2,056 research outputs found
Long-Term Testing and Properties of Acrylic for the Daya Bay Antineutrino Detectors
The Daya Bay reactor antineutrino experiment has recently measured the
neutrino mixing parameter sin22{\theta}13 by observing electron antineutrino
disappearance over kilometer-scale baselines using six antineutrino detectors
at near and far distances from reactor cores at the Daya Bay nuclear power
complex. Liquid scintillator contained in transparent target vessels is used to
detect electron antineutrinos via the inverse beta-decay reaction. The Daya Bay
experiment will operate for about five years yielding a precision measurement
of sin22{\theta}13. We report on long-term studies of poly(methyl methacrylate)
known as acrylic, which is the primary material used in the fabrication of the
target vessels for the experiment's antineutrino detectors. In these studies,
acrylic samples are subjected to gaseous and liquid environmental conditions
similar to those experienced during construction, transport, and operation of
the Daya Bay acrylic target vessels and detectors. Mechanical and optical
stability of the acrylic as well as its interaction with detector liquids is
reported.Comment: 17 pages, 13 figures Submitted to JINS
Search for Sterile Neutrinos with a Radioactive Source at Daya Bay
The far site detector complex of the Daya Bay reactor experiment is proposed
as a location to search for sterile neutrinos with > eV mass. Antineutrinos
from a 500 kCi 144Ce-144Pr beta-decay source (DeltaQ=2.996 MeV) would be
detected by four identical 20-ton antineutrino targets. The site layout allows
flexible source placement; several specific source locations are discussed. In
one year, the 3+1 sterile neutrino hypothesis can be tested at essentially the
full suggested range of the parameters Delta m^2_{new} and sin^22theta_{new}
(90% C.L.). The backgrounds from six nuclear reactors at >1.6 km distance are
shown to be manageable. Advantages of performing the experiment at the Daya Bay
far site are described
Recombination in polymer-fullerene bulk heterojunction solar cells
Recombination of photogenerated charge carriers in polymer bulk
heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and
the fill factor (FF). Identifying the mechanism of recombination is, therefore,
fundamentally important for increasing the power conversion efficiency. Light
intensity and temperature dependent current-voltage measurements on polymer BHJ
cells made from a variety of different semiconducting polymers and fullerenes
show that the recombination kinetics are voltage dependent and evolve from
first order recombination at short circuit to bimolecular recombination at open
circuit as a result of increasing the voltage-dependent charge carrier density
in the cell. The "missing 0.3V" inferred from comparison of the band gaps of
the bulk heterojunction materials and the measured open circuit voltage at room
temperature results from the temperature dependence of the quasi-Fermi-levels
in the polymer and fullerene domains - a conclusion based upon the fundamental
statistics of Fermions.Comment: Accepted for publication in Physical Review B.
http://prb.aps.org/accepted/B/6b07cO3aHe71bd1b149e1425e58bf2868cda2384d?ajax=1&height=500&width=50
Constraining the Leading Weak Axial Two-body Current by SNO and Super-K
We analyze the Sudbury Neutrino Observatory (SNO) and Super-Kamiokande (SK) data on charged current (CC), neutral current (NC) and neutrino electron elastic scattering (ES) reactions to constrain the leading weak axial two-body current parameterized by L_1A. This two-body current is the dominant uncertainty of every low energy weak interaction deuteron breakup process, including SNO's CC and NC reactions. Our method shows that the theoretical inputs to SNO's determination of the CC and NC fluxes can be self-calibrated, be calibrated by SK, or be calibrated by reactor data. The only assumption made is that the total flux of active neutrinos has the standard ^8B spectral shape (but distortions in the electron neutrino spectrum are allowed). We show that SNO's conclusion about the inconsistency of the no-flavor-conversion hypothesis does not contain significant theoretical uncertainty, and we determine the magnitude of the active solar neutrino flux
Dimerization structures on the metallic and semiconducting fullerene tubules with half-filled electrons
Possible dimerization patterns and electronic structures in fullerene tubules
as the one-dimensional pi-conjugated systems are studied with the extended
Su-Schrieffer-Heeger model. We assume various lattice geometries, including
helical and nonhelical tubules. The model is solved for the half-filling case
of -electrons. (1) When the undimerized systems do not have a gap, the
Kekule structures prone to occur. The energy gap is of the order of the room
temperatures at most and metallic properties would be expected. (2) If the
undimerized systems have a large gap (about 1eV), the most stable structures
are the chain-like distortions where the direction of the arranged
trans-polyacetylene chains is along almost the tubular axis. The electronic
structures are ofsemiconductors due to the large gap.Comment: submitted to Phys. Rev. B, pages 15, figures 1
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