Number 193, September 6, 1994 by Phillip F. Schewe and Ben Stein
IMPROVED MASS VALUES FOR NINE ELEMENTS AND FOR THE NEUTRON have been
published by an MIT research team, opening possibilities for a truly fundamental
definition of the kilogram as well as the most precise direct test yet
of Einstein's equation E=mc**2. The new mass values, for elements such
as hydrogen, deuterium, and oxygen-16, are 20-1000 times more accurate
than previous ones, with uncertainties in the range of 100 parts per trillion.
To determine the masses, the MIT team, led by David Pritchard (617-253-6812),
traps single ions in electric and magnetic fields and obtains each ion's
mass-to-charge ratio by measuring its cyclotron frequency, the rate at
which it circles about in the magnetic field. The trapped ions, in general,
are charged molecules containing the atoms of interest, and from their
measurements the researchers can extract values for individual atomic masses.
One important atom in the MIT mass table is silicon-28. With the new mass
value and comparably accurate measurements of the density and the lattice
spacing of ultrapure Si-28 (see Update 178), a new fundamental definition
of the kilogram (replacing the kilogram artifact in Paris) could be possible.
The MIT team also plans to participate in a test of E=mc**2 by using its
mass values of nitrogen-14, nitrogen-15, and a neutron. When N-14 and a
neutron combine, the resulting N-15 atom is not as heavy as the sum of
its parts, because it converts some of its mass into energy by releasing
gamma rays. In an upcoming experiment in Grenoble, France there are plans
to measure the "E" side of the equation by making highly accurate
measurements of these gamma rays. (F. DeFilippo et al, Physical Review
Letters, 12 September.)
A QUASAR-LIKE OBJECT has been discovered in our galaxy. Using the Very
Large Array radio telescope to monitor emissions from GRS 1915+105, astronomers
have observed jets of matter shooting out at a velocity close to the speed
of light. Somewhat resembling the enigmatic object SS433, discovered in
the 1970s, the higher-energy GRS 1915+105 is also thought to be a double-star
system. (Nature, 1 September.)
THE PEER REVIEW PROCESS, as it pertains to grant applications at large
federal agencies such as the National Science Foundation, has received
a favorable audit from the Government Accounting Office (GAO). Notwithstanding
periodic complaints about various perceived biases, a new GAO report finds
that factors such as an applicant's geographical location, his academic
rank, and his department's prestige, are largely not related to the subsequent
review score. Application reviewers from elite institutions seem actually
to be underrepresented relative to the number of applicants from those
same institutions. (Copies of the report, GAO/PEMD-94-1, can be requested
by calling 202-512-6000.)
CORRECTION: Charles Rhodes, not Charles Townes, has been conducting
research at the University of Illinois at Chicago on the excitation of
x rays from atomic clusters (Update 192).
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