New Avogadro Spheres for the Redefinition of the Kilogram

2014 ◽  
Vol 613 ◽  
pp. 17-25 ◽  
Author(s):  
Arnold Nicolaus ◽  
Rudolf Meeß ◽  
Guido Bartl
Keyword(s):  
Measurement Uncertainty ◽  
International System ◽  
Fundamental Constant ◽  
Machining Process ◽  
Average Roughness ◽  
Weights And Measures ◽  
Avogadro Constant ◽  
System Of Units ◽  
Surface Deviations ◽  
Form Deviation

The General Conference on Weights and Measures (CGPM) discusses the improvements of a possible revision of the International System of Units (SI). For the new definition of the kilogram apart from an artifact of Platinum-Iridium a suitable fundamental constant seems to be found, to which the kg could be related. Although the Planck constant, h, is being considered for the new definition, its value can currently be determined with less uncertainty from the value of the Avogadro constant, NA. As well the determination of the Avogadro constant is suitable as a primary method for the subsequent realization of the kilogram. The international Avogadro group has reached so far a relative measurement uncertainty of 3×10-8, mainly limited by the interferometric measurement of the volume of the 28Si-spheres, used to count the atoms. The dominant influence on the measurement uncertainty is a contribution which subsumes wavefront aberrations due to surface deviations and irregularities of the spheres polished from our partner at CSIRO, Australia. A new multi-step machining process, developed and realized at PTB, reduces considerably the surface contamination and creates spheres with surface properties which exceed the standards in matters of form deviation and surface roughness. The manufacturing process incorporates highly reproducible multi-step grinding and polishing steps. The surfaces are almost free of scratches and show average roughness values below 0.3 nm. The form shows some regular, long wavelength errors below 30 nm in amplitude, collocated conform to crystal orientation.

scholarly journals A new definition for the mole based on the Avogadro constant: a journey from physics to chemistry

2011 ◽  
Vol 369 (1953) ◽  
pp. 3993-4003 ◽  
Author(s):  
Martin J. T. Milton
Keyword(s):  
Measurement Uncertainty ◽  
Early Development ◽  
International System ◽  
Atomic Masses ◽  
Amount Of Substance ◽  
Avogadro Constant ◽  
System Of Units ◽  
Considerable Debate ◽  
Recent Addition ◽  
Base Units

The mole is the most recent addition to the set of base units that form the International System of Units, although its pre-cursor the ‘gram-molecule’, had been in use by both physicists and chemists for more than 120 years. A proposal has been published recently to establish a new definition for the mole based on a fixed value for the Avogadro constant. This would introduce consistent relative uncertainties for the molar and the atomic masses while making no change to the system of relative atomic masses (‘atomic weights’). Although the proposal would have little impact on the measurement uncertainty of practical work, it has stimulated considerable debate about the mole and the nature of the quantity amount of substance. In this paper, the rationale for the new definition is explained against the background of changes in the way the quantity amount of substance has been used, from its first use during the early development of thermodynamics through to the use of the ‘number of gram-molecules’ at the end of the nineteenth century.

Revision of the SI: The Determination of the Avogadro Constant as the Base for the Kilogram

2014 ◽  
Vol 613 ◽  
pp. 3-10 ◽  
Author(s):  
Arnold Nicolaus ◽  
Horst Bettin ◽  
Michael Borys ◽  
Ulrich Kuetgens ◽  
Axel Pramann
Keyword(s):  
International System ◽  
Fundamental Constant ◽  
Lattice Parameter ◽  
Planck Constant ◽  
Avogadro Constant ◽  
System Of Units ◽  
Working Groups ◽  
Fixed Constant ◽  
Watt Balance

At least four units of the International System of Units (SI) are on the way to a new definition. Especially for the unit of mass, the kilogram, a rigorous change is considered. Instead of the current definition, a 1kg-artifact in form of a Pt-Ir-cylinder, the intended formulation relates the unit of mass to a fundamental constant. In detail this requires in a first step a measurement of the chosen fundamental constant with contemporary lowest uncertainty and best reproducibility. The constant will then be fixed to that value. As an example the metre is related to the fixed constant speed of light.For the kg there are considered two ways: one is a watt balance, which determines the mass in units of the Planck constant, h. While at present the watt balances show a heterogeneous appearance, the second class of experiment the determination of the Avogadro constant, NA, which measures the mass in terms of the number of elementary entities has reached a considerable level of uncertainty and reproducibility. The fundament of the new determination of the Avogadro constant is a highly enriched 28Si crystal. The different working groups of the Avogadro team determine molar mass and lattice parameter of the crystal, and mass and volume of two precision spheres made from different positions, but of the same crystal. All measurements are carried out for both spheres and all measurement quantities are determined at least from two independent working groups, usually of different countries.

Dimensions of plane and solid angles and their units in the International System of Units (SI)

2020 ◽  
pp. 26-32
Author(s):  
M. I. Kalinin ◽  
L. K. Isaev ◽  
F. V. Bulygin
Keyword(s):  
Solid Angle ◽  
International System ◽  
International Committee ◽  
Plane Angle ◽  
Arc Length ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
In Series ◽  
Solid Angles

The situation that has developed in the International System of Units (SI) as a result of adopting the recommendation of the International Committee of Weights and Measures (CIPM) in 1980, which proposed to consider plane and solid angles as dimensionless derived quantities, is analyzed. It is shown that the basis for such a solution was a misunderstanding of the mathematical formula relating the arc length of a circle with its radius and corresponding central angle, as well as of the expansions of trigonometric functions in series. From the analysis presented in the article, it follows that a plane angle does not depend on any of the SI quantities and should be assigned to the base quantities, and its unit, the radian, should be added to the base SI units. A solid angle, in this case, turns out to be a derived quantity of a plane angle. Its unit, the steradian, is a coherent derived unit equal to the square radian.

scholarly journals Adapting the International System of Units to the twenty-first century

2011 ◽  
Vol 369 (1953) ◽  
pp. 3907-3924 ◽  
Author(s):  
Ian M. Mills ◽  
Peter J. Mohr ◽  
Terry J. Quinn ◽  
Barry N. Taylor ◽  
Edwin R. Williams
Keyword(s):  
International System ◽  
International Committee ◽  
First Century ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
Magnetic Constant ◽  
Base Units ◽  
New Si

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed.

scholarly journals Definition of the mole (IUPAC Recommendation 2017)

2018 ◽  
Vol 90 (1) ◽  
pp. 175-180 ◽  
Author(s):  
Roberto Marquardt ◽  
Juris Meija ◽  
Zoltán Mester ◽  
Marcy Towns ◽  
Ron Weir ◽  
...  
Keyword(s):  
International System ◽  
International Committee ◽  
Fundamental Physical Constants ◽  
Weights And Measures ◽  
Technical Report ◽  
System Of Units ◽  
Iupac Recommendation ◽  
Definition Of ◽  
Base Units ◽  
Fundamental Physical

AbstractIn 2011 the General Conference on Weights and Measures (CGPM) noted the intention of the International Committee for Weights and Measures (CIPM) to revise the entire International System of Units (SI) by linking all seven base units to seven fundamental physical constants. Of particular interest to chemists, new definitions for the kilogram and the mole have been proposed. A recent IUPAC Technical Report discussed these new definitions in relation to immediate consequences for the chemical community. This IUPAC Recommendation on the preferred definition of the mole follows from this Technical Report. It supports a definition of the mole based on a specified number of elementary entities, in contrast to the present 1971 definition.

scholarly journals Systematic comparison of post-column isotope dilution using LC-CO-IRMS with qNMR for amino acid purity determination

2019 ◽  
Vol 411 (27) ◽  
pp. 7207-7220
Author(s):  
Philip J. H. Dunn ◽  
Dmitry Malinovsky ◽  
Eli Achtar ◽  
Cailean Clarkson ◽  
Heidi Goenaga-Infante
Keyword(s):  
Measurement Uncertainty ◽  
Isotope Dilution ◽  
International System ◽  
Direct Analysis ◽  
Uncertainty Budget ◽  
Chemical Oxidation ◽  
Resonance Spectroscopy ◽  
Purity Determination ◽  
System Of Units

Abstract Determination of the purity of a substance traceable to the International System of Units (SI) is important for the production of reference materials affording traceability in quantitative measurements. Post-column isotope dilution using liquid chromatography-chemical oxidation-isotope ratio mass spectrometry (ID-LC-CO-IRMS) has previously been suggested as a means to determine the purity of organic compounds; however, the lack of an uncertainty budget has prevented assessment of the utility this approach until now. In this work, the previously published ID-LC-CO-IRMS methods have not only been improved by direct gravimetric determination of the mass flow of 13C-labelled spike but also a comprehensive uncertainty budget has been established. This enabled direct comparison of the well-characterised ID-LC-CO-IRMS method to quantitative nuclear magnetic resonance spectroscopy (qNMR) for purity determination using valine as the model compound. The ID-LC-CO-IRMS and qNMR methods provided results that were in agreement within the associated measurement uncertainty for the purity of a sample of valine of (97.1 ± 4.7)% and (99.64 ± 0.20)%, respectively (expanded uncertainties, k = 2). The magnitude of the measurement uncertainty for ID-LC-CO-IRMS determination of valine purity precludes the use of this method for determination of purity by direct analysis of the main component in the majority of situations; however, a mass balance approach is expected to result in significantly improved measurement uncertainty.

scholarly journals World Metrology Day, 20 May 2018

2018 ◽  
Vol 40 (2) ◽  
pp. 31-31
Keyword(s):  
International System ◽  
Science And Technology ◽  
Measurement Methods ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Measurement Science ◽  
To Come ◽  
Quantum Phenomena

Abstract The theme for World Metrology Day 2018 is Constant evolution of the International System of Units. This theme was chosen because in November 2018, the General Conference on Weights and Measures is expected to agree one of the largest changes to the International System of Units (the SI) since its inception. The proposed changes are based on the results of research into new measurement methods that have used quantum phenomena as the basis for standards that are fundamental.  The SI will be based on a set of definitions each linked to the laws of physics and have the advantage of being able to embrace further improvements in measurement science and technology to meet the needs of future users for many years to come.

Bye-Bye, IPK!

2019 ◽  
Vol 41 (2) ◽  
pp. 53-54
Author(s):  
Daniel Rabinovich
Keyword(s):  
Electric Current ◽  
International System ◽  
Golf Ball ◽  
Weights And Measures ◽  
Units Of Measurement ◽  
International System Of Units ◽  
System Of Units ◽  
Utmost Care ◽  
Physical Quantities

Abstract The International Prototype Kilogram, after 130 years of dutiful service, is finally retiring. The IPK, a golf ball-sized cylinder made of a special platinum-iridium alloy (90:10), was introduced in 1889 at the first General Conference on Weights and Measures (CGPM) near Paris to define the unit of mass using an artifact fabricated with the utmost care and precision available at the time. New units were subsequently adopted for other physical quantities such as electric current (the ampere) and temperature (the kelvin), and the increasing need for a more cohesive set of units of measurement led to the implementation of the International System of Units (SI) in 1960.

TOWARD THE REDEFINITION OF THE KILOGRAM FROM THE 28Si INTERNATIONAL RESEARCH PROJECT

2013 ◽  
Vol 24 ◽  
pp. 1360001
Author(s):  
KENICHI FUJII
Keyword(s):  
International Research ◽  
International System ◽  
Physical Constant ◽  
Standard Uncertainty ◽  
Research Project ◽  
Avogadro Constant ◽  
Counting Procedure ◽  
System Of Units ◽  
Fundamental Physical ◽  
International Research Project

In the international system of units, the kilogram in the only SI base unit still defined by a material artefact. In order to redefine this unit with a fundamental physical constant, an international research project was launched in 2004 for determining the Avogadro constant, NA, by counting the atoms in an isotopically enriched 28Si crystal. The counting procedure relies on the measurements of the molar and atomic volumes of 1 kg spheres made of the 28Si crystal. In 2011, the project succeeded in measuring the Avogadro constant with a smallest standard uncertainty, 3.0 × 10−8 NA. Because of an unexpected metallic contamination at the surface of the spheres, the measurement uncertainty was larger than the target of the project by a factor of 1.5. In order to further reduce the uncertainty, a new international research project was launched in 2012. Outline of the new project and the improvements of the measurements will be introduced at the forum. Note from Publisher: This article contains the abstract only.

scholarly journals The Proposed New SI: Consequences For Mass Metrology

ACTA IMEKO ◽  
2014 ◽  
Vol 3 (2) ◽  
pp. 3 ◽  
Author(s):  
Roman Schwartz ◽  
Michael Borys
Keyword(s):  
International System ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Future Revision ◽  
New Si

At its 24<sup>th</sup> meeting in October 2011 the General Conference on Weights and Measures (CGPM) adopted a Resolution on the possible future revision of the International System of Units (SI). This paper provides an overview of the proposed changes to the SI, the focus being on the proposed redefinition of the kilogram and possible consequences for mass metrology.<br />

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