexagonal boron nitride BN permits the determination of the x -and a-subbands of the two X-ray spectra. Together with the X-ray photoelectron spectrum a consistent picture of the valence band of BN is obtained. Position and width of the s-, o-, and x-bands are determined. None of the band structure and density-of-states calculations known so far is in satisfactory agreement with the experimental observations. Die anisotrope Emission der K-Rontgenstrahlung von Bor und Stickstoff in hexagonalem Bornitrid BPU' erlaubt die Bestimmung der x -und a-Teilbanden der beiden Ront,genspektren. Zusammen mit dem Rontgen-Photoelektronenspektrum ergibt sich daraus ein konsistentes Bild des Valenzbandes von BN. Breite und Lage der s-, a-und x-Bande werden bestimmt. Keine der vorliegenden Bandstruktur-und Zustandsdichteberechnungen zeigt eine zufriedenstellende Ubereinstimmung mit den experimenbellen Beobachtnngen.

A self-calibration procedure is presented for semiconductor photodiodes to be used as detectors in the soft x-ray region. In this procedure the spectral responsivity is calculated according to a model from experimentally accessible parameters of the detector. The thicknesses of the dead layer and the space charge region as well as the diffusion length have been determined in monochromatic radiation by investigating the angular dependence of the photocurrent. The mean energy for electron-hole pair creation has been determined in calculable undispersed synchrotron radiation of the primary standard source BESSY. The obtained uncertainties of the spectral responsivity in the photon energy region between 150 and 2500 eV are ≤4.2% for newly developed Si n on p diodes and ≤6% for GaAsP/Au diodes. The calibrated photodiodes were used to determine the quantum efficiency of photoemissive gold diodes which is up to four orders of magnitude lower than that of semiconductor photodiodes.

The quantum efficiencies of semiconductor photodiodes have been measured at photon energies from 5 to 3500 eV. For silicon photodiodes strong radiation-induced effects were found. GaAsP and GaP Schottky diodes show remarkable stability and high quantum efficiency. Use of Schottky diodes for spectroscopic and radiometric measurements is discussed.