Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of $N_A = 6.022 140 76(12) \times 10^{23}$ mol$^{-1}$. The X-ray crystal density method has thus achieved the target relative standard uncertainty of $2.0 \times 10^{-8}$ necessary for the realization of the definition of the new kilogram.Comment: postprint, 22 page, 3 figures, 14 table

Quantum SI: The New System of Units

This article gives an overview of the new SI and a few details as to how its setting up was achieved. Those interested in the story of how the kilogram was fixed by tying it to the Planck constant can go straight to section five. Otherwise, apart from the introduction given as section one which also presents excerpts from the relevant official documents on key aspects of the new system, section two gives a brief timeline of the history of the decimal metric system, section three gives a few details of the procedural steps -- from the setting up of a standard of measurement to its percolation to the public, taking the time standard as an example and, section four attempts to give a flavour of the actual process of the setting up of a standard.Comment: 16 pages, 5 figures, written for Resonance - Journal of Science Education, published by the Indian Academy of Science

A new generation of 99.999% enriched 28Si single crystals for the determination of Avogadro's constant

A metrological challenge is currently underway to replace the present definition of the kilogram. One prerequisite for this is that the Avogadro constant, NA, which defines the number of atoms in a mole, needs to be determined with a relative uncertainty of better than 2  ×  10−8. The method applied in this case is based on the x-ray crystal density experiment using silicon crystals. The first attempt, in which silicon of natural isotopic composition was used, failed. The solution chosen subsequently was the usage of silicon highly enriched in 28Si from Russia. First, this paper reviews previous efforts from the very first beginnings to an international collaboration with the goal of producing a 28Si single crystal with a mass of 5 kg, an enrichment greater than 0.9999 and of sufficient chemical purity. Then the paper describes the activities of a follow-up project, conducted by PTB, to produce a new generation of highly enriched silicon in order to demonstrate the quasi-industrial and reliable production of more than 12 kg of the 28Si material with enrichments of five nines. The intention of this project is also to show the availability of 28Si single crystals as a guarantee for the future realisation of the redefined kilogram

Reforming the international system of units: On our way to redefine the base units solely from fundamental constants and beyond

Our purpose is to offer a logical analysis of the system of units and to explore possible paths towards a consistent and unified system with an original perspective. The path taken here builds on the fact that, thanks to optical or matter-wave interferometry, any measurement can be reduced to a dimensionless phase measurement and we follow this simple guiding line. We finally show how one could progress even further on the path of a synthetic framework for fundamental metrology based upon pure geometry in five dimensions

Dissemination of the « Planck-Kilogram »

Metrologists all over the world are looking at the activities of the Metre Convention concerning the New International System of Units on the basis of fundamental constants. Especially the redefinition of the kilogram will have consequences in nearly all fields of physics, engineering and trade. A new definition of a base unit imperatively implies thoughts about the future dissemination of the unit. After a short glance at the potential of the Kibble(Watt)-Balance the presentation will describe the strategy of the Physikalisch-Technische Bundesanstalt to use silicon spheres of different qualities for the dissemination of the quantum based kilogram to the macroscopic world. Beside metrological aims the availability of realisations is of crucial importance within a future dissemination chain. Aspects like the connection to the established system as an important aspect for acceptance, the applicability of the developed tools and procedures for using such spheres as mass standards or the current state of activities to proof the expected excellent long term characteristics of silicon spheres in use will be presented

A new 28Si single crystal: counting the atoms for the new kilogram definition

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