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ADVANCED MATERIALS & PROCESSES •
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alloys during solidification. The studies were complemented with local, higher resolu-
tion observations via synchrotron x-ray radiography, a technique that favors examina-
tion of small volumes (less than 1 mm
3
) and low-density metals. Proton radiography
enables direct observations of structural outcomes as a function of processing. It also
enables studies of 3D processes, such as fluid flow encountered during solidification for
which thick sections, rather than thin (constrained) sections, better represent processes
that occur in actual castings. This information bridges the micro- and macro- length
scale regimes and provides insight into solidification processes.
lanl.gov.NIST launches new U.S. time standard
The National Institute of Standards and Technology (NIST), Gaithersburg, Md.,
officially launched a new atomic clock, called NIST-F2, to serve as the new U.S. civil-
ian time and frequency standard, along with the current NIST-F1 standard. NIST-F2
would neither gain nor lose one second in about 300 million years, making it roughly
three times as accurate as NIST-F1, which has served as the standard since 1999. Both
clocks use a “fountain” of cesium atoms to determine the exact length of a second. NIST
scientists recently reported the first official performance data for NIST-F2, which has
been under development for a decade, to the International Bureau of Weights and
Measures (BIPM), located near Paris. That agency collates data from atomic clocks
around the world to produce Coordinated Universal Time, the international time stan-
dard. According to BIPM data, NIST-F2 is now the world’s most accurate time standard.
nist.gov.Physicists Steve Jefferts (foreground) and
Tom Heavner with the NIST-F2 “cesium
fountain” atomic clock, a new civilian time
standard for the U.S. Courtesy of NIST.