671 research outputs found
Self-consistent calculations of quadrupole moments of the first 2+ states in Sn and Pb isotopes
A method of calculating static moments of excited states and transitions
between excited states is formulated for non-magic nuclei within the Green
function formalism. For these characteristics, it leads to a noticeable
difference from the standard QRPA approach. Quadrupole moments of the first 2+
states in Sn and Pb isotopes are calculated using the self-consistent TFFS
based on the Energy Density Functional by Fayans et al. with the set of
parameters DF3-a fixed previously. A reasonable agreement with available
experimental data is obtained.Comment: 5 pages, 6 figure
Thermal QRPA with Skyrme interactions and supernova neutral-current neutrino-nucleus reactions
The Thermal Quasiparticle Random-Phase Approximation is combined with the
Skyrme energy density functional method (Skyrme-TQRPA) to study the response of
a hot nucleus to an external perturbation. For the sample nuclei, Fe and
Ge, the Skyrme-TQRPA is applied to analyze thermal effects on the
strength function of charge-neutral Gamow-Teller transitions which dominate
neutrino-nucleus reactions at ~MeV. For the relevant
supernova temperatures we calculate the cross sections for inelastic neutrino
scattering. We also apply the method to examine the rate of
neutrino-antineutrino pair emission by hot nuclei. The cross sections and rates
are compared with those obtained earlier from the TQRPA calculations based on
the phenomenological Quasiparticle-Phonon Model Hamiltonian. For inelastic
neutrino scattering on Fe we also compare the Skyrme-TQRPA results to
those obtained earlier from a hybrid approach that combines shell-model and RPA
calculations.Comment: Minor revisions according to referee's recomendation
Gamow-Teller strength distributions at finite temperatures and electron capture in stellar environments
We propose a new method to calculate stellar weak-interaction rates. It is
based on the Thermo-Field-Dynamics formalism and allows the calculation of the
weak-interaction response of nuclei at finite temperatures. The thermal
evolution of the GT distributions is presented for the sample nuclei Fe and ~Ge. For Ge we also calculate the strength distribution
of first-forbidden transitions. We show that thermal effects shift the GT
centroid to lower excitation energies and make possible negative- and
low-energy transitions. In our model we demonstrate that the unblocking effect
for GT transitions in neutron-rich nuclei is sensitive to increasing
temperature. The results are used to calculate electron capture rates and are
compared to those obtained from the shell model.Comment: 16 pages, 9 figure
Low-energy Dipole Excitations in Nuclei at the N=50,82 and Z=50 Shell Closures as Signatures for a Neutron Skin
Low-energy dipole excitations have been investigated theoretically in N=50,
several N=82 isotones and the Z=50 Sn isotopes. For this purpose a method
incorporating both HFB and multi-phonon QPM theory is applied. A concentration
of one-phonon dipole strength located below the neutron emission threshold has
been calculated in these nuclei. The analysis of the corresponding neutron and
proton dipole transition densities allows to assign a genuine pattern to the
low-energy excitations and making them distinct from the conventional GDR
modes. Analyzing also the QRPA wave functions of the states we can identify
these excitations as Pygmy Dipole Resonance (PDR) modes, recently studied also
in Sn and N=82 nuclei. The results for N=50 are exploratory for an experimental
project designed for the bremsstrahlung facility at the ELBE accelerator.Comment: Nuclear Physics in Astrophysics III Conference, 26 - 31 March 2007,
Forschungszentrum Dresden-Rossendorf, German
Weight functions of light shield and the signal at the input of optical sensor at the intersection of the bullets of light shield
In this article, the definition of weight functions of a light shield at the intersection of the bullet in different field areas of shield registration is considered. The signal definition at the input of an optical sensor at the intersection of the bullet of a light shield is viewed. The research results can be used in considering the facts that can influence on the error estimation of the coordinate determination when a bullet hits the target
Towards high-performance tubular-type protonic ceramic electrolysis cells with all-Ni-based functional electrodes
Protonic ceramic electrolysis cells (PCECs), which permit high-temperature electrolysis of water, exhibit various advantages over conventional solid oxide electrolysis cells (SOECs), including cost-effectiveness and the potential to operate at low-/intermediate-temperature ranges with high performance and efficiency. Although many efforts have been made in recent years to improve the electrochemical characteristics of PCECs, certain challenges involved in scaling them up remain unresolved. In the present work, we present a twin approach of combining the tape-calendering method with all-Ni-based functional electrodes with the aim of fabricating a tubular-designed PCEC having an enlarged electrode area (4.6 cm2). This cell, based on a 25 µm-thick BaCe0.5Zr0.3Dy0.2O3–δ proton-conducting electrolyte, a nickel-based cermet and a Pr1.95Ba0.05NiO4+δ oxygen electrode, demonstrates a high hydrogen production rate (19 mL min–1 at 600 °C), which surpasses the majority of results reported for traditional button- or planar-type PCECs. These findings increase the scope for scaling up solid oxide electrochemical cells and maintaining their operability at reducing temperatures. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of SciencesRussian Foundation for Basic Research, RFBR: 18-38-20063Council on grants of the President of the Russian FederationThis work was supported by the Russian Foundation for Basic Research (grant no. 18-38-20063 ). Dr. D. Medvedev is grateful to the Council of the President of the Russian Federation (scholarship no. СП−161.2018.1) for supporting the studies devoted to new MIEC materials. Other sections are performed within the framework of the budgetary plans of the Institute of High Temperature Electrochemistry
Population of isomers in decay of the giant dipole resonance
The value of an isomeric ratio (IR) in N=81 isotones (Ba, Ce,
Nd and Sm) is studied by means of the ( reaction.
This quantity measures a probability to populate the isomeric state in respect
to the ground state population. In ( reactions, the giant dipole
resonance (GDR) is excited and after its decay by a neutron emission, the
nucleus has an excitation energy of a few MeV. The forthcoming decay
by direct or cascade transitions deexcites the nucleus into an isomeric or
ground state. It has been observed experimentally that the IR for Ba
and Ce equals about 0.13 while in two heavier isotones it is even less
than half the size. To explain this effect, the structure of the excited states
in the energy region up to 6.5 MeV has been calculated within the Quasiparticle
Phonon Model. Many states are found connected to the ground and isomeric states
by , and transitions. The single-particle component of the wave
function is responsible for the large values of the transitions. The calculated
value of the isomeric ratio is in very good agreement with the experimental
data for all isotones. A slightly different value of maximum energy with which
the nuclei rest after neutron decay of the GDR is responsible for the reported
effect of the A-dependence of the IR.Comment: 16 pages, 4 Fig
Customized CMOS wavefront sensor
We report on an integrated Hartmann wavefront sensor (WFS) using passive-pixel architecture and pixels clustered as position-sensitive detectors for dynamic wavefront analysis. This approach substitutes a conventional imager, such as a CCD or CMOS imager, by a customized detector, thus improving the overall speed performance. CMOS (complementary-metal- oxide-semiconductor) technology enables on-chip integration of several analog and digital circuitry. The sensor performance depends on the feature size of the technology, noise levels, photosensitive elements employed, architecture chosen and reconstruction algorithm.(undefined
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