Fundamental Constants Data Center

Technical Highlights

• Guide to the Expression of Uncertainty. In 1991, the FCDC, in collaboration with C.E. Kuyatt, also of the Physics Laboratory, assumed primary responsibility for preparing the ISO "Guide to the Expression of Uncertainty in Measurement." The Guide was developed under the auspices of ISO Technical Advisory Group 4 (TAG 4), Metrology, and was undertaken at the request of the International Committee for Weights and Measures (CIPM). After many drafts of the 100-plus page document, including one for which some 2000 copies were circulated worldwide for comment, the final version was published by ISO in October 1993, in the name of the seven international organizations that sponsored its development: the International Bureau of weights and Measures (BIPM), the International Electrotechnical Commission (IEC), the International Federation of Clinical Chemistry (IFCC), ISO, the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Pure and Applied Physics (IUPAP), and the International Organization of Legal Metrology (OIML).

  The Guide, whose publication is the culmination of a 16-year effort to reach an international consensus on expressing measurement uncertainty, represents the current international view of how to express measurement uncertainty based on the approach recommended by the CIPM in 1981. The CIPM approach has already been adopted by many organizations, including NIST, the Western European Calibration Cooperation (WECC), EUROMET (an organization which coordinates the work of European national standards laboratories), the National Conference of Standards Laboratories (NCSL), and several large U.S. companies, and the publication of the Guide is expected to give further impetus to the worldwide adoption of that approach.

  In addition, the FCDC, again together with C.E. Kuyatt, published in January 1993 NIST Technical Note 1297, "Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results." Technical Note 1297 succinctly summarizes the most important aspects of the ISO Guide and was prepared to help the NIST staff put into practice the new NIST policy on statements of uncertainty associated with measurement results. This policy, which is based on the CIPM approach and is reprinted as Appendix C of TN 1297, was adopted by NIST in October 1992 and is now almost completely implemented. To foster the widespread adoption of the CIPM approach to expressing measurement uncertainty, the FCDC has distributed hundreds of copies of the Guide and thousands of copies of NIST TN 1297. A number of talks about these documents have also been given to a variety of interested groups.

• Precision Measurement Grants. The FCDC awarded, on behalf of NIST,new Precision Measurement Grants to Mark Kasevich of Stanford University and Ronald Walsworth, Smithsonian Astrophysical Laboratory, Harvard Smithsonian Center for Astrophysics. The grants are in the amount of $50,000 per year, renewable for two additional years.

  The aim of Kasevich's project, "Development of an Atom Interferometer Gyroscope for Tests of General Relativity," is to develop significantly improved atom interferometers based on slowed and cooled cesium atomic beams and to use the interferometers to construct a high-precision rotation sensor. The motivation for the work is the possibility of achieving levels of sensitivity high enough to observe general relativistic effects. The goal for the 3-year time period of the NIST grant is to demonstrate a sensitivity to rotations of better than 10^-11 (rad/s)/Hz^1/2.

  Walsworth's project, "Development of a Dual Noble Gas Laser for Use in a Test of Time Reversal Invariance," involves building a newly conceived device,a dual noble-gas maser consisting of cohabitating ensembles of ³He and ¹²⁹Xe atoms each performing an active, steady-state maser oscillation. The device will be used for a 10-fold improvement test of time reversal invariance by searching for a permanent electric dipole moment (PEDM) of the ¹²⁹Xe atom. The ³He maser will serve as a precision magnetometer to control the system's magnetic field, while the ¹²⁹Xe is used to search for a PEDM.