Redefinition of the kilogram: a decision whose time has come

Mills, Ian; Mohr, Peter J.; Quinn, Terry; Taylor, Barry N.; Williams, Edwin R.

doi:10.1088/0026-1394/42/2/001

Cited by 194 publications

(180 citation statements)

References 22 publications

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“…The changes to the SI proposed here were suggested by Mills et al [4,5], and were developed by the CCU at its meetings in 2009 and 2010. (The idea of defining the entire SI by a single scaling statement was first put forward in the latter paper [5] and is due to P. J.…”

Section: Definitions and Changes In The Definitions Of The Base Unitsmentioning

confidence: 98%

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

Mills

Mohr

Quinn

et al. 2011

Phil. Trans. R. Soc. A.

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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.

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Section: Definitions and Changes In The Definitions Of The Base Unitsmentioning

confidence: 98%

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

Mills

Mohr

Quinn

et al. 2011

Phil. Trans. R. Soc. A.

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“…The proposal made in 1995 [26] and subsequently clarified in 2009 [27] was for a definition of the mole based on a fixed number of entities. This is expressed in the form: 'The mole is the unit of amount of substance of a specified elementary entity, which may be an atom, molecule, ion, electron, any other particle or a specified group of such particles; its magnitude is set by fixing the numerical value of the Avogadro constant to be equal to exactly 6.02214 × 10 23 when it is expressed in the unit mol −1 .'…”

Section: A Definition Of the Mole Based On A Fixed Number Of Entitiesmentioning

confidence: 99%

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

Milton

2011

Phil. Trans. R. Soc. A.

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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.

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“…The precision with which this isotopic composition can be achieved currently limits the reproducibility of the kelvin realization at a few 10 −7 . A revision of the SI is thus expected in the near future [23][24][25][26][27]. One objective is to avoid using artifacts or macroscopic properties of matter.…”

Section: Introductionmentioning

confidence: 99%

Accurate determination of the Boltzmann constant by Doppler spectroscopy: Towards a new definition of the kelvin

Darquié

Mejri

Sow

et al. 2013

EPJ Web of Conferences

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Abstract. Accurate molecular spectroscopy in the mid-infrared region allows precision measurements of fundamental constants. For instance, measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 m enables a determination of the Boltzmann constant k B . We report on our latest measurements. By fitting this lineshape to several models which include Dicke narrowing or speeddependent collisional effects, we find that a determination of k B with an uncertainty of a few ppm is reachable. This is comparable to the best current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of k B determined by the CODATA. Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing k B , an exciting prospect considering the upcoming redefinition of the International System of Units.

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Redefinition of the kilogram: a decision whose time has come

Cited by 194 publications

References 22 publications

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

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

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

Accurate determination of the Boltzmann constant by Doppler spectroscopy: Towards a new definition of the kelvin

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