Technical Highlights
- New Values of the Constants. At midnight on 23 July 1999, the new
1998 self-consistent set of over 300 values of the basic fundamental constants
and conversion factors of physics and chemistry recommended by CODATA first
became available for world-wide use at the FCDC Web site
physics.nist.gov/cuu. The new set is the result
of the 1998 CODATA least-squares adjustment of the values of the constants
carried out by P.J. Mohr and B.N. Taylor of the Physics Laboratory
under the auspices of the CODATA Task Group on Fundamental Constants. Based on
all of the data available through 31 December 1998, the new set replaces its
immediate predecessor recommended by CODATA in 1986. Because of the new values,
the FCDC Web site received over 200,000 hits in October 1999 alone.
- New Precision Measurement Grants. Two new NIST Precision Measurement
Grants in the amount of $50,000 were awarded for fiscal year 2000 to Prof.
E.G. Gwinn of the University of California (Santa Barbara) and Prof.
P. Majumder of Williams College. The aim of Gwinn’s project,
"Combining the Quantum Hall and AC Josephson Effects for Electric Current
Metrology," is to develop a new quantum standard of electric current by
combining the ac Josephson effect and the quantum Hall effect in an integrated,
unique way. The aim of Majumder’s project, "New Search for T-Violating
Forces in Atomic Thallium," is to develop a high-finesse laser ring-cavity
and to use it to search for long-range, electron-nucleon forces in atomic
thallium that violate time-reversal symmetry (T) but conserve
parity (P).
- Redefinition of the Kilogram. Motivated by recent NIST advances in
determining the Planck constant h using a moving-coil watt balance,
B.N. Taylor and P.J. Mohr considered the question of redefining the
kilogram in such a way that the value of h would be fixed, thereby
allowing a watt balance to be used to directly calibrate unknown standards of
mass [see Metrologia 36, 63 (1999)]. The proposed definition, analogous
to the present definition of the meter which has the effect of fixing the value
of the speed of light in vacuum c, is "The kilogram is the mass of
a body at rest whose equivalent energy equals the energy of a collection of
photons whose frequencies sum to
135 639 274 × 1042 Hz." Based on the
equations E = mc2
and E = h ν, this definition implies
h = 6.626 068 9 ... ×
10-34 J s. Such a definition would eliminate the last
material artifact from the SI and would allow any laboratory in the world that
was so inclined to realize the unit of mass in the SI.
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