Properties Of Low-lying States Research Articles

Properties of low-lying states in Co65 from lifetime measurements

The low-energy structure of Co-65 was studied by means of gamma(-) and fast-timing spectroscopy at the ISOLDE/CERN facility. The known level scheme of Co-65 populated following the beta(-) decay of Fe-65 was expanded. The experimental results were compared with large-scale shell-model calculations. The measured long lifetime of the (1/2(1)(-)) level confirms its nature as a highly collective state with proton excitations across the Z = 28 gap and neutrons across the N = 40 subshell.

Nuclear structure of 76Ge from proton-neutron interacting boson model calculations

The properties of low-lying states in $^{76}$Ge, especially the characteristics of themixed-symmetry states, have been investigated within the neutron-proton interactingboson model (IBM-2). By considering the relative energy of $d$ proton boson to bedifferent from that of neutron boson, the low-lying positive parity levels and $M1$, $E2$transition strengths have been calculated. The IBM-2 calculated results are in goodagreement with the experimental data. Particularly, the mixed-symmetry states have beenreproduced quite well. The calculation and systematic analysis demonstrated that thecollective character of $^{76}$Ge lies closest to the $\textrm{SU}^{\ast}_{\pi\nu}(3)$, with some possible $\textrm{O}_{\pi\nu}(6)$ dynamic symmetry in IBM-2 viewpoint.

Description of mixed symmetry states in 96Ru using IBM-2

We have investigated the properties of low-lying states in 96Ru within the framework of the neutron-proton interacting boson model (IBM-2), with special attention paid to the characteristics of the mixed symmetry states. By considering the relative energy of d proton boson to be different from that of neutron boson, the level energies and M1, E2 transition strengths have been calculated. The IBM-2 calculation is consistent with the experimental data of 96Ru both quantitatively and qualitatively. Particularly, the strong M1 transition between the 42+ and 41+ states has been reproduced nicely. The calculated results show that the M1 transition strength of B(M1; 42+ → 41+) in 96Ru can be described successfully by the IBM-2.

The interacting quasiparticle–phonon picture and odd–even nuclei. Overview and perspectives

The role of the nucleon correlations in the ground states of even–even nuclei on the properties of low-lying states in odd–even spherical and transitional nuclei is studied. We reason about this subject using the language of the quasiparticle–phonon model which we extend to take account of the existence of quasiparticle⊗phonon configurations in the wave functions of the ground states of the even–even cores. Of paramount importance to the structure of the low-lying states happens to be the quasiparticle–phonon interaction in the ground states which we evaluated using both the standard and the extended random phase approximations. Numerical calculations for nuclei in the barium and cadmium regions are performed using pairing and quadrupole–quadrupole interaction modes which have the dominant impact on the lowest-lying states’ structure. It is found that states with same angular momentum and parity become closer in energy as compared to the predictions of models disregarding the backward amplitudes, which turns out to be in accord with the experimental data. In addition we found that the interaction between the last quasiparticle and the ground-state phonon admixtures produces configurations which contribute significantly to the magnetic dipolemoment of odd-A nuclei. It also reveals a potential for reproducing their experimental values which proves impossible if this interaction is neglected.

Study of lifetimes of low-lying levels in 53Mn

The properties of low-lying states of 53Mn were investigated via the 53Cr(p, n $\gamma$ )53Mn reaction using 4.3 MeV proton beam energy. The lifetimes of the levels at 1289.5, 1440.8, 1620.0 and 2273.8 keV excitation energies were measured using the Doppler Shift Attenuation Method (DSAM). The reduced transition probabilities B(M1) and B(E2) were extracted using the measured values of lifetimes for these levels and the mixing ratios from the literature. These values are compared with already known experimental values as well as the shell model calculations using an effective interaction.

REFINEMENT OF THE Ca-42 LEVEL SCHEME. PRELIMINARY RESULTS FROM THE FIRST AGATA DEMONSTRATOR EXPERIMENT

The Coulomb excitation experiment to study electromagnetic properties of low-lying states in 42Ca with a focus on a presumably superdeformed band was performed at the Laboratori Nazionali di Legnaro in Italy using the \gamma -ray spectrometer AGATA Demonstrator coupled to the DANTE charged particle detector array. First results are presented, including the refinement of the 42Ca level scheme.

NUCLEON PAIR APPROXIMATION OF THE SHELL MODEL: A BRIEF REVIEW

We present a brief introduction of the nucleon pair approximation (NPA) of the shell model in this paper. We review our recent calculated results which include level spectra and electromagnetic properties of low-lying states, by applying the NPA to even-even nuclei and to odd-A nuclei. We also apply this method to a few schematic systems such as single-j shell, to investigate the validity of SD-pair truncation of the shell model.

Structure of Even-Even Beryllium Isotopes Studied by AMD+GCM Method

The ground state properties and the properties of low-lying states of the even-even6Be-12Be beryllium isotopes are investigated using the extended version of the Antisymmetrized Molecular Dynamics Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground state properties of various nuclei covering light unstable nuclei. Many experimental data can be successfully reproduced by the adopted approach. Binding energies, the energies of the 2 1 + states, electromagnetic transition strengths and quadrupole moments of proton and neutron distribution are calculated.

Erratum: Properties of low-lying states in some high-nuclearity Mn, Fe, and V clusters: Exact studies of Heisenberg models [Phys. Rev. B64, 064419 (2001)

Erratum: Properties of low-lying states in some high-nuclearity Mn, Fe, and V clusters: Exact studies of Heisenberg models [Phys. Rev. B<b>64</b>, 064419 (2001)

Octupole correlations in U and Pu nuclei

We study the even-even U and Pu nuclei in the framework of the $\mathrm{spdf}$ interacting boson model. Analysis of the systematics of positive and negative parity bands, together with the $E1,$ $E2,$ and $E3$ transitions, suggests that the properties of low-lying states can be understood without the introduction of stable octupole deformation. Double octupole phonon characteristics are also identified in certain low-lying ${0}^{+}$ excited states in U and Pu.

Properties of low-lying states in some high-nuclearity Mn, Fe, and V clusters: Exact studies of Heisenberg models

Using an efficient numerical scheme that exploits spatial symmetries and spin parity, we have obtained the exact low-lying eigenstates of exchange Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}. The largest calculation involves the Mn_{12} cluster which spans a Fock space of a hundred million. Our results show that the earlier estimates of the exchange constants need to be revised for the Mn_{12} cluster to explain the level ordering of low-lying eigenstates. In the case of the Fe_8 cluster, correct level ordering can be obtained which is consistent with the exchange constants for the already known clusters with butterfly structure. In the V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the eight low-lying eigenvalues of the full Hamiltonian.

Properties of the low-lying excited states in even-even nuclei around the closed shell N=82

The properties of low-lying states in 136Ba and 144Nd are calculated within the quasiparticle phonon model. It is shown that the strong quadrupole interaction in the particle-particle channel leads to the appearance of low-lying isovector excitations. Due to this reason, there are two branches in the lowlying part of the spectrum, an isoscalar and an isovector one. Both branches show peculiar regularities of E2 and M1 transitions.

Properties of Low-Lying States in a Diffusive Quantum Dot and Fock-Space Localization

Motivated by an experiment of Sivan et al. and by subsequent theoretical work on localization in Fock space, a hierarchical model is studied numerically for a finite many-body system of fermions moving in a disordered potential and coupled by a two-body interaction. Attention is focussed on the low-lying states close to the Fermi energy. Both the spreading width and the participation number depend smoothly on excitation energy. This behavior can be fully understood in terms of the density of available 1p–0h and 2p–1h states. The system does not display localization of Anderson type. The numerical model reproduces essential features of the experiment by Sivan et al.

Properties of Low-Lying States in a Diffusive Quantum Dot and Fock-Space Localization

Motivated by an experiment by Sivan et al. (Europhys. Lett. 25, 605 (1994)) and by subsequent theoretical work on localization in Fock space, we study numerically a hierarchical model for a finite many-body system of Fermions moving in a disordered potential and coupled by a two-body interaction. We focus attention on the low-lying states close to the Fermi energy. Both the spreading width and the participation number depend smoothly on excitation energy. This behavior is in keeping with naive expectations and does not display Anderson localization. We show that the model reproduces essential features of the experiment by Sivan et al.

Properties of low-lying states in 142Ce via high resolution electron scattering.

Differential cross sections for inelastic scattering from $^{142}\mathrm{Ce}$ have been measured for excitation energies less than 3.3 MeV over a range of momentum transfer of 0.4 to 2.5 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. The data have been analyzed to extract transition charge densities. These densities are interpreted in terms of a quasiparticle-phonon approach and finite Fermi system theory to disentangle the collective and noncollective modes of excitation.

IBFFM predictions for low-lying spherical states in the shape-coexisting odd-odd nucleus98Y

Extrapolating the Interacting Boson-Model treatment from lighter neighbours to98Y we predict the properties of low-lying states of spherical nature in IBFFM. This odd-odd nucleus which presents one of the rare cases of coexisting spherical and deformed shapes is of fundamental importance for understanding nuclear phase transitions.

Fractional quantized hall effect in a model with shortranged interaction on a sphere

We consider a model forN electrons confined to the surface of a sphere in a strong radial magnetic field. The electron-electron interaction is modelled as a simple hardcore like repulsion. Numerical calculations have been carried out for up toN=6, neglecting contributions from higher Landau levels. Spectral properties of low-lying states are discussed within the quasihole-quasiparticle picture.

Structure of low-lying states inMo94

The ($p,{p}^{\ensuremath{'}}\ensuremath{\gamma}$) reaction has been used to investigate the structure of low-lying states in $^{94}\mathrm{Mo}$. Single directional correlations provided reliable branching ratios, ${J}^{\ensuremath{\pi}}$ assignments, and multipole mixing ratios from analysis of the correlations via the compound statistical theory for nuclear reactions. From these measurements the ${J}^{\ensuremath{\pi}}$ value of the 2067.1 keV level was definitely assigned as ${2}^{+}$. Lifetimes for two states in $^{94}\mathrm{Mo}$ and limits for two additional states were obtained by the Doppler-shift-attenuation method. Values of $B(M1)$ and $B(E2)$ were obtained for six transitions in $^{94}\mathrm{Mo}$. Futhermore, properties of low-lying states in $^{94}\mathrm{Mo}$ were calculated in the shell-model framework and are compared with the corresponding experimental quantities.NUCLEAR REACTIONS $^{94}\mathrm{Mo}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})$, ${E}_{p}=4.8 \mathrm{and} 5.0$ MeV, enriched targets. Measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}(\ensuremath{\vartheta})$, $\ensuremath{\Delta}{E}_{\ensuremath{\gamma}}(\ensuremath{\tau})$, deduced $^{94}\mathrm{Mo}$ levels, branching ratios, $\ensuremath{\tau}$, $\ensuremath{\delta}(\frac{E2}{M1})$, $B(E2)$, $B(M1)$; Ge(Li) detectors. Calculated $^{94}\mathrm{Mo}$ positive-parity levels, $B(E2)$, $B(M1)$, $\ensuremath{\tau}$, branching ratios.

Systematics of nuclear level properties in the lead region

This survey of the lead region is an extension of our “Survey of Nuclear Structure Systematics for A ≥ 229” (72ElSc) published previously. The mass range covered is primarily A = 190 through A = 221. The emphases are on properties of low-lying states, their shell-model configurations, and their decay modes. A comprehensive systematics of α-decay hindrance factors is presented; for β − decay, only transitions between pure single-particle states are included in the log ft systematics. For IT decays the important case of M4 transitions is presented. Magnetic dipole moments are tabulated and the additivity relation is examined. The starting point of the present survey was the Evaluated Nuclear Structure Data File (ENSDF) (see the Cumulated Index to A-Chains on page iii of this issue for references to the individual mass chains). Most changes and updates of this file, made in the course of preparing the present survey, are mentioned in the text. We refer the reader to Nuclear Data Sheets for information on high-lying states, spectroscopic factors, documentation of the data, and other topics not treated in this survey.

The structure of low-lying states of 54Mn

Abstract The structure of the low-lying states of 54 Mn has been elucidated by a high resolution study of the 55 Mn(d,t) 54 Mn reaction. A DWBA analysis of angular distributions, measured at a bombarding energy of 18 MeV, was used to extract values of the transferred orbital angular momenta and spectroscopic factors. These and other properties of low-lying states are well reproduced by a new shell- model calculation employing a realistic effective interaction. However, there is evidence of core excited states at 1071, 1388 and 1507 keV in excitation energy.