Realistic Effective Interaction Research Articles

Phase Transitions in Neutron Stars and Maximum Masses.

Using the most recent realistic effective interactions for nuclear matter with a smooth extrapolation to high densities including causality, we constrain the equation of state and calculate maximum masses of rotating neutron stars. First- and second-order phase transitions to, e.g., quark matter at high densities are included. If neutron star masses of approximately 2.3 M middle dot in circle from quasi-periodic oscillations in low-mass X-ray binaries are confirmed, a soft equation of state as well as strong phase transitions can be excluded in neutron star cores.

Level structure of120Sn:High resolution(p,t)reaction and shell model description

The $(p,t)$ reaction on ${}^{122}\mathrm{Sn}$ has been studied in a high resolution experiment at an incident proton energy of 26 MeV. The cross section angular distributions for transitions to 38 levels of ${}^{120}\mathrm{Sn}$ with an excitation energy up to $\ensuremath{\sim}3500\mathrm{keV}$ have been measured. Distorted wave Born approximation analysis of experimental angular distributions using double-folded potential for the exit channel has been done. This has made it possible to confirm previous spin and parity values and to propose new assignments for a large number of states. A shell-model study of ${}^{120}\mathrm{Sn}$ has been performed using a realistic effective interaction derived from the Paris nucleon-nucleon potential. The calculations have been carried out within the framework of the seniority scheme including states with seniority up to 4. Comparison of the calculated and experimental spectra shows a one-to-one correspondence between levels up to about 2.7 MeV excitation energy and lends support to some of the spin-parity assignments given in this work.

Proton particle-neutron hole states in132Sbwith a realistic interaction

The structure of the particle-hole nucleus ${}^{132}\mathrm{Sb}$ provides a direct source of information on the effective neutron-proton interaction in the ${}^{132}\mathrm{Sn}$ region. We have performed a shell-model calculation for this nucleus using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in very good agreement with the experimental data evidencing the reliability of our effective interaction matrix elements both with isospin $T=1$ and $T=0.$

Bonn potential and shell-model calculations for206,205,204Pb

The structure of the nuclei {sup 206,205,204}Pb is studied in terms of shell model employing a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The energy spectra, binding energies and electromagnetic properties are calculated and compared with experiment. A very good overall agreement is obtained. This evidences the reliability of our realistic effective interaction and encourages use of modern realistic potentials in shell-model calculations for heavy-mass nuclei. {copyright} {ital 1998} {ital The American Physical Society}

Study of odd-mass N = 82 isotones with realistic effective interactions

The microscopic quasiparticle-phonon model (MQPM) is used to study the energy spectra of the odd Z = 53–63, N = 82 isotones. The results are compared with experimental data, with the extreme quasiparticle-phonon limit and with the results of an unrestricted 2s1d0g 7 2 0h 11 2 shell model (SM) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the Q ̂ - box method, whereas for the MQPM the

Radiative proton capture to discrete states in 31N at 98 and 176 MeV

A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p,γ) reaction on 12C at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground state and the first three excited states of 13N. The distributions from these four states are compared with predictions from a microscopic continuum shell model calculation using a realistic finite-ranged effective interaction with tensor components. In general, reasonable agreement is obtained for reactions to states described by p shell single particle wave functions, but poor agreement is obtained for transitions described by sd shell single particle wave functions. Nevertheless we find, however, that the dominant reaction mechanism is a direct capture process. We also compare the (p,γ) data with existing data on the exclusive (p,π) reaction at 185 MeV revealing notable differences between the two reactions.

Structure of neutron-rich nuclei around 132Sn

Recent studies have provided new experimental information on neutron-rich nuclei around doubly magic {sup 132}Sn. We have performed shell-model calculations for the two- and three-proton N=82 isotones {sup 134}Te and {sup 135}I using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in remarkably good agreement with the experimental data evidencing the reliability of our realistic effective interaction. {copyright} {ital 1997} {ital The American Physical Society}

Elastic scattering of 9Li from protons at 60A MeV

A microscopic single-scattering model study of elastic scattering of ${}^{9}$Li from protons at 60 MeV/nucleon is reported. Results with two realistic effective nucleon-nucleon interactions, one adopted from the work of Mahaux and collaborators and another from the work of von Geramb and collaborators, bracket the $\ensuremath{\sigma}(\ensuremath{\theta})$ data when a simple Gaussian ground state density with rms radius 2.32 fm is used.

Extended shell model calculation for even N = 82 isotones with a realistic effective interaction

The shell model within the 2s1d0g 7 2 0h 11 2 shell is applied to calculate nuclear structure properties of the even Z = 52−62, N = 82 isotones. The results are compared with experimental data and with the results of a quasiparticle random-phase approximation (QRPA) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the Q -box method whereas for the QRPA the effective interaction is defined by the G-matrix.

Generalized seniority scheme in light Sn isotopes

In search of a possible truncation scheme for shell model calculations, the yrast generalized seniority states are compared with the corresponding shell model states for the case of the Sn isotopes ${}^{104\ensuremath{-}112}$Sn. For most of the cases the energies agree within a few hundred keV. For the ${0}^{+}$${(2}^{+})$ states the overlaps decrease from 97% (93%) in ${}^{104}$Sn to 91% (78%) in ${}^{112}$Sn when the coefficients of the pairs in the $S$ and $D$ boson operators are allowed to vary with the number of particles. For constant pairing coefficients throughout the entire isotope range, the overlaps are considerably smaller. It is concluded, with the realistic effective interaction applied here, that a truncation scheme based on seniority zero and two states is inadequate when the number of valence particles gets large and that configurations of higher seniority should be included.

Ambiguities in the elastic scattering potentials for 350 MeV7Li ions on12C and28Si

The differential cross sections from the scattering of 350 MeV ${}^{7}$Li ions from ${}^{12}$C and from ${}^{28}$Si have been analyzed by both a global and a numerical inverse scattering theory. Statistically significant fits to both high quality data sets have been found from which the associated effective local interaction potentials between the colliding ions have been deduced. The interactions obtained by the different approaches are radically different. A priori physical information about the nature of realistic effective interactions is required to ascertain which, if any, is the most reasonable one for use in analyses of other reaction data from these systems.

Nuclear structure calculations with realistic effective interactions

In this paper, we present some results of realistic shell-model calculations for the Sn isotopes and the N=82 isotones. As regards the former nuclei, we focus attention on the light even isotopes, 102,104,106Sn. The calculations are performed by making use of two realistic effective interactions derived from the Bonn A and Paris nucleon-nucleon potentials, respectively. From the comparison of the calculated spectra with the experimental ones it turns out that the best agreement is obtained with the weaker tensor force potential (Bonn A). For the N=82 isotones, we study the behavior of the energy of some low-lying states in the nuclei with A ranging from 134 to 148. In this case, only the results obtained by using the Bonn potential are reported. The agreement between theory and experiment is quite satisfactory for all of the considered nuclei. This evidences the merit of modern realistic interactions in nuclear structure calculations.

Realistic shell-model calculations for neutron deficient Sn isotopes.

We have performed shell-model calculations for $^{102,103,104,105}\mathrm{Sn}$ using two realistic effective interactions derived from the Bonn A and Paris nucleon-nucleon potentials, respectively. From the comparison of the calculated spectra of $^{104}\mathrm{Sn}$ and $^{105}\mathrm{Sn}$ with the experimental ones it turns out that the best agreement is obtained with the weaker tensor force potential (Bonn A). This agreement appears to be significantly better than for other nuclear regions, such as the sd shell, and thus encourages use of modern realistic potentials in shell-model calculations for medium- and heavy-mass nuclei. In addition, it supports confidence in our predictions of the spectra of the hitherto unknown isotopes $^{102}\mathrm{Sn}$ and $^{103}\mathrm{Sn}$. \textcopyright{} 1996 The American Physical Society.

Projected quasi-particle calculations of 119Sn, 121Sn, and 123Sn using realistic interactions

We have performed quasi-particle calculations for the tin isotopes 119Sn, 121Sn and 123Sn, using realistic effective interactions derived from the Paris and Bonn-A NN potentials. A number-projected one- and three-quasi-particle formalism in the (g72, d52, d32, s12, h112) model space is employed. We have used a folded-diagram method to derive the corresponding model-space effective interaction, starting from the G-matrix elements derived from the above NN potentials. The G-matrix Pauli-exclusion operator Q2, specified by the shell-model orbitals (n1, n2, n3) = (11, 21, 36), has been treated accurately. An almost pure (h112)3 three-quasiparticle structure for the high spin states from J = 172− to 272− of the above nuclei has been observed. With practically no parameter adjustment, our calculated energies are in very good agreement with available experimental data.

Realistic effective interactions for halo nuclei

We study halo nuclei using a two-frequency shell-model approach employing wave functions of two different oscillator constants $\hbar\omega_{in}$ and $\hbar\omega_{out}$, the former for the inner orbits and the latter for the halo (outer) orbits. An initial application has been made for the halo nuclei $^6$He and $^6$Li, with $0s_{1/2}$ taken as the inner and ( $0p_{3/2}$, $0p_{1/2}$) as the halo orbits. Starting from the Paris NN interaction, we have derived a G-matrix folded-diagram effective interaction for this two-frequency model space, using an essentially exact treatment for the Pauli exclusion operator for the G-matrix. While keeping $\hbar\omega_{in}$ fixed, we have performed calculations with different choices for $\hbar\omega_{out}$, treating it as a variation parameter. For $\hbar\omega_{in}=19.7 MeV$ and $\hbar\omega_{out}=8.2 MeV$, our calculated valence energies for $^6$He and $^6$Li are -2.77 and -3.55 Mev, respectively, both in good agreement with experiments. The importance of certain three-body-force diagrams is discussed.

Radiative proton capture to discrete states in 12C at 98 and 176 MeV

A high-resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p, γ) reaction on 11B at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground and first three excited states of 12C. The distributions from the three lowest lying states are compared with predictions from a microscopic continuum shell-model calculation using a realistic finite-ranged effective interaction with tensor components. Exchange current effects are examined in detail as both Δ(1232) isobar and pion exchange currents are rigorously included. In general, a good theoretical description of the data is obtained. The predominant reaction mechanism involves photon emission by the nucleonic one-body current.

Statistical properties of antisymmetrized molecular dynamics for non-nucleon-emission and nucleon-emission processes.

Statistical properties of antisymmetrized molecular dynamics (AMD) are classical in the case of nucleon-emission processes, while they are quantum mechanical for the processes without nucleon emission. In order to understand this situation, we first clarify that there coexist mutually opposite two statistics in the AMD framework: One is the classical statistics of the motion of wave packet centroids and the other is the quantum statistics of the motion of wave packets which is described by the AMD wave function. We prove the classical statistics of wave packet centroids by using the framework of the microcanonical ensemble of the nuclear system with a realistic effective two-nucleon interaction. We show that the relation between the classical statistics of wave packet centroids and the quantum statistics of wave packets can be obtained by taking into account the effects of the wave packet spread. This relation clarifies how the quantum statistics of wave packets emerges from the classical statistics of wave packet centroids. It is emphasized that the temperature of the classical statistics of wave packet centroids is different from the temperature of the quantum statistics of wave packets. We then explain that the statistical properties of AMD for nucleon-emission processes are classical becausemore » nucleon-emission processes in AMD are described by the motion of wave packet centroids. We further show that when we improve the description of the nucleon-emission process so as to take into account the momentum fluctuation due to the wave packet spread, the AMD statistical properties for nucleon-emission processes change drastically into quantum statistics. Our study of nucleon-emission processes can be conversely regarded as giving another kind of proof of the fact that the statistics of wave packets is quantum mechanical while that of wave packet centroids is classical. {copyright} {ital 1996 The American Physical Society.}« less

Realistic scenario for the quasielastic scattering of 11Li, 11C+ 12C at [formula omitted

The elastic 11Li, 11C+ 12C scattering at E A ∼- 60 MeV has been studied using a semimicroscopic version of the optical model. The real optical potential was calculated within the double-folding model using a realistic nucleon-nucleon effective interaction and a more accurate treatment of the knock-on exchange. A Hartree-Fock density was taken for 11Li, while the shell model was used for 11,12C. The imaginary potential was taken in standard Woods-Saxon form. The dynamic polarization potential due to the breakup effect, based on the results of realistic four-body calculations of the 11Li+ 12C scattering, has been added to both the real and imaginary potentials for 11Li. From different assumptions about the absorptive strength at the surface region, we found a set of parameters which give a reasonable description of the quasielastic 11Li, 11C+ 12C scattering data at E A ∼- 60 MeV as well as reproducing the observed trend for the total reaction cross section at higher energies.

Large shell model calculations with realistic effective interaction

In this work we discuss methods to calculate shell model effective interaction, starting from the basic nucleon-nucleon interaction. The result is applied in large shell model calculations using the Lanczos iterative method with m-scheme basic states. Perspectives for such large-scale shell model calculations with realistic effective interactions in heavy nuclei are discussed. Results are shown for the Sn isotopes.

Delta excitations in compressed finite nuclei.

We treat $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, and $^{56}\mathrm{Ni}$ as systems of baryons which can exist in either the ground (nucleon) state or first excited (delta) state and follow their behavior under static comrpession using constrained spherical Hartree-Fock approximation (SHF). We use realistic effective nucleon-nucleon interactions with meson-exchange-based nucleon-delta transition potentials and delta-delta interactions and we make phenomenological adjustments to obtain SHF equilibrium properties in agreement with experiment. We then show how physical properties are affected by delta excitation under compression. We find that a significant fraction of the increase in energy of these nuclei under compression is stored in the form of \ensuremath{\Delta}-mass creation. This, in turn, may have implications for an enhanced role for nuclear compression in subthreshold pion production in nucleus-nucleus collisions. In addition, including the deltas leads to a lower compressibility of each of these nuclei.