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Technical Activities 1985 Center for Basic Standards

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Technical Activities 1985 Center for Basic Standards echnical Activities 1985 Center for Basic Standards October 1985 U.S. DEPARTMENT OF COMMERCE National Bureau of Standards * : \ ^ , •. J national bureau OF STANDARDS library NBSIR 85-3254 I / V Center for Basic Standards Karl G. Kessler, Director U.S. DEPARTMENT OF COMMERCE National Bureau of Standards National Measurement Laboratory Center for Basic Standards Gaithersburg, MD 20899 October 1985 U.S. DEPARTMENT OF COMMERCE Malcolm Baldnge, Secretary National Bureau of Standards, Ernest Ambler. Director ABSTRACT This report summarizes the research and technical activities of the Center for Basic Standards during the Fiscal Year 1985- These activities include work in the areas of electricity, temperature and pressure, mass and length, time and frequency, quantum metrology, and quantum physics. Keywords: Astrophysics; atomic and molecular physics; chemical physics; electrical standards; fundamental constants; gravity measurements; laser physics; length standards; mass standards; pressure and vacuum standards; temperature standards; time and frequency standards; X-ray and gamma-ray wavelength standards. i INTRODUCTION This report is a summary of the technical activities of the NBS Center for Basic Standards (CBS) for the period October 1, 1984 to September 30, 1985. The Center is one of the four centers and operating units in the National Measurement Laboratory. The summary of activities is organized in six sections, one for the technical activities of the Quantum Metrology Group, and one each for the five divisions of the Center. Each division or group tells its own story in its own way. In general, there is an overview followed by a series of short reports on current projects. Then the publications, invited, talks, committee participation and professional interactions during the year are listed. More information about particular work may be desired. To obtain this, the reader should address the individual scientists or their division, c/o Center for Basic Standards, B160 Physics Building, National Bureau of Standards, Gaithersburg, Maryland 20899. TABLE OF CONTENTS Abstract i Introduction ii Quantum Metrology Group 1 Electricity Division 21 Temperature and Pressure Division 76 Length and Mass Division 128 Time and Frequency Division 138 Quantum Physics Division 193 iii . QUANTUM METROLOGY GROUP SUMMARY OF ACTIVITIES FISCAL YEAR 1985 OVERVIEW We are engaged in certain relatively clearly defined scientific enterprises and at the same time concerned with development and im-’ provement of tools and measurement technology for future scientific work. This combination of efforts is not so unusual, and for the moment at least, appears advantageous. Indeed much of our current scientific program benefits from earlier technical development exercises and there are indications that this progression may continue in the future. Evidently we benefit from an absence of externally mandated programs and goals which makes planning and program articulation both more difficult and more important. In the following sub-’sections we have attempted to convey our sense of where the work now stands and where at least some of its future may lie. For purposes of internal management and in terms of the external groups and facilities with which we interact, we tend to see two major scientific thrusts: One of these concerns itself with precision measurement, especially of the spectroscopic variety predominantly in the x-ray and Y-ray regions, determination of fundamental constants and tests of basic symmetries and invariances. The second concerns itself with structure and dynamics in atoms, molecules and simple solids perturbed by the presence of one or more inner-shell vacancies. This work ultimately requires radiation fluxes only available at synchrotron radiation sources to separately characterize single vacancy and multiple vacancy processes. However, the ultimate aim is systematic investigation of smaller molecules and other simple systems to establish a stable basis for investigation of less well understood systems. Lastly in this report we indicate current efforts at new technology for scientific measurements. Although it is not easy to impose on these exercises a meaningful programmatic overlay, there are certain features which indicate an appropriateness to our presence in these areas. These indicators include: rather challenging technical obstacles, scientifically attractive potentiality, good local talent and either modesty of scale or effective external collaborative relationships TECHNICAL ACTIVITIES Precision measurements & fundamental constants Objectives and programs : Ongoing work in this area is primarily on spectroscopic measure- ments in the region of x-rays and Y-rays but includes also work on the gravitational constant. Our spectroscopic efforts are focussed at the 1 present time on tests of QED in high Z one- and two-electron systems, systematics of inner vacancy spectra and measurement of those Y-tran- sitions which are directly connectable to fundamental constants and masses of elementary particles. The overall scheme begins with optical interferometry of a crystal (Si) lattice spacing, dissemination of this result to other diffract- ing crystals and their use via absolute angle measurement for wavelength determination. Some of these wavelength determinations are of direct importance in and of themselves, as is the case for the n-p capture Y, while others provide markers for experiments where only relative measurements are feasible, e.g., those involving mesic atoms or one- and two- electron high Z systems. All aspects of this work are currently active and in aggregate involve significant numbers of NBS staff and visitors, as well as considerable resources both internal to NBS and at major international centers. NBS personnel working in this area include R.D. Deslattes 2/3, E.G. Kessler, G.L. Greene 2/3i A. Henins 2/3, R.E. LaVilla l/3i and M. Gutkosky 1/3. We have enjoyed visits from H. Borner and T. Manning, Institut Max Von Laue-Paul Langevin (ILL) and M. Tanaka, National Research Laboratory of Metrology (NRLM) . Our activities take place at NBS in lattice interferometry and x-ray spectra while Y-ray work is carried out at ILL in Grenoble and one-and two-electron spectroscopy has proceeded at the Max-Planck Institute for Nuclear Physics (MPIKP) in Heidelberg and at the Gesellschaft fur Schwer ionenforschung (GSI) outside of Darmstadt, where there are also effective collaborators (Reinholdt Schuch, MPIKP and Heinrich Beyer, GSI). Gravitational work carried out by Luther (2/3) aims to produce an improved value of G which has a measure of intrinsic interest, but in addition, confronts efforts to estimate this numeric a priori (Sternglass, 1984, Cohen, 1985). This work also aims to test equivalence of passive and active gravitational mass for alumina, silica and tungsten. Here there are also conflicts and questions (Stacey, et al. 1981, Jacobson, 1983). Current Activities - accomplishments; The biggest challenge confronting this whole area of work is the improbably large (lOo) apparent discrepancy between the 1975 NBS interferometr ic determination of a Si lattice spacing and that subse- quently reported by the Physikalisch-Technische Bundesanstalt (PTB). First priority and maximum effort have been given and applied to (respectively) this question. The experimental capabilities were re-established by last year with additional diagnostic interferometr ic channels added to control the dominant source of systematic error. As reported last year this system appeared to be operational and had demonstrated sensitivity and accuracy adequate to accomplish the needed correction factor measurements. Unfortunately, it was not 2 . noticed at that time that a fundamental conceptual error prevented these (otherwise adequate) interferometric signals from giving the information needed to accomplish the required corrections. A revised "path curvature" interferometer was designed, fabricated (by Continental Optical and Perkin Elmer) and installed. This system began to operate in September 1985 and should have yielded significant results by the time of the Panel meeting. Aside from the primary interferometric measurement, there is a need for rapid and sensitive intercomparison of lattice spacings among crystals having nearly the same lattice parameter. To address this need, a new goniometric facility was designed and built with major contributions from our long-term visitor Dr. M. Tanaka. Although x-ray sources are used, the classical limits on lattice parameter precision implied by x-ray wavelength spread are largely circumvented. As originally planned, this new facility, the DELTA-D (6d) machine, would have replaced the second generation x-ray interferometer experiment. It would have made use of the same x-ray sources, vibration isolated and temperature-controlled environment as well as computer controlled measurement apparatus. Because of the problems already noted above, this sequential model is no longer appropriate. We have therefore begun a process which should yield an independent 6d machine within the month prior to the meeting of this panel. This process involves establishing a new (and previously unplanned) vibration isolated and temperature controlled environment. It also involves providing dual x-ray sources not previously contemplated and appropriate computer controlled data acquisition facilities. The NBS-ILL precision gamma-ray wavelength facility has been significantly up-graded during the past year. This up-grade coincided with a
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