1995/1996 Technical Highlights
- Guide for the Use of the SI - 1995 Edition of NIST SP 811. We
prepared, published, and widely distributed a new edition of NIST Special
Publication (SP) 811, Guide for the
Use of the International System of Units (SI).
The 1995 edition of SP 811 corrects a number of misprints in the 1991 edition
(prepared by A.O. McCoubrey), incorporates a significant amount of
additional material intended to answer frequently asked questions concerning
the SI and SI usage, and updates the bibliography. The added material includes
a check list for reviewing the consistency of written documents with the SI.
Some changes in format have also been made in an attempt to improve the ease
of use of SP 811.
To date, nearly 15,000 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), to the
members of the Council on Optical Radiation Measurements and of the Council on
Ionizing Radiation Measurements and Standards, and to numerous readers of many
different trade magazines, newsletters, technical journals, etc. SP 811
is also available on the WWW home page of the Physics Laboratory.
- Precision Measurement Grants. We awarded, on behalf of NIST, new
Precision Measurement Grants to Siu Au Lee of Colorado State
University and Jonathan Sapirstein of the University of Notre Dame. 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 Sui Au Lee's project is to directly measure, for the first
time, the birefringence of light propagating in vacuum in a strong magnetic
field, and to conduct an improved laboratory search for axions. This work
is based on the prediction that when a beam of light travels in vacuum in
a strong applied magnetic field, the quantum electrodynamic (QED) vacuum
polarization induces a small change in the index of refraction of the vacuum.
Because the index change depends on the polarization of the beam relative
to the direction of the field, the vacuumacquires a birefringence. Although
this QED effect has never been observed, the recent development of long,
high-field superconducting magnets and the progress made in developing
low-loss mirrors for laser gyroscopes and laser gravitational detectors
has now made its observation feasible. This is a unique opportunity to carry
out a new test of QED, the most accurate theory of modern physics.
The aim of Sapirstein's project is to improve the theory of the energy levels
of atomic helium. Accurate measurements of various energy levels of helium and
helium-like ions have been and are continuing to be carried out. Of particular
interest are recent measurements of the fine structure of helium with a
relative standard uncertainty of 1 × 10-7, and their
expected significant improvement. These can be used to determine one of
nature's most important fundamental constants, the fine-structure constant
α, provided the theory has a comparable uncertainty. One of Sapirstein's
goals is to extend the existing Bethe-Salpeter equation calculations, which
include all corrections of order α2 relative to the fine
structure, to all corrections of order α3. When the
α3 corrections are known, a value of α will be available
from helium that can be compared with values obtained from the quantum Hall
effect (QHE); and from the quantum electrodynamic (QED) theory of the magnetic
moment anomaly of the electron ae and its experimental
determination. This will provide a new, critical check on the theory of the
QHE and of the internal consistency of QED.
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