Search results for "ISOSCALAR"

Spurious finite-size instabilities in nuclear energy density functionals: Spin channel

2015

Background: It has been recently shown that some Skyrme functionals can lead to nonconverging results in the calculation of some properties of atomic nuclei. A previous study has pointed out a possible link between these convergence problems and the appearance of finite-size instabilities in symmetric nuclear matter (SNM) around saturation density. Purpose: We show that the finite-size instabilities not only affect the ground-state properties of atomic nuclei, but they can also influence the calculations of vibrational excited states in finite nuclei. Method: We perform systematic fully-self consistent random phase approximation (RPA) calculations in spherical doubly magic nuclei. We employ…

Isospin Character of Low-Lying Pygmy Dipole States inPb208via Inelastic Scattering ofO17Ions

2014

The properties of pygmy dipole states in Pb-208 were investigated using the Pb-208(O-17, O-17'gamma) reaction at 340 MeV and measuring the gamma decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted gamma rays and of the scattered particles were measured. The results are compared with (gamma, gamma') and (p, p') data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the 2(+) and 3(-) states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first t…

Identification of Excited States in theTz=1NucleusXe110: Evidence for Enhanced Collectivity near theN=Z=50Double Shell Closure

2007

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient (N=Z+2) nucleus {sup 110}Xe, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited 2{sup +} and 4{sup +} level energies as a function of the decreasing neutron number as the N=50 major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar n-p interactions becoming increasingly important close to the N=Z line.

2018

We have performed the most comprehensive resonance-model fit of π-π-π+ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π-+p→π-π-π++precoil with a 190  GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5<m3π<2.5  GeV/c2, and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1<t′<1.0  (GeV/c)2, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with JPC=0-+, 1++, 2++, 2-+, 4++, and spin-exotic 1-+ quantum numbers. T…

Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru88

2020

The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88 44Ru44 has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88Ru were populated via the 54Fe(36Ar; 2n )88Ru fusion-evaporation reaction at the Grand Acc�el�erateur National d'Ions Lourds (GANIL) accelerator complex. The observed -ray cascade is assigned to 88Ru using clean prompt - -2-neutron coincidences in anti-coincidence with the detection of charged particles, con�rming and extending the previously assigned sequence of low-lyin…

Nonquenched Isoscalar Spin-M1Excitations insd-Shell Nuclei

2015

Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295  MeV on (24)Mg, (28)Si, (32)S, and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16  MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transi…

E1 andE2/E0 form factors and strength distributions fromSi28(e,e’p) andSi28(e,e’α) coincidence scattering

1986

A model-independent multipole analysis of $^{28}\mathrm{Si}$(e,e'p) and $^{28}\mathrm{Si}$(e,e'\ensuremath{\alpha}) coincidence data, taken at three momentum transfers 0.39lql0.68 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$, yields both E1 and E2/E0 form factors and the respective multipole strength distributions in the giant-resonance region of $^{28}\mathrm{Si}$ (${E}_{x}$=14--22 MeV). While the deduced E1 strength agrees well with previous results, the total extracted E2/E0 strength is about twice the value found with isoscalar projectiles indicating the presence of large isovector E2/E0 contributions in the region of the isoscalar E2/E0 giant resonances.

High temperature giant dipole and isoscalar resonances

1990

We present a systematic study of the Giant Dipole Resonance (GDR) at high temperatures (T≧4 MeV) in the framework of a semiclassical approximation that uses them1 andm3 RPA sum rules to estimate the GDR mean energy. We focus on the evolution withT of the collective nature of the GDR and of theL=0, 2, 3 and 4 isoscalar resonances. We find that the GDR remains particularly collective at highT, suggesting that it might be possible to observe it experimentally even at temperatures close to the maximum one a nucleus can sustain.

Self-consistent symmetries in the proton-neutron Hartree-Fock-Bogoliubov approach

2009

Symmetry properties of densities and mean fields appearing in the nuclear Density Functional Theory with pairing are studied. We consider energy functionals that depend only on local densities and their derivatives. The most important self-consistent symmetries are discussed: spherical, axial, space-inversion, and mirror symmetries. In each case, the consequences of breaking or conserving the time-reversal and/or proton-neutron symmetries are discussed and summarized in a tabulated form, useful in practical applications.

Isospin-invariant Skyrme energy-density-functional approach with axial symmetry

2014

We develop the isospin-invariant Skyrme-EDF method by considering local densities in all possible isospin channels and proton-neutron (p-n) mixing terms as mandated by the isospin symmetry. The EDF employed has the most general form that depends quadratically on the isoscalar and isovector densities. We test and benchmark the resulting p-n EDF approach, and study the general properties of the new scheme by means of the cranking in the isospin space. We extend the existing axial DFT solver HFBTHO to the case of isospin-invariant EDF approach with all possible p-n mixing terms. Explicit expressions have been derived for all the densities and potentials that appear in the isospin representatio…