1,525,778 research outputs found
Towards Coherent Neutrino Detection Using Low-Background Micropattern Gas Detectors
The detection of low energy neutrinos ( few tens of MeV) via coherent
nuclear scattering remains a holy grail of sorts in neutrino physics. This
uncontroversial mode of interaction is expected to profit from a sizeable
increase in cross section proportional to neutron number squared in the target
nucleus, an advantageous feature in view of the small probability of
interaction via all other channels in this energy region. A coherent neutrino
detector would open the door to many new applications, ranging from the study
of fundamental neutrino properties to true "neutrino technology".
Unfortunately, present-day radiation detectors of sufficiently large mass (
1 kg) are not sensitive to sub-keV nuclear recoils like those expected from
this channel. The advent of Micropattern Gas Detectors (MPGDs), new
technologies originally intended for use in High Energy Physics, may soon put
an end to this impasse. We present first tests of MPGDs fabricated with
radioclean materials and discuss the approach to assessing their sensitivity to
these faint signals. Applications are reviewed, in particular their use as a
safeguard against illegitimate operation of nuclear reactors. A first
industrial mass production of Gas Electron Multipliers (GEMs) is succinctly
described.Comment: Presented at the 2002 IEEE Nuclear Science Symposium and Medical
Imaging Conference, Norfolk VA, November 10-16. Submitted to IEEE Tran. Nucl.
Sci. Five pages, eight figure
Critical Points in the Linear Sigma Model with Quarks
We employ a simple effective model to study the chiral dynamics of two
flavors of quarks at finite temperature and density. In particular, we
determine the phase diagram in the plane of temperature and baryon chemical
potential as a function of the pion mass. An interesting phase structure occurs
which results in zero, one or two critical points depending on the value of the
vacuum pion mass.Comment: 16 pages plus 5 figure
Far-field optical microscope with nanometer-scale resolution based on in-plane surface plasmon imaging
A new far-field optical microscopy technique capable of reaching
nanometer-scale resolution has been developed recently using the in-plane image
magnification by surface plasmon polaritons. This microscopy is based on the
optical properties of a metal-dielectric interface that may, in principle,
provide extremely large values of the effective refractive index n up to
100-1000 as seen by the surface plasmons. Thus, the theoretical diffraction
limit on resolution becomes lambda/2n, and falls into the nanometer-scale
range. The experimental realization of the microscope has demonstrated the
optical resolution better than 50 nm for 502 nm illumination wavelength.
However, the theory of such surface plasmon-based far-field microscope
presented so far gives an oversimplified picture of its operation. For example,
the imaginary part of the metal dielectric constant severely limits the
surface-plasmon propagation and the shortest attainable wavelength in most
cases, which in turn limits the microscope magnification. Here I describe how
this limitation has been overcome in the experiment, and analyze the practical
limits on the surface plasmon microscope resolution. In addition, I present
more experimental results, which strongly support the conclusion of extremely
high spatial resolution of the surface plasmon microscope.Comment: 23 pages, 9 figures, will be published in the topical issue on
Nanostructured Optical Metamaterials of the Journal of Optics A: Pure and
Applied Optics, Manuscript revised in response to referees comment
Weighted Density Functionals for Ferroelectric Materials
The weighted density approximation, its implementation and its application to
ferroelectric materials is discussed. Calculations are presented for several
perovskite oxides and related materials. In general the weighted density
approximation is found to be superior to either the local density or
generalized gradient approximation for the ground state. Electronic structures
are little changed. The linear response of the weighted density approximation
is calculated for the homogeneous electron gas, and found to be improved
relative to the local density result, but not in full agreement with existing
Monte Carlo data. It is shown that the agreement can be further improved by a
simple modification. Calculations of the ferroelectric soft mode in KNbO
suggest that the low temperature distortion is approximately 20% smaller than
indicated by existing experiments.Comment: 14 pages, 2 embedded figures, uses aipproc style. Contribution
submitted to the Fifth Williamsburg Workshop on First-Principles Calculations
for Ferroelectric
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