19,951 research outputs found
Reactor antineutrino spectra and their application to antineutrino-induced reactions. II
The antineutrino and electron spectra associated with various nuclear fuels are calculated. While there are substantial differences between the spectra of different uranium and plutonium isotopes, the dependence on the energy and flux of the fission-inducing neutrons is very weak. The resulting spectra can be used for the calculation of the antineutrino and electron spectra of an arbitrary nuclear reactor at various stages of its refueling cycle. The sources of uncertainties in the spectrum are identified and analyzed in detail. The exposure time dependence of the spectrum is also discussed. The averaged cross sections of the inverse neutron β decay, weak charged and neutral-current-induced deuteron disintegration, and the antineutrino-electron scattering are then evaluated using the resulting ν̅_e spectra.
[RADIOACTIVITY, FISSION 235U, 238U, (^239)Pu, (^240)Pu, (^241)Pu, antineutrino and electron spectra calculated. σ for ν̅ induced reactions analyzed.
Cavity-assisted spontaneous emission as a single-photon source: Pulse shape and efficiency of one-photon Fock state preparation
Within the framework of exact quantum electrodynamics in dispersing and
absorbing media, we have studied the quantum state of the radiation emitted
from an initially in the upper state prepared two-level atom in a high-
cavity, including the regime where the emitted photon belongs to a wave packet
that simultaneously covers the areas inside and outside the cavity. For both
continuing atom--field interaction and short-term atom--field interaction, we
have determined the spatio-temporal shape of the excited outgoing wave packet
and calculated the efficiency of the wave packet to carry a one-photon Fock
state. Furthermore, we have made contact with quantum noise theories where the
intracavity field and the field outside the cavity are regarded as
approximately representing independent degrees of freedom such that two
separate Hilbert spaces can be introduced.Comment: 16 pages, 7 eps figures; improved version as submitted to Phys. Rev.
Tomographic reconstruction of quantum states in N spatial dimensions
Most quantum tomographic methods can only be used for one-dimensional
problems. We show how to infer the quantum state of a non-relativistic
N-dimensional harmonic oscillator system by simple inverse Radon transforms.
The procedure is equally applicable to finding the joint quantum state of
several distinguishable particles in different harmonic oscillator potentials.
A requirement of the procedure is that the angular frequencies of the N
harmonic potentials are incommensurable. We discuss what kind of information
can be found if the requirement of incommensurability is not fulfilled and also
under what conditions the state can be reconstructed from finite time
measurements. As a further example of quantum state reconstruction in N
dimensions we consider the two related cases of an N-dimensional free particle
with periodic boundary conditions and a particle in an N-dimensional box, where
we find a similar condition of incommensurability and finite recurrence time
for the one-dimensional system.Comment: 8 pages, 1 figur
Final results from the Palo Verde Neutrino Oscillation Experiment
The analysis and results are presented from the complete data set recorded at
Palo Verde between September 1998 and July 2000. In the experiment, the
\nuebar interaction rate has been measured at a distance of 750 and 890 m
from the reactors of the Palo Verde Nuclear Generating Station for a total of
350 days, including 108 days with one of the three reactors off for refueling.
Backgrounds were determined by (a) the technique based on the difference
between signal and background under reversal of the positron and neutron parts
of the correlated event and (b) making use of the conventional reactor-on and
reactor-off cycles. There is no evidence for neutrino oscillation and the mode
\nuebar\to\bar\nu_x was excluded at 90% CL for \dm>1.1\times10^{-3} eV
at full mixing, and \sinq>0.17 at large \dm.Comment: 11 pages, 8 figure
Investigations of fast neutron production by 190 GeV/c muon interactions on different targets
The production of fast neutrons (1 MeV - 1 GeV) in high energy muon-nucleus
interactions is poorly understood, yet it is fundamental to the understanding
of the background in many underground experiments. The aim of the present
experiment (CERN NA55) was to measure spallation neutrons produced by 190 GeV/c
muons scattering on carbon, copper and lead targets. We have investigated the
energy spectrum and angular distribution of spallation neutrons, and we report
the result of our measurement of the neutron production differential cross
section.Comment: 19 pages, 11 figures ep
A simple model of reactor cores for reactor neutrino flux calculations for the KamLAND experiment
KamLAND is a reactor neutrino oscillation experiment with a very long
baseline. This experiment successfully measured oscillation phenomena of
reactor antineutrinos coming mainly from 53 reactors in Japan. In order to
extract the results, it is necessary to accurately calculate time-dependent
antineutrino spectra from all the reactors. A simple model of reactor cores and
code implementing it were developed for this purpose. This paper describes the
model of the reactor cores used in the KamLAND reactor analysis.Comment: 14 pages, 7 figures, submitted to Nuclear Instruments and Methods in
Physics Research
Overlap of QRPA states based on ground states of different nuclei --mathematical properties and test calculations--
The overlap of the excited states in quasiparticle random-phase approximation
(QRPA) is calculated in order to simulate the overlap of the intermediate
nuclear states of the double-beta decay. Our basic idea is to use the
like-particle QRPA with the aid of the closure approximation and calculate the
overlap as rigorously as possible by making use of the explicit equation of the
QRPA ground state. The formulation is shown in detail, and the mathematical
properties of the overlap matrix are investigated. Two test calculations are
performed for relatively light nuclei with the Skyrme and volume delta-pairing
energy functionals. The validity of the truncations used in the calculation is
examined and confirmed.Comment: 17 pages, 15 figures, full paper following arXiv:1205.5354 and Phys.
Rev. C 86 (2012) 021301(R
Control of the Casimir force by the modification of dielectric properties with light
The experimental demonstration of the modification of the Casimir force
between a gold coated sphere and a single-crystal Si membrane by light pulses
is performed. The specially designed and fabricated Si membrane was irradiated
with 514 nm laser pulses of 5 ms width in high vacuum leading to a change of
the charge-carrier density. The difference in the Casimir force in the presence
and in the absence of laser radiation was measured by means of an atomic force
microscope as a function of separation at different powers of the absorbed
light. The total experimental error of the measured force differences at a
separation of 100 nm varies from 10 to 20% in different measurements. The
experimental results are compared with theoretical computations using the
Lifshitz theory at both zero and laboratory temperatures. The total theoretical
error determined mostly by the uncertainty in the concentration of charge
carriers when the light is incident is found to be about 14% at separations
less than 140 nm. The experimental data are consistent with the Lifshitz theory
at laboratory temperature, if the static dielectric permittivity of
high-resistivity Si in the absence of light is assumed to be finite. If the dc
conductivity of high-resistivity Si in the absence of light is included into
the model of dielectric response, the Lifshitz theory at nonzero temperature is
shown to be experimentally inconsistent at 95% confidence. The demonstrated
phenomenon of the modification of the Casimir force through a change of the
charge-carrier density is topical for applications of the Lifshitz theory to
real materials in fields ranging from nanotechnology and condensed matter
physics to the theory of fundamental interactions.Comment: 30 pages, 10 figures, 2 table
Spin flip lifetimes in superconducting atom chips: BCS versus Eliashberg theory
We investigate theoretically the magnetic spin-flip transitions of neutral
atoms trapped near a superconducting slab. Our calculations are based on a
quantum-theoretical treatment of electromagnetic radiation near dielectric and
metallic bodies. Specific results are given for rubidium atoms near a niobium
superconductor. At the low frequencies typical of the atomic transitions, we
find that BCS theory greatly overestimates coherence effects, which are much
less pronounced when quasiparticle lifetime effects are included through
Eliashberg theory. At 4.2 K, the typical atomic spin lifetime is found to be
larger than a thousand seconds, even for atom-superconductor distances of one
micrometer. This constitutes a large enhancement in comparison with normal
metals.Comment: 10 pages, 4 figure
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