Showing papers in "International Journal of Modern Physics E-nuclear Physics in 2004"
TL;DR: In this paper, the authors present a unified derivation of most of the phenomenological approaches being used to extract the resonance parameters from the data, and the analyses of π and η production data and the resulting transition form factors for the Δ(1232)P33, N(1535)S11, N 1440)P11, and N 1520)D13 resonances are discussed in detail.
Abstract: Recent experimental and theoretical advances in investigating electromagnetic meson production reactions in the nucleon resonance region are reviewed. We give a description of current experimental facilities with electron and photon beams and present a unified derivation of most of the phenomenological approaches being used to extract the resonance parameters from the data. The analyses of π and η production data and the resulting transition form factors for the Δ(1232)P33, N(1535)S11, N(1440)P11, and N(1520)D13 resonances are discussed in detail. The status of our understanding of the reactions with production of two pions, kaons, and vector mesons is also reviewed.
135 citations
TL;DR: In this paper, the authors present the results of numeric calculations of spectral distributions of the spontaneous radiation emitted in the crystalline undulator and discuss the possibility to create the stimulated emission in such a system in analogy with the free electron laser.
Abstract: The electromagnetic radiation generated by ultra-relativistic positrons channeling in a crystalline undulator is discussed. The crystalline undulator is a crystal whose planes are bent periodically with the amplitude much larger than the interplanar spacing. Various conditions and criteria to be fulfilled for the crystalline undulator operation are established. Different methods of crystal bending are described. We present the results of numeric calculations of spectral distributions of the spontaneous radiation emitted in the crystalline undulator and discuss the possibility to create the stimulated emission in such a system in analogy with the free electron laser. A careful literature survey covering the formulation of all essential ideas in this field is given. Our investigation shows that the proposed mechanism provides an efficient source for high energy photons, which is worth studying experimentally.
69 citations
TL;DR: In this article, the Klein-Gordon equation with a Coulomb plus scalar potential in D dimensions is analyzed and the dependence of the energy E(n,l,D) on the dimension D is analyzed in some detail.
Abstract: The solutions of the Klein–Gordon equation with a Coulomb plus scalar potential in D dimensions are exactly obtained. The energy E(n,l,D) is analytically presented and the dependence of the energy E(n,l,D) on the dimension D is analyzed in some detail. The positive energy E(n,0,D) first decreases and then increases with increasing dimension D. The positive energy E(n,l D)(l≠0) increases with increasing dimension D. The dependences of the negative energies E(n,0,D) and E(n,l,D)(l≠0) on the dimension D are opposite to those of the corresponding positive energies E(n,0,D) and E(n,l,D)(l≠0). It is found that the energy E(n,0,D) is symmetric with respect to D=2 for D∈(0,4). It is also found that the energy E(n,l,D)(l≠0) is almost independent of the angular momentum quantum number l for large D and is completely independent of the angular momentum quantum number l if the Coulomb potential is equal to the scalar one. The energy E(n,l D) is almost overlapping for large D.
66 citations
TL;DR: In this article, the nuclear periphery was studied by using antiprotons and two experimental methods were applied: analysis of the antiproton annihilation residues one mass unit lighter than the target mass by nuclear spectroscopy and the measurement of strong interaction effects on antipprotonic level widths and shifts.
Abstract: The nuclear periphery was studied by using antiprotons. Two experimental methods were applied: analysis of the antiproton annihilation residues one mass unit lighter than the target mass by nuclear spectroscopy and the measurement of strong interaction effects on antiprotonic level widths and shifts. 26 isotopes from a wide range of mass numbers (40
65 citations
TL;DR: In this paper, the relativistic mean-field plus BCS (RMF+BCS) approach was used for the calculation of pairing energy for drip-line neutron-rich nuclei, where the single particle continuum corresponding to the RMF was replaced by a set of discrete positive energy states.
Abstract: Recently, it has been demonstrated, considering Ni and Ca isotopes as prototypes, that the relativistic mean-field plus BCS (RMF+BCS) approach wherein the single particle continuum corresponding to the RMF is replaced by a set of discrete positive energy states for the calculation of pairing energy provides a good approximation to the full relativistic Hartree–Bogoliubov (RHB) description of the ground state properties of drip-line neutron rich nuclei. The applicability of the RMF+BCS approach even for the drip-line nuclei is essentially due to the fact that the main contribution to the pairing correlations for the neutron rich nuclei is provided by the low-lying resonant states, in addition to the contributions coming from the states close to the Fermi surface. In order to show the general validity of this approach we present the results of our detailed calculations for the ground state properties of the chains of isotopes of O, Ca, Ni, Zr, Sn and Pb nuclei. The TMA force parameter set has been used for the effective mean-field Lagrangian with nonlinear terms for the sigma and omega mesons. Further, to check the validity of our treatment for different mean-field descriptions, calculations have also been carried out for the NL-SH force parametrization usually employed for the description of drip-line nuclei. Comprehensive results for the two neutron separation energy, rms radii, single particle pairing gaps and pairing energies etc. are presented. In particular, the Ca isotopes are found to exhibit distinct features near the neutron drip line whereby it is found that further addition of neutrons causes a rapid increase in the neutron rms radius with almost no increase in the binding energy, indicating the occurrence of halos. This is mainly caused by the pairing correlations and results in the existence of bound states of extremely neutron rich exotic nuclei. Similar characteristics, though less pronounced, are also exhibited by neutron rich Zr isotopes. A comparison of these results with the available experimental data and with the recent continuum relativistic Hartree–Bogoliubov (RCHB) calculations amply demonstrates the validity and usefulness of this fast RMF+BCS approach for the description of nuclei including those near the drip-lines.
41 citations
TL;DR: In this article, an explanation of the anomalous positron production via the complex nature of the symplictic vacuum is attempted, where it is conjectured that a host of highly unstable exotic particles and weakly interacting neutral bosons may be produced under certain extreme conditions, for instance a very strong electromagnetic field.
Abstract: In the present paper the phenomenon of anomalous positron production is reconsidered. An explanation of the phenomenon via the complex nature of the symplictic vacuum is attempted. This is a vacuum, akin to that of Dirac's but with an additional transfinite correction and fractal fine structure. It is conjectured that not only one, but a host of highly unstable exotic particles and weakly interacting neutral bosons may be produced under certain extreme conditions, for instance a very strong electromagnetic field. It is further shown that these particles are intimately linked to the production of mini black holes via the instanton method within the VAK of vacuum fluctuation. One of the principle conclusions in the present work is that while a symmetry breaking is accompanied by the appearance of a corresponding (new) particle, a symmetry breaking of the "average" or complex "quasi" symmetry of the VAK will be logically associated with a host of (new) "quasi" particles. This may be the explanation for the experimental observations related to the said anomalous positron production.
32 citations
TL;DR: In this paper, a new theoretical framework for modeling the fusion process of LJ clusters is presented, and all known global minima structures of the LJ-clusters can be found.
Abstract: We present a new theoretical framework for modeling the fusion process of Lennard–Jones (LJ) clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster size of 150 atoms. We demonstrate that in this way all known global minima structures of the LJ-clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence for the clusters of noble gas atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence of the second derivative of the binding energy per atom on cluster size calculated for the chain of the LJ-clusters based on the icosahedral symmetry with the peaks in the abundance mass spectra experimentally measured for the clusters of noble gas atoms. Our method serves as an efficient alternative to the global optimization techniques based on the Monte-Carlo simulations and it can be applied for the solutions of a broad variety of problems in which atomic cluster structure is important.
26 citations
TL;DR: In this paper, the charge form factors corresponding to proton density distributions in exotic nuclei, such as 6,8He, 11Li, 17,19B and 14Be, are calculated and compared.
Abstract: Charge form factors corresponding to proton density distributions in exotic nuclei, such as 6,8He, 11Li, 17,19B and 14Be are calculated and compared. The results can be used as tests of various theoretical models for the exotic nuclei structure in possible future experiments using a colliding electron-exotic nucleus storage ring. The result of such a comparison would show the effect of the neutron halo or skin on the proton distributions in exotic nuclei.
22 citations
TL;DR: In this article, a method of calculating giant resonance strength functions using Time-Dependent Hartree-Fock techniques is described, and an application to isoscalar giant monopole resonances in spherical nuclei is made, thus allowing a comparison between independent 1-, 2-and 3-dimensional computer codes.
Abstract: A method of calculating giant resonance strength functions using Time-Dependent Hartree-Fock techniques is described. An application to isoscalar giant monopole resonances in spherical nuclei is made, thus allowing a comparison between independent 1-, 2- and 3-Dimensional computer codes.
21 citations
TL;DR: The recently revised liquid drop model (PRC 67(2003) 044316) containing the curvature term reproduces the masses of 2766 experimentally known isotopes having Z ≥ 8 and N ≥ 8 with the r.m.s. deviation equal to 0.698 MeV when the microscopic corrections of Moeller et al. as mentioned in this paper is used.
Abstract: The recently revised liquid drop model (PRC 67(2003) 044316) containing the curvature term reproduces the masses of 2766 experimentally known isotopes having Z≥8 and N≥8 with the r.m.s. deviation equal to 0.698 MeV when the microscopic corrections of Moeller et al. is used. The influence of the congruence energy as well as the compression term on the barrier heights is discussed within this new macroscopic model. The r.m.s. deviation of the fission barrier heights of 40 isotopes with Z≥34 is 1.73 MeV only when deformation-dependent congruence energy is included. The effect of the compression term in the liquid drop energy has rather weak influence on the barrier heights.
20 citations
TL;DR: This work presents a concise account of the development of the first genuine Local Density Approximation to the Energy Density Functional for fermionic systems with superfluid correlations, with a particular emphasis to nuclear systems.
Abstract: We present a concise account of our development of the first genuine Local Density Approximation (LDA) to the Energy Density Functional (EDF) for fermionic systems with superfluid correlations, with a particular emphasis to nuclear systems.
TL;DR: In this paper, the authors used the 82Se+192Os deep-inelastic reaction to populate neutron rich nuclei using a beam-like beam-forming beamforming method.
Abstract: Neutron rich nuclei have been populated using the 82Se+192Os deep-inelastic reaction. New experimental results on 188W, 188,190Os target-like nuclei, as well as 74,76,78Ge beam-like nuclei are presented.
TL;DR: In this article, the Dirac equation in D+1 dimensional space-time is investigated and the radial equations of this quantum system are obtained and solved exactly by the confluent hypergeometric equation approach.
Abstract: The Dirac equation is investigated in D+1 dimensional space-time. The radial equations of this quantum system are obtained and solved exactly by the confluent hypergeometric equation approach. The energy levels E(n,l,D) are analytically presented. For the continuous dimension D as proposed by Nieto, the dependences of the energy difference ΔE(n,l,D) for D and D-1 on the dimension D are demonstrated as three different kinds of change rules. The dependences of the energy E(n,l,D) on the dimension D are also discussed. It is found that the energies E(n,l,D) (l≠0) are almost independent of the quantum number l for a large D, while E(n,0,D) first decreases and then increases with the increasing dimension D. The dependences of the energies E(n,l,ξ) on the potential strength ξ are also studied for the given dimension D=3. We find that the energies E(n,l,ξ) decrease with ξ≤l+1.
TL;DR: In this article, a generalized parameterization of the Skyrme effective force is discussed for infinite symmetric and asymmetric nuclear matter, and it is shown that an enlarged density dependence based on two terms allows to choose independently the incompressibility and the isoscalar effective mass.
Abstract: A generalized parameterization of the Skyrme effective force is discussed. Preliminary results are presented for infinite symmetric and asymmetric nuclear matter. In particular, it is shown that an enlarged density dependence based on two terms allows to choose independently the incompressibility and the isoscalar effective mass.
TL;DR: In this paper, the results on the population of specific structures of large deformation in light N = Z nuclei were presented. But the results were obtained with the Binary Reaction Spectrometer (BRS) installed at the VIVITRON.
Abstract: Nuclear alpha-clustering has been the subject of intense study since the advent of heavy-ion accelerators. Looking back for more than 40 years we are able today to see the connection between quasimolecular resonances in heavy-ion collisions and extremely deformed states in light nuclei. For example superdeformed bands have been recently discovered in light N=Z nuclei such as 36Ar, 40Ca, 48Cr, and 56Ni by γ-ray spectroscopy. The search for strongly deformed shapes in N=Z nuclei is also the domain of charged-particle spectroscopy, and a number of these nuclei have been studied with the charged particle multidetector array ICARE at the VIVITRON. Recently the search for γ-decays in 24Mg has been undertaken in a range of excitation energies where previously nuclear molecular resonances were found in 12C+12C collisions. The breakup reaction 24Mg+12C has been investigated at an energy which corresponds to a 12C+12C resonance. Very exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON. Results on the population of specific structures of large deformation will be presented.
TL;DR: In this paper, the relation between strong isospin I and weak isosospin i is discussed and an equation between the third components I3 and i3 is given, which indicates that the strong and weak symmetries are SU(2) subgroups of a new SU(3) symmetry underlying the structure of leptons and quarks.
Abstract: The relation between strong isospin I and weak isospin i is discussed. In particular an equation between the third components I3 and i3 is given. This relation indicates that the strong isospin and weak isospin symmetries are both SU(2) subgroups of a new SU(3) symmetry underlying the structure of leptons and quarks.
TL;DR: In this paper, the authors analyzed shell structures in nuclear mean field potentials using semiclassical periodic-orbit theory and found significant roles of periodic orbit bifurcations for strong deformed shell effects.
Abstract: Shell structures in nuclear mean field potentials are analyzed using semiclassical periodic-orbit theory. rα-type potential model is taken as an approximation of Woods-Saxon model, and spin-orbit coupling is also taken into account. Using this model, we examine shell structure as functions of deformation, nuclear size (diffuseness), and spin-orbit coupling strength. Significant roles of periodic orbit bifurcations for strong deformed shell effects are clarified. Special attentions will be paid to bifurcations of the 'bridge orbits', which emerge from symmetric orbits and then submerge in other symmetric orbits by varying a potential parameter.
TL;DR: In this article, the lifetime of the h11/2 decoupled band in 131La and supposed chiral bands in odd-odd 132La have been measured using the Doppler Shift Atenuation method.
Abstract: Lifetimes of the h11/2 decoupled band in 131La and supposed chiral bands in odd-odd 132La have been measured using the Doppler Shift Atenuation method. The properties of all bands have been calculated in terms of the Core Quasi Particle Coupling and Core Particle Hole Coupling models by using in both cases the same phenomenological core of 130Ba. A new band in 132La has been found.
TL;DR: In this paper, the authors summarize recent developments of the semiclassical description of shell effects in finite fermion systems with explicit inclusion of spin degrees of freedom, in particluar in the presence of spin-orbit interactions.
Abstract: We summarize recent developments of the semiclassical description of shell effects in finite fermion systems with explicit inclusion of spin degrees of freedom, in particluar in the presence of spin-orbit interactions. We present a new approach that makes use of spin coherent states and a correspondingly enlarged classical phase space. Taking suitable limits, we can recover some of the earlier approaches. Applications to some model systems are presented.
TL;DR: In this article, the predictions obtained in the domain of superheavy nuclei from self-consistent microscopic calculations employing the Gogny force are summarized, and the results concerning shell gaps, fission barriers and stability against alpha-decay are recalled.
Abstract: This contribution summarizes the predictions obtained in the domain of superheavy nuclei from self-consistent microscopic calculations employing the Gogny force. Results concerning shell gaps, fission barriers and stability against alpha-decay are recalled. Recent work involving α-decay chains in odd nuclides is also presented and discussed.
TL;DR: In this paper, the fusion cross sections are given by the product of three factors: the cross section to overcome the Coulomb barrier, the probability for the resulting system to reach the compound nucleus configuration by diffusion, and the probability of surviving fission.
Abstract: The fusion cross sections are considered to be given by the product of three factors: the cross section to overcome the Coulomb barrier, the probability for the resulting system to reach the compound nucleus configuration by diffusion, and the probability for the compound nucleus to survive fission. The first and third factors are treated by more or less conventional equations, and the second by Brownian diffusion in one dimension. Adjusting one free parameter in the theory one can reproduce the twelve measured cross sections to within a factor of two.
TL;DR: In this paper, the authors used the symmetry-unrestricted, cranked Skyrme-Hartree-Fock (SHF) calculations on the superdeformed (SD) rotational bands in (1) the 40Ca region along the N=Z line, and (2) neutron-rich Sulfur isotopes up to the neutron-drip line.
Abstract: On the basis of the symmetry-unrestricted, cranked Skyrme-Hartree-Fock (SHF) calculations, we discuss superdeformed (SD) rotational bands in (1) the 40Ca region along the N=Z line, and (2) neutron-rich Sulfur isotopes up to the neutron-drip line. The calculation was carried out with the use of the three-dimensional (3D) coordinate-mesh representation without imposing any symmetry restriction. Stability of the SD bands against exotic deformations breaking both reflection and axial symmetries were carefully examined. The analysis indicates possible appearance of negative-parity rotational bands associated with octupole shape vibrational excitations built on the SD yrast band. We then present results of selfconsistent RPA calculation for such a new type of collective vibrational modes. The selfconsistent RPA calculations based on the SD local minima obtained by the SHF calculation were carried out by means of the mixed representation on the 3D Cartesian mesh in a box.
TL;DR: The inner crust of a neutron star consists of nuclei immersed in a superfluid neutron liquid, and as these nuclei move through the fermionic medium they bring it into motion as well as mentioned in this paper.
Abstract: The inner crust of a neutron star consists of nuclei immersed in a superfluid neutron liquid. As these nuclei move through the fermionic medium they bring it into motion as well. As a result their mass is strongly renormalized and the spectrum of the ion lattice vibrations is significantly affected. Consequently we predict that the specific heat and the lattice thermal energy of the Coulomb crystal at these densities are noticeably modified.
TL;DR: In this paper, the authors performed constrained HFB calculations with the Gogny force to investigate the bimodal fission of a single-particle orbitals in both fission modes, showing that the cores of the fragments are well separated far before the scission point.
Abstract: Constrained HFB calculations with the Gogny force are performed in order to investigate the bimodal fission of 258Fm. The single-particle orbitals are analyzed in both fission modes. Density distributions of single nucleons show that the cores of the fragments are well separated far before the scission point.
TL;DR: In this article, the authors investigated the occurrence of the non-thermal phase transition in the target fragmentation of 28Si-AgBr interactions at 14.5 AGeV in azimuthal angle space using the method of factorial moment.
Abstract: This paper reports an investigation on the occurrence of the non-thermal phase transition in the target fragmentation of 28Si–AgBr interactions at 14.5 AGeV in azimuthal angle space using the method of factorial moment. Clear evidence of the non-thermal phase transition is obtained.
TL;DR: In this paper, the authors presented the new experimental results obtained in some neutron-rich odd-Z nuclei from 43Tc to 49In, where all the band-head configurations have been identified from the behaviour of the collective bands built on them.
Abstract: Using the Euroball array, we have recently performed several experiments devoted to the study of high-spin states of nuclei with A~80–130, produced from fission following various fusion reactions. High-spin level schemes of many neutron-rich nuclei have been extended or newly established. We present here the new experimental results obtained in some neutron-rich odd-Z nuclei from 43Tc to 49In. All the band-head configurations have been identified from the behaviour of the collective bands built on them. Therefore the single-proton states, located around the Fermi levels for Z=43 to 49, can be discussed as a function of the neutron number (and the deformation). In all these isotopic series, three-quasiparticle states have been measured above 2 MeV excitation energy. The case of 49In nuclei is discussed in the framework of shell-model calculations. Futhermore the individual identification of each fragment by means of its emitted γ transitions allows us to have a new insight into the mechanism of fission induced by heavy ions. Preliminary results of the total number of emitted neutrons are discussed as a function of the N/Z ratios of the fragments.
TL;DR: In this article, a phenomenological method of analysis for heavy-ion elastic scattering data at intermediate energies is proposed, which is based on the Coulomb modified Glauber model and the optical limit approximation.
Abstract: Working within the framework of the Coulomb modified Glauber model and the optical limit approximation, we propose a phenomenological method of analysis for heavy-ion elastic scattering data at intermediate energies. Instead of using the commonly employed Gaussian approximation for the input NN amplitude that is deficient in some respects at low intermediate energies, we evaluate it in terms of a three parameter phenomenological NN phase shift function. The application of the method to some 12C-nucleus and 16O-nucleus systems shows that a very good description of the elastic scattering data at several energies can be obtained in this way. In particular, the 12C–12C elastic scattering data at 200 MeV/nucleon is very well reproduced. We also calculate the effective NN potential using the phenomenological NN phase shift function by the method of inversion. The calculated potential shows the expected behavior and is found to vary smoothly with energy.
TL;DR: In this paper, the geometry dependent hybrid (GDH) model has been compared with the stacked foil activation technique and γ-ray spectroscopy method to measure the excitation functions for the reactions (α, 2n), (ααn), α,αn, α, α2n, β,α2n), β, α3n, and β, 2pn) up to 50 MeV α-particle energy.
Abstract: Excitation functions for the reactions (α,2n), (α,αn), (α,α2n), (α,α3n) and (α,2pn) have been measured using 57Co as a target up to 50 MeV α-particle energy. The stacked foil activation technique and γ-ray spectroscopy method has been employed. Measured excitation functions are compared with the geometry dependent hybrid (GDH) model. A comparison shows that the pure equilibrium (EQ) compound reaction mechanism is incapable of reproducing the experimental data while the pre-equilibrium (PE) reaction mechanism along with equilibrium (EQ) decay, where it is considered that pre-equilibrium emission of particles take place prior to the establishment of the thermodynamical equilibrium of the system, is able to reproduce the experimental data. The GDH model code ALICE-91 has been used for theoretical calculations. A value of initial exciton number n0=4 with configuration (2 neutron + 2 proton + 0 hole) has been found to give the satisfactory reproduction of experimental excitation functions.
TL;DR: In this article, the Strutinsky shell corrections from the selfconsistent energies obtained within the Relativistic Mean Field Theory (RMFT) were used to obtain estimates for the macroscopic part of the binding energies of 142 spherical even-even nuclei.
Abstract: Subtracting the Strutinsky shell corrections from the selfconsistent energies obtained within the Relativistic Mean Field Theory (RMFT) we have got estimates for the macroscopic part of the binding energies of 142 spherical even-even nuclei. By minimizing their root-mean-square deviations from the values obtained with the Lublin-Srasbourg Drop (LSD) model with respect to the nine RMFT parameters we have found the optimal set (NL4). The new parameters reproduce also the radii of these nuclei with an accuracy comparable to that obtained with the NL1 and NL3 sets.
TL;DR: In this article, the variation of nuclear shell effects with nucleon numbers was evaluated using the modified Bethe-Weizsacker mass formula (BWM) and the measured atomic masses.
Abstract: The variation of nuclear shell effects with nucleon numbers is evaluated using the modified Bethe–Weizsacker mass formula (BWM) and the measured atomic masses. The shell effects at magic neutron numbers N=8, 20, 28, 50, 82 and 126 and magic proton numbers Z=8, 20, 28, 50 and 82 are found to vary rapidly approaching the drip-lines. The shell effect due to one magic number increases on approaching another magic number. Thus, shell effects are not always negligible near the drip-lines.