[tt] Physics News Update 855

Tue Feb 5 16:07:59 UTC 2008

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From: physnews at aip.org
Date: Tue, 5 Feb 2008 10:12:42 -0500
To: eugen at LEITL.ORG
Subject: Physics News Update 855
Reply-to: physnews at aip.org

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 855   February 4, 2008      www.aip.org/pnu
by Phillip F. Schewe and Jason S. Bardi

THE DARKEST MATERIAL EVER MADE consists of a carpet of vertically
oriented carbon nanotubes.  The darkness or lightness of any object
depends on the fraction of light falling on the object that gets
reflected back.  The reflectivity of the nanotube array developed by
physicists at the Rensselaer Polytechnic Institute (RPI) is only
0.045%, three times smaller than the best previous dark object (see
figure at <http://www.aip.org/png/2008/296.htm>).  Shawn Lin and his
colleagues grow the nanotubes on iron nanodots atop a silicon
wafer.  The resulting mat is thin (10-800 microns) and lightweight
(.01-.02 g/cm^3).
Possible applications include the revision of darkness standards,
such as are used by photographers.  The lowest dark scale defined by
NIST right now is for reflectances of about 1.5%.  The material
might also be useful in astronomical detectors (where you want to
soak up stray radiation) or in photovoltaic cells which turn
sunlight into electricity.  Lin (sylin at rpi.edu) says that an
additional feature of this new material is that it represents a
controllably porous substance with an index of refraction (1.02) not
very different from that of air.  (Yang et al., NanoLetters, 9
January 2008)

ANTI-NEUTRINOS AND NONPROLIFERATION.  A new compact detector may
help international inspectors peer inside a working nuclear reactor
in a non-intrusive way by directly measuring the flux of
anti-neutrinos coming out.  Since their first use, nuclear reactors
have, at least in principle, been closely related with nuclear
weapons.  For example, reactors produce plutonium which can later be
fashioned into bomb material.  The question of how to monitor the
actual operation of a particular reactor and compare the changing
plutonium inventory to what is expected from normal operations
(producing electric power, say) is a large component of nuclear
non-proliferation efforts.
The cubic-meter-scale detector, proposed by Adam Bernstein, leader
of the Advanced Detectors Group at Lawrence Livermore National
Laboratory (925-422-5918, bernstein3 at llnl.gov) and built by a team
from Livermore and Sandia National Laboratories California branch,
would not attempt to monitor the reactor*s performance on a moment
by moment basis.  Instead its sensitivity is more attuned to the
number of antineutrinos produced over hourly, daily and weeklong
intervals. These time scales, Bernstein says, are well suited to the
kind of monitoring performed by the International Atomic Energy
Agency (IAEA). The detector built by the LLNL/SNL collaboration
operates unattended for long periods without significant
maintenance, is self-calibrating, and does not affect plant
operations in any way (see illustration of a detector at work,
http://www.aip.org/png/2008/295.htm ). Data from the detector is
acquired remotely in real time. The detector module can be made
tamper-proof using standard techniques, and the anti-neutrino
signature seen by the detector (the arrival of a positron followed
30 microseconds later by a neutron) is hard to mimic with surrogate
neutron or gamma sources. In conjunction with knowledge of the input
fuel load and core design, the observed anti-neutrino flux provides
a direct measure of the reactor*s power and isotopic content.
(Bernstein et al., Applied Physics Letters, upcoming article)

PHYSICAL REVIEW LETTERS celebrates its fiftieth anniversary this
year.  Several special events are planned, such as sessions at the
upcoming March and April APS meetin
gs.  Also, a number of famous PRL
papers from the past half century are being made available on the
following website: <http://prl.aps.org/50years/milestones> along
with a brief summary of the papers* importance.

***********
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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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