Fundamental Constants Data Center

Technical Highlights

• Measurement Uncertainty - 1994 Edition of NIST TN 1297. In collaboration with C.E. Kuyatt (formerly of the Physics Laboratory and now in the Director's Office), we prepared, published, and widely distributed a new edition of NIST Technical Note (TN) 1297, Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results. The first edition of TN 1297 was initially published in January 1993. A second printing followed shortly thereafter, and in total some 10,000 copies were distributed to individuals at NIST and in both the United States at large and abroad - to metrologists, scientists, engineers, statisticians, and others who are concerned with measurement and the evaluation and expression of the uncertainty of the result of a measurement.

  The 1994 edition of TN 1297 includes a new appendix - Appendix D - which clarifies and gives additional guidance on a number of topics related to measurement uncertainty, including the use of certain terms such as accuracy and precision. It was prepared in response to questions concerning some of the points the 1993 edition addressed and some it did not. Minor word changes were also made in a few portions of the text in order to recognize the official publication in October 1993 by the International Organization for Standardization (ISO) of the Guide to the Expression of Uncertainty in Measurement on which TN 1297 is based; and to bring TN 1297 into fuller harmony with the Guide. However, the NIST policy on measurement uncertainty, Statements of Uncertainty Associated with Measurement Results, which is reproduced as Appendix C of TN 1297, is unchanged.

  It is expected that the new appendix will make the 1994 edition of TN 1297 even more useful than its predecessor, the 1993 edition. To date, several thousand copies have been distributed throughout the world. These include copies to the NIST technical staff, to the members of the National Conference of Standards Laboratories, to the Members and Corresponding Members of the International Organization of Legal Metrology, to the Committee Delegates, Rapporteurs, and Contact Persons of EUROMET (a European collaboration in measurement standards) and of NORAMET (a North American regional collaboration in national measurement standards and services), and to the members of the Council on Optical Radiation Measurements and of the Council on Ionizing Radiation Measurements and Standards.
• Precision Measurement Grants. We awarded, on behalf of NIST, new Precision Measurement Grants to Kurt Gibble of Yale University and Luis Orozco of the State University of New York at Stony Brook. The grants are in the amount of $50,000 per year, renewable for two additional years. NIST sponsors these grants to promote fundamental research in measurement science in U.S. colleges and universities and to foster contacts between NIST scientists and researchers in the academic community actively engaged in such work.

  The aim of Gibble's project, "Laser-Cooled Atomic Clocks `without' Cold Collisions," is to first eliminate the frequency shifts due to collisions between laser-cooled atoms in an atomic fountain clock. To this end, ¹³³Cs, ¹³⁵Cs, ¹³⁷Cs, and ⁸⁷Rb fountains will be investigated. Work will then focus on using the optimal candidate to achieve the 10^-16 stability potential (for averaging times of less than 10⁴ s) of a laser cooled clock operating as a semicontinuous atomic fountain.

  The aim of Orozco's project, "Spectroscopy of Francium: Towards a Precise Parity Nonconservation Measurement in A Laser Trap," is to understand the spectroscopy of magneto-optically trapped radioactive francium atoms well enough to perform a precise test of the Standard Model of particle physics at low energy. The latter will be done by carrying out measurements of parity nonconserving transitions in francium, an ideal atom for such measurements because the parity nonconserving transition rate is 15 times larger than in the commonly used cesium atom, and the availability of many isotopes can make the interpretation of the results less sensitive to atomic theory calculations.