Angular Momentum Dependence Research Articles

FUSION BY DIFFUSION MODEL REVISITED

A complete set of 27 excitation functions for synthesis of superheavy nuclei produced in cold fusion reactions was analyzed in terms of the "Fusion by Diffusion Model" of Światecki et al., modified to account for the angular momentum dependence of the fusion hindrance factor. The data on cold fusion reactions originate from experiments carried out at GSI Darmstadt, RIKEN Tokyo and LBNL Berkeley in which 208 Pb and 209 Bi targets were bombarded with the variety of projectiles ranging from 48,50 Ti to 70 Zn .

Rovibrational spectra of ammonia. I. Unprecedented accuracy of a potential energy surface used with nonadiabatic corrections

In this work, we build upon our previous work on the theoretical spectroscopy of ammonia, NH(3). Compared to our 2008 study, we include more physics in our rovibrational calculations and more experimental data in the refinement procedure, and these enable us to produce a potential energy surface (PES) of unprecedented accuracy. We call this the HSL-2 PES. The additional physics we include is a second-order correction for the breakdown of the Born-Oppenheimer approximation, and we find it to be critical for improved results. By including experimental data for higher rotational levels in the refinement procedure, we were able to greatly reduce our systematic errors for the rotational dependence of our predictions. These additions together lead to a significantly improved total angular momentum (J) dependence in our computed rovibrational energies. The root-mean-square error between our predictions using the HSL-2 PES and the reliable energy levels from the HITRAN database for J = 0-6 and J = 7∕8 for (14)NH(3) is only 0.015 cm(-1) and 0.020∕0.023 cm(-1), respectively. The root-mean-square errors for the characteristic inversion splittings are approximately 1∕3 smaller than those for energy levels. The root-mean-square error for the 6002 J = 0-8 transition energies is 0.020 cm(-1). Overall, for J = 0-8, the spectroscopic data computed with HSL-2 is roughly an order of magnitude more accurate relative to our previous best ammonia PES (denoted HSL-1). These impressive numbers are eclipsed only by the root-mean-square error between our predictions for purely rotational transition energies of (15)NH(3) and the highly accurate Cologne database (CDMS): 0.00034 cm(-1) (10 MHz), in other words, 2 orders of magnitude smaller. In addition, we identify a deficiency in the (15)NH(3) energy levels determined from a model of the experimental data.

Lattice QCD Towards Nuclear Forces

Recent studies of nuclear forces based on lattice QCD are presented. Not only the central potential but also the tensor potential is deduced from the Nambu–Bethe–Salpeter wave function measured with lattice QCD. This method is applied to various kinds of nuclear potentials, such as \({V_{NN}, V_{\Lambda N}, V_{p{\Xi}^0},V_{\Lambda\Lambda-N\Xi-\Sigma\Sigma}}\) (coupled-channel potential), and \({V^{\{{\bf {27},{8}_s,{1},{10},\overline{10},{8}_a}\}}}\) (flavor representation potential). The energy dependence and the angular momentum dependence of the quenched V NN is studied. A challenge for three-nucleon force from lattice QCD is also presented.

G factors of nuclear low-lying states: A covariant description

The g factors and spectroscopic quadrupole moments of low-lying excited states 21+, …, 81+ in 24Mg are studied in a covariant density functional theory. The wave functions are constructed by configuration mixing of axially deformed mean-field states projected on good angular momentum. The mean-field states are obtained from the constraint relativistic point-coupling model plus BCS calculations using the PC-F1 parametrization for the particle-hole channel and a density-independent delta-force for the particle-particle channel. The available experimental g factor and spectroscopic quadrupole moment of 21/+ state are reproduced quite well. The angular momentum dependence of g factors and spectroscopic quadrupole moments, as well as the effects of pairing correlations are investigated.

Sub-barrier capture with quantum diffusion approach

With the quantum diffusion approach the behavior of capture cross sections and mean-square angular momenta of captured systems are revealed in the reactions with deformed and spherical nuclei at sub-barrier energies. With decreasing bombarding energy under the barrier the external turning point of the nucleus-nucleus potential leaves the region of short-range nuclear interaction and action of friction. Because of this change of the regime of interaction, an unexpected enhancement of the capture cross section is found at bombarding energies far below the Coulomb barrier. This effect is shown its worth in the dependence of mean-square angular momentum on the bombarding energy. From the comparison of calculated capture cross sections and experimental capture or fusion cross sections the importance of quasifission near the entrance channel is demonstrated for the actinidebased reactions and reactions with medium-heavy nuclei at extreme sub-barrier energies.

Skew Scattering Mechanism by an Ab Initio Approach: Extrinsic Spin Hall Effect in Noble Metals

We present a first-principles study of the extrinsic spin Hall effect due to skew scattering at substitutional defects in noble metals (Cu, Ag, and Au). The dependence of the spin Hall angle on the type of impurity atoms in the host materials is discussed. We perform a detailed analysis based on the consideration of the total angular momentum dependence on scattering phase shifts of the impurity and host atoms.

THE IMPACT OF HOT JUPITERS ON THE SPIN-DOWN OF THEIR HOST STARS

We present a numerical Magnetohydrodynamic (MHD) study of the dependence of stellar mass and angular momentum- loss rates on the orbital distance to close-in giant planets. We find that the mass loss rate drops by a factor of $\approx$1.5-2, while the angular momentum loss rate drops by a factor of $\approx$4 as the distance decreases past the Alfv\'en surface. This reduction in angular momentum loss is due to the interaction between the stellar and planetary Alfv\'en surfaces, which modifies the global structure of the stellar corona and stellar wind on the hemisphere facing the planet, as well as the opposite hemisphere. The simulation also shows that the magnitude of change in angular momentum loss rate depends mostly on the strength of the planetary magnetic field and not on its polarity. The interaction however, begins at greater separation if the overall field topology of the star and the planet are of anti-aligned. Our results are consistent with evidence for excess angular momentum in stars harboring close-in giant planets, and show that the reduction in wind-driven angular momentum loss can compete with, and perhaps dominate, spin-up due to tidal interaction.

Shape resonances in ground-state diatomic molecules: General trends and the example of RbCs

The presence of shape resonances due to tunneling through the centrifugal barrier modifies strongly the dynamics of cold atom scattering. As shown on the example of the ground and lowest triplet electronic states of the {sup 85}Rb{sup 133}Cs molecule, the crucial parameter is, as usual for cold collisions, the scattering length. A general description of shape resonances of diatomic molecules is given from three simple single channel asymptotic models, whose respective performances are discussed. The first model, which consists of a R{sup -6} potential limited at short range by a repulsive wall, positioned to reproduce the s-wave scattering length, accounts satisfactorily for the main system-independent properties of shape resonances. Introduction in the model of energy- and angular-momentum-dependent nodal lines specific to the inner part of the potential greatly improves its efficiency. When the energy and angular momentum dependence of the nodal lines cannot be deduced from full potential calculations or from experiment, a rough, but universal, estimate of these properties is obtained by extending the R{sup -6} behavior of the potential up to the origin.

Systematic description of evaporation spectra for light and heavy compound nuclei

To systematically describe evaporation spectra for light and heavy compound nuclei over a large range of excitation energies, it was necessary to consider three ingredients in the statistical model. First, transmission coefficients or barrier penetration factors for charged-particle emission are typically taken from global fits to elastic-scattering data. However, such transmission coefficients do not reproduce the barrier region of evaporation spectra and reproduction of the data requires a distributions of Coulomb barriers. This is possibly associated with large fluctuations in the compound-nucleus shape or density profile. Second, for heavy nuclei, an excitation-energy dependent level-density parameter is required to describe the slope of the exponential tails of these spectra. The level-density parameter was reduced at larger temperatures, consistent with the expected fadeout of long-range correlation, but the strong $A$ dependence of this effect is unexpected. Last, to describe the angular-momentum dependence of the level density in light nuclei at large spins, the macroscopic rotational energy of the nucleus has to be reduced from the values predicted with the finite-range liquid-drop model.

Unusual features of proton and α-spectra from low-energy heavy-ion reactions

Proton and α-particle spectra have been measured in low-energy 12C and 16O-induced reactions on Nb and Y targets with the primary aim of measuring the excitation energy and angular momentum dependence of nuclear level density. In the γ-multiplicity gated spectra, an unusual feature of a broad structure at high particle energies is observed in all the cases. In the case of proton spectra, the structures have compound nuclear origin and point towards an excitation energy and angular momentum-dependent enhancement which is beyond the conventional level density prescription. The broad structures in the α-spectra cannot be fully explained within the statistical model even with the enhanced level density. In this case, other reaction mechanisms like the transfer of α or 8Be to the target could also be important.

Inhomogeneous and intrinsic damping of giant dipole resonance in hot rotating nuclei with A ∼ 150

High-energy gamma rays in the range of ∼4–28 MeV were measured in the reaction 28Si+124Sn at E(28Si) ∼ 185 MeV in coincidence with low-energy gamma ray multiplicities and evaporation residues. The centroid energy and width of the giant dipole resonance were extracted for various multiplicity windows from the statistical model analysis. These extracted widths, along with those from an earlier measurement at E(28Si) ∼ 149 MeV, show a discrepancy with the results of a calculation under the thermal shape fluctuation model which describes the inhomogeneous damping of the resonance. An empirical form of the temperature and angular momentum dependence of the width, describing the data at both the beam energies, has been derived. The present results suggest that the contributions from both the inhomogeneous damping and the intrinsic collisional damping processes should be included.

Formation of differential rotation in a cylindrical fluid layer

The formation of differential rotation observed in a rotating cylindrical layer heated locally is considered. Simulations have been done for different values of control parameters such as the geometry of a model (layer height, radius and heating area), the kinematic viscosity, the heat flux and the angular velocity of a cylinder. The integral characteristics of differential rotation are presented. The dependence of the relative angular momentum of the layer on different parameters has been studied.

Spin and orbital angular momentum of a class of nonparaxial light beams having a globally defined polarization

It is shown that the momentum density of free electromagnetic field splits into two parts. One has no contribution to the net momentum due to the transversality condition. The other yields all the momentum. The angular momentum that is associated with the former part is spin, and the angular momentum that is associated with the latter part is orbital angular momentum. Expressions for the spin and orbital angular momentum are given in terms of the electric vector in reciprocal space. The spin and orbital angular momentum defined this way are used to investigate the angular momentum of nonparaxial beams that are described in a recently published paper [Phys. Rev. A 78, 063831 (2008)]. It is found that the orbital angular momentum depends, apart from an $l$-dependent term, on two global quantities, the polarization represented by a generalized Jones vector and a new characteristic represented by a unit vector $\mathbf{I}$, though the spin depends only on the polarization. The polarization dependence of orbital angular momentum through the impact of $\mathbf{I}$ is obtained and discussed. Some applications of the result obtained here are also made. The fact that the spin originates from the momentum density that has no contribution to the net momentum is used to show that there does not exist the paradox on the spin of circularly polarized plane wave. The polarization dependence of both spin and orbital angular momentum is shown to be the origin of conversion from the spin of a paraxial Laguerre-Gaussian beam into the orbital angular momentum of the focused beam through a high numerical aperture.

Temperature and angular momentum dependence of the quadrupole deformation in sd-shell

Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for 28Si and 27Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard universal sd-shell (USD) interaction and the canonical partition function constructed from the calculated eigensolutions. It is shown that the extracted average quadrupole moments show a transitional behaviour as a function of temperature and the infered transitional temperature is shown to vary with angular momentum. The quadrupole deformation of the individual eigenstate is also analysed.

Angular momentum dependence of the nuclear level-density parameter aroundZ~50

\ensuremath{\alpha}-particle evaporation spectra and $\ensuremath{\gamma}$-ray multiplicities were measured for various target-projectile systems corresponding to residual nuclei in the range of ${Z}_{R}=48\text{\ensuremath{-}}55$ and with excitation energy in the range of 30--40 MeV. The high-energy part of the evaporation spectra were analyzed using the statistical model code PACE2 to derive values of the inverse level-density parameter $(K)$. The $K$ values were found to be in the range of 9.0--10.5 for all systems. Angular momentum dependence of the inverse level-density parameter was investigated using the $\ensuremath{\gamma}$-ray multiplicity data. It is seen that there are strong variations in $K$ as a function of angular momentum for many systems. Present results provide important input information for a systematic understanding of the statistical properties of nuclei at moderate excitation energies and angular momenta.

On the gravitational angular momentum of rotating sources

The gravitational energy-momentum and angular momentum satisfy the algebra of the Poincare group in the full phase space of the teleparallel equivalent of general relativity. The expression for the gravitational energy-momentum may be written as a surface integral in the three-dimensional spacelike hypersurface, whereas the definition for the angular momentum is given by a volume integral. It turns out that in practical calculations of the angular momentum of the gravitational field generated by localized sources like rotating neutron stars, the volume integral reduces to a surface integral, and the calculations can be easily carried out. Similar to previous investigations in the literature, we show that the total angular momentum is finite provided a certain asymptotic behaviour is verified. We discuss the dependence of the gravitational angular momentum on the frame, and argue that it is a measure of the dragging of inertial frames.

Angular Momentum Accretion onto a Gas Giant Planet

We investigate the accretion of angular momentum onto a protoplanet system using three-dimensional hydrodynamical simulations. We consider a local region around a protoplanet in a protoplanetary disk with sufficient spatial resolution. We describe the structure of the gas flow onto and around the protoplanet in detail. We find that the gas flows onto the protoplanet system in the vertical direction crossing the shock front near the Hill radius of the protoplanet, which is qualitatively different from the picture established by two-dimensional simulations. The specific angular momentum of the gas accreted by the protoplanet system increases with the protoplanet mass. At Jovian orbit, when the protoplanet mass M_p is M_p 1 M_J. The stronger dependence of the specific angular momentum on the protoplanet mass for M_p < 1 M_J is due to thermal pressure of the gas. The estimated total angular momentum of a system of a gas giant planet and a circumplanetary disk is two-orders of magnitude larger than those of the present gas giant planets in the solar system. A large fraction of the total angular momentum contributes to the formation of the circumplanetary disk. We also discuss the satellite formation from the circumplanetary disk.

Selection rules for electromagnetic transitions in triaxially deformed odd-Anuclei

The approximate selection rules for the interband and intraband electromagnetic transitions are predicted referring to two quantum numbers, which are derived from an algebraic solution for the particle-rotor model with one high-j nucleon coupled to a triaxially deformed core. It is shown that the inclusion of angular momentum dependence for moments of inertia reproduces the experimental excitation energies relative to a reference quite well both for positive and negative parity TSD bands in {sup 161,163,165,167}Lu.

Angular momentum dependence of photoionization cross section from the excited states of lithium isotopes

We present measurements of the photoionization cross sections from the $3s$, $3d$, $4s$, $4p$, and $4d$ excited states of lithium isotopes near the first ionization threshold using two dye lasers pumped by a common Nd:YAG (yttrium aluminum garnet) laser in conjunction with an atomic beam--time-of-flight mass spectrometer system. It is observed that the photoionization cross section from the $3d$ and $4d$ excited state is maximum near the ionization threshold and decreases smoothly for the excess energies above the threshold. However, for the $3s$ and $4s$ excited states, the photoionization cross section is lower at the threshold, increases to a maximum value, and then decreases monotonically for the excess energies. It is also observed that a drop off in the cross section of the $nd$ states is more hydrogenic than that of the $np$ and $ns$ excited states.

Spin dependence of critical point behavior for first and second order phase transitions in nuclei

A study of first and second order nuclear shape phase transitional behavior in yrast states of even-even nuclei in the context of the Interacting Boson Model-1 is presented. Finite boson number effects are identified using calculations with up to 150 bosons, and the role of the rotational degree of freedom of observables in first and second order quantum phase transitional nuclei is discussed. We aim to provide a first investigation of the angular momentum dependence of experimentally accessible phase transitional signatures in finite-sized quantum nuclear systems.