C2. Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO)

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Report to the 1999 General Assembly for 1996-99

1. Introduction

The Commission encourages and promotes the exchange of information and views of the members of the international community in the general field of physical measurements, pure and applied metrology, nomenclature and symbols for physical quantities and units. It encourages work contributing towards improved values of atomic masses and fundamental physical constants and facilitating their universal adoption.

These objectives have been pursued in a number of ways in the past. These have included encouraging and sponsoring appropriate conferences, by the award of the SUNAMCO Medal for outstanding work by scientists in this area, by the publication of a booklet for physicists on the Symbols, units and nomenclature and fundamental constants in physics (IUPAP-25), and by participation with other international organisations in the production of recommendations by related international committee activities. These and other activities have continued during the last two years as is reported below

2. Meetings

In order to minimise time and costs, wherever possible Commission meetings are arranged to be held during an international conferences which most of the Commission members are attending. A majority of members of the Commission attended a meeting that took place at the CPEM98 conference in July 1998. A further (essentially complementary) meeting comprising those members concerned with atomic masses took place at the ENAM98 Conference. One important topic was the production of the next issue of the IUPAP booklet IUPAP:25, Symbols, Units, Nomenclature and Fundamental Constants. The Vancouver meeting of the IUPAP Executive in October confirmed that the booklet was considered useful by physicists and that a further edition would be welcomed by physicists. It is hoped to make it available on the WWWeb and the prospective publisher has agreed to this.

3. SUNAMCO Medal

The SUNAMCO Medal is awarded to organisations as well as to individuals for outstanding work in the area of physics covered by the terms of reference of the Commission. The Chairman has obtained a further supply of Medals. Two medals have been awarded during the period reported on. The citations are given in the appendix to this report. The citations for these and the earlier SUNAMCO medal winners are given as part of the IUPAP:C2 WWWeb site entry.

The sixth in the series of SUNAMCO Medals was awarded by the Commission to Professor T Kinoshita for his work on Quantum Electro-Dynamic calculations of the electron magnetic moment anomaly in terms of the fine structure constant, and its key role in enabling the precision measurements of this quantity at the University of Washington to be applied to evaluating both the value of the fine structure constant and the SI unit of resistance. The medal was presented to Professor Kinoshita by Professor Emilio Zavattini at a ceremony during the Banquet at the 'Workshop on Frontier Tests of QED': Sandansky, Bulgaria. 9th -15th July 1998. The citation was read by Dr Peter Mohr.

The seventh in the series of SUNAMCO medals was awarded by the Commision to Gemainschaft fuer Schwer-Ion Forschung GSI (The laboratory for research with heavy ions) in Darmstadt (GSI, Darmstardt) for their precision measurements of the atomic masses of heavy nuclei., including both their contribution to the determination of masses both in the region of mass numbers 140-200 and to that of new, very heavy elements. The medal was presented to Dr Hans Geissel and Dr Sigurd Hofmann , who received it on behalf of the GSI,at a ceremony during the Second International Conference on Exotic Nuclei and Atomic Masses (ENAM98), Belaire, Michigan USA. The medal was presented to GSI by Dr. A. H. Wapstra

4. Conferences

The scientific coverage of the bi-annual series of CPEM conference falls specifically in the field of physics of interest to the Commission, and they have been sponsored regularly by the Commission. The same is true for a series of conferences on atomic masses, earlier known as the SUN-AMCO conferences. Since the theoretically most relevant part of the work is concerned with masses far from stability this series has fused with a regular tri-annual series of conferences in the latter field to become the conferences on Exotic Nuclei and Atomic Masses (ENAM).

The three sponsored conference were:

  1. The Conference on Precision Electromagnetic Measurements (CPEM-96) June 1996 in Braunschweig, Germany
  2. The Conference on Precision Electromagnetic Measurements (CPEM-98) July 1998 in Washington DC, USA
  3. The Conference on Exotic Nuclei and Atomic Masses (ENAM-98) June 1998 in Bell Aire, Michican, USA

5. Activities

5.1 Nomenclature
Unambiguous communication is required between physics and other sciences and technologies. This is essential if we are to rely on the work of others and make use of it in our own endeavours. The international measurement system must necessarily be able to respond to changes that are required to match advances in science and technology. These changes affect the SI system of quantities, the SI system of units (including how well they are known and transferred to the laboratory concerned), the vocabulary of measurement, and the method of conveying to others how well the measurement has been made.

An important part of the activities of the Commisison lies in representing the interests of physicists on symbols, units, nomenclature, etc, to other international organisations. This is particularly important in order for the Commission to serve the interests of those Applied Physicists from all parts of Physics whose work is subject to the decisions of such organisations. This aspect of the work of the Commission has been of particular concern and emphasis during the last IUPAP cycle. Every endeavour is made to achieve an acceptable compromise between what physicists ideally want and what is wanted by scientists and technologists from other scientific disciplines. It is accepted that physicists will always be likely to require a local system of units in order to consider a particular problem. Thus, constancy of the speed of light is implicit in the SI definition of the unit of length, and physicists may wish to investigate this constancy theoretically and experimentally. However, it is helpful to other scientists and technologists who are outside the particular specialisation if the value of such units is given in terms of SI units the first time that they are used.

In the field of nomenclature, the Commission participated in the preparation of the first editions of the GUM (Guide to the Expression of Uncertainty in Measurement; English version 1993, French version 1995) and the VIM (Vocabulaire International des Termes Fondamentaux et Généraux de la Métrologie; bilingual). These were prepared on behalf of BIPM, IEC, IFCC, ISO, OILM, IUPAC and IUPAP. The aim of IUPAP participation is, that physicists moving to different jobs in different scientific areas during their career are subject to similar practices. The chairman of C2 has been involved in setting up an International Committee for the production of Joint Guides on Basic Metrology, to be known as JCGM. In the longer term this organisation will attack metrological problems of a broadly similar nature to the GUM and VIM that have long awaited an agreed solution. The aim is to issue guides which will be endorsed by the organisations concerned and incorporated as a basis for their own recommendations. The GUM and VIM have been widely welcomed and are in process of being revised by the JCGM.

The Commission Chairman also has attended meetings of the Consultative Committee on Units on behalf of IUPAP. This Committee has been in process of producing a revised edition of the brochure on SI units and this was submitted to the CIPM for approval. This has now been published (Le Système International d'unitès, 7th Edition, BIPM, France) Following representations from IUPAP which were supported by IUPAC, this edition incorporates the radian and steradian as dimension-less derived units. The neper and bel are now dimension-less units used alongside the SI. There is a slightly more user friendly approach to the use of non-SI units alongside the SI, particularly the CGS units which are still used widely by many physicists. There is a strong drive from outside IUPAP to introduce further dimension-less units into the class of SI derived units, including the introduction of a name and symbol for the dimension-less quantity unity. This could allow SI prefixes to be associated with dimension-less quantities.

The SI Brochure also incorporates the IUPAP suggested the revision of the definition of the atomic mass unit, and the consequential revision to the note accompanying the definition of the mole.

Further revisions lie in the future, such as putting the definitions of the SI base units into a common format, and revising them to reflect the increased accuracy required by modern science and technology.

The Commission has also prepared the SUNAMCO Web site.

5.2. Atomic Masses

In the field of atomic masses, a new complete table was published in December 1993 (397 pages). In response to requests from users, Audi and Wapstra plan to publish updates every 2 years. These updates essentially give only a table of mass excesses and the new experimental data used (the first such review came out late in 1995 (72 pages); and the next complete table is due in 1999.

There is a noticeable influence on the accuracy of the evaluation resulting from derivation of mass values from measurement of cyclotron frequencies in ion traps, leading, for example, to an order of magnitude improvement for the most important stable nuclides. Measurements in ion storage rings will lead to notable improvements, but may cause a certain delay in the issue of the mass table. There have also been many measurements of proton and alpha decay energies which have greatly improve the knowledge of atomic masses of nuclides close to the proton drip line.

An overview of the present situation was presented in a report to ENAM98 by A. H. Wapstra and G. Audi, and this overview will be published in its proceedings.

5.3. The Naming and Discovery of the Trans-fermium elements.

The Chemistry Union has decided to recommend the use of the names given in the following table for the elements 101 to 109, following the advice of the IUPAC Commission on the Nomenclature of Inorganic Chemistry


It is hoped that these names will find universal acceptance in the scientific and technological community.

A joint IUPAP/IUPAC Committee has now been set up to consider the discovery of elements 110-112. The Chairmen of IUPAP Commissions C2 and C12 have agreed to participate in this.

5.4. Fundamental Constants:

The CODATA (evaluation of the 'best values' of the Fundamental constants has been delayed for several reasons (including recent rapid advances in the accuracy of measurements in this area)and a new evaluation is expected to be available in 1999. The strong influence of a comparatively a small number of measurements on the recommended values, and the desirability of stronger supportive evidence has been an important consideration.

An interim report was given at CPEM96, at which conference a certain amount of relevant new work was reported. Aside from the universal gravitational constant, the experimental evidence to date favours a more accurate set of values. After taking into account the 1987 assigned uncertainties the new values are not expected to be significantly different from the 1987 values. New measurements include a re-measurement of the wavelength of the gamma-rays emitted in the mass of the neutron, slightly beyond the earlier estimated error; improved estimates of the fine structure constant from laser spectroscopy on cold caesium atoms; further measurements of the watt play a pivotal part. More accurate realisations of the watt have been made by the moving coil method and these critically affect the accuracy of the measurements of many fundamental constants, including the electron and proton rest masses, the elementary charge, and the Planck constant. The Rydberg constant is now measured with sufficient accuracy to be part of the mise en pratique for the metre.

6. Appendix: Citations for the awards of the sixth and seventh SUNAMCO Medals

6.1. Citation for the award of the sixth SUNAMCO Medal: to Professor Tochiro Kinoshita - 1998.

Professor Toichiro Kinoshita is awarded a SUNAMCO Medal by IUPAP: Commission C2, the SUNAMCO Commission, by virtue of the contributions that his work has made to the part of physics within its terms of reference. In particular it is awarded for the aspects of his work relating to the evaluation of the 'best values' of the fundamental physical constants. This latter topic forms one of the main interests of the work SUNAMCO Commission.

The work of Professor Kinoshita is very apposite to the work of the Commission. It both exemplifies the enduring interaction between pure and applied physics, and also provides a particularly good example of the increasingly strong links between theoretical physics and modern science and technology.

His calculations of the anomalous magnetic moment of the electron and of the muon, and of the muonium ground-state hyperfine splitting, presently provide a major bridge between the measurements of these physical quantities and the evaluation of the best values of the fine-structure constant, the muon- electron mass ratio, and the muon-proton magnetic moment ratio.

His calculations of the eighth-order coefficient in the theoretical expression of the anomalous magnetic moment of the electron, and similar coefficients in the expression for the anomalous magnetic moment of the muon, are something of a tour de force, involving as they do the evaluation of hundreds of complex Feynman diagrams, together with other quantum electro-dynamic (QED) and non-QED contributions, including hadronic corrections.

Professor Kinoshita's work has permitted the evaluation of the fine-structure constant from experimental determinations of the electron anomaly with a relative uncertainty of less than 10-8. The comparison of the values derived for the fine-structure constant from different types of measurement provides a critical check on the correctness of our understanding of different parts of physics.

An important feature of his calculations has been the careful attention paid to the evaluation of the uncertainties associated with his calculations. He has provided estimates of the uncertainties of the terms that he has calculated, and also made estimates of the uncertainties of contributions from the un-calculated higher-order terms. His work provides an example to all theoretical physicists of how their treatment of the uncertainties of their calculations should mirror the methods commonly encountered in experimental measurements. The proper treatment of uncertainties is difficult, but is a task that IUPAP Commission C2 would like to encourage all physicists to pursue.

His painstaking approach, and the attention to detail involved in the calculations, also mirrors the problems encountered with the accurate measurements of physical quantities. He has therefore, by the inherent nature of his theoretical work, had much in common with the experimental meteorologists whose work is also covered by the SUNAMCO Commission. The Commission therefore takes great pleasure in awarding a SUNAMCO Medal to Toichiro Kinoshita.

6.1.1. Presentation

The medal was presented to Professor Kinoshita by Professor Emilio Zavattini at a ceremony during the Banquet at the 'Workshop on Frontier Tests of QED': Sandansky, Bulgaria. 9th -15th July 1998. The citation was read by Dr Peter Mohr.

6.2. Citation for the award of the seventh SUNAMCO Medal to GSI, Darmstadt.

The SUNAMCO medal is awarded by IUPAP Commission C2, to persons or Institutions, who have made outstanding contributions in one of its fields of interest. In 1998 one of these medals was awarded to the GSI, the "Gemeinschaft fur Schwer-Ionforschung" (Company for research with heavy ions) in Darmstadt, Germany

The knowledge of the atomic masses with the highest possible accuracy has been a subject of major interest for the SUNAMCO Commission and its predecessors for several tens of years. Currently the masses of stable isotopes are known with rather satisfactory accuracy. The main interest in the field has therefore shifted to the masses of rather unstable nuclides ("exotic" nuclides.) Two groups of these can be distinguished. One of them is those nuclides which are far removed of the line of beta-stability in a plot of number of neutrons versus number of protons. The other group concerns very heavy nuclides, such as those with nuclear charge numbers beyond 100 (the transfermium elements.)

Direct mass measurements in the first field were pioneered by a French group working at Isolde in CERN, Geneva, using a classical mass spectrometer. At the same place, a group led by scientists from Mainz (Germany) has reached higher accuracy using Penning traps. Further mention should also be made of the time-of-flight measurements made in Los Alamos, USA and in Caen, France. Similarly, important work in the second field has also been done by laboratories in Berkeley (California) and Dubna (Russia).

However, outstanding contributions in both fields have been made by the GSI. Work in this Institute has permitted the investigation of the properties of the ions of exotic nuclides which are produced in collisions of heavy ions with suitable, thin targets.

For precision mass measurements, the product ions are subsequently selected by a "Projectile Fragment Separator" and are collected in a storage ring. These are then "cooled" by interaction with an electron beam, producing a limited spread in their velocities. They then travel on different paths, with different circulating frequencies depending on their charge to mass ratio, in the storage ring. By analysing these frequencies, the masses of many dozens of quite exotic nuclear species, in the region of atomic numbers A=156-203, have been determined by the GSI, with precisions of the order of 100 keV.

For investigating ions of transfermium elements, the product ions are first selected in a velocity filter (SHIP) and then pass through a time-of-flight arrangement. It is ascertained that selected ions are evaporation residues, that is, compound nuclei from which only few nucleons are evaporated. These ions are then embedded in position sensitive detectors, which permit the observation of coincidences in place and time between the signals corresponding to embedding the ion and those arising from the alpha-particles of subsequent alpha-decays. Observation, among the latter, of delay- times and (especially) alpha-particle energies which are consistent with those of known nuclides, then allows one to obtain dependable assignments of both the mass and nuclear charge numbers of the embedded particle - even in cases where only one relevant ion was observed. Several new elements have been discovered this way, most recently element 112. The observed alpha-particle energies also allow the derivation of accurate values for the masses of the members of the observed decay chains.

5.2.1. Presentation

The medal was presented to the GSI by Professor Aaldert Wasptra (middle), Secretary of the Commission, at a ceremony during the Second International Conference on Exotic Nuclei and Atomic Masses (ENAM98), Belaire, Michigan USA. Dr Hans Geissel (left) and Dr Sigurd Hofmann (right), received it on behalf of the GSI

B.W. Petley, Chairman
A.H. Wapstra, Secretary

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