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Gargano, A.

Publications and source records attributed to Gargano, A..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Suppressed electric quadrupole collectivity in 49 Ti

Single-step Coulomb excitation of 46,48,49,50 Ti is presented. A complete set of E2 matrix elements for the quintuplet of states in 49 Ti, centred on the core excitation, was measured for the first time. A total of nine E2 matrix elements are reported, four of which were previously unknown. $^{49}_{22}$Ti 27 shows a 20% quenching in electric quadrupole transition strength as compared to its semi-magic $^{50}_{22}$Ti 28 neighbour. This 20% quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the 49 Ti- 50 Ti pair (i.e., approximate single-j 0 7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Shell-model study of calcium isotopes toward their drip line

Here, we report in this paper a study in terms of the nuclear shell model about the location of the calcium isotopes drip line. The starting point is considering the realistic two-body potential derived by Entem and Machleidt within chiral perturbation theory at next-to-next-to-next-to-leading order (N 3 LO), as well as a chiral three-body force at next-to-next-to-leading order (N 2 LO) whose structure and low-energy constants are consistent with the two-body potential. Then we construct the effective single-particle energies and residual interaction needed to diagonalize the shell-model Hamiltonian. The calculated two-neutron separation energies agree nicely with experiment until 56 Ca, which is the heaviest isotope whose mass has been measured, and do not show any sign of two-neutron emission until 70 Ca . We discuss the role of the choice of the model space in determining the neutron drip line, and also the dependence of the results on the parameters of the shell-model Hamiltonian.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Emerging nuclear collectivity in 124-130 Te

The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, eveneven 124-130Te isotopes. Preliminary measurements of the B(E2; 41+ → 21+) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 41+ states. Isotopically enriched Te targets were excited by 198-205 MeV 58Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.

coombes, Ben↗
DOE OSTI2020

Chiral three-nucleon force and continuum for dripline nuclei and beyond

Three-nucleon force and continuum play important roles in reproducing the properties of atomic nuclei around driplines. Therefore it is valuable to build up a theoretical framework where both effects can be taken into account to solve the nuclear Schrödinger equation. To this end, in this letter, we have expressed the chiral three-nucleon force within the continuum Berggren representation, so that bound, resonant and continuum states can be treated on an equal footing in the complex-momentum space. To reduce the model dimension and computational cost, the three-nucleon force is truncated at the normal-ordered two-body level and limited in the sd-shell model space, with the residual three-body term being neglected. We choose neutron-rich oxygen isotopes as the test ground because they have been well studied experimentally, with the neutron dripline determined. The calculations have been carried out within the Gamow shell model. The quality of our results in reproducing the properties of oxygen isotopes around the neutron dripline shows the relevance of the interplay between three-nucleon force and the coupling to continuum states. We also analyze the role played by the chiral three-nucleon force, by dissecting the contributions of the 2π exchange, 1π exchange and contact terms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Early Signal of Emerging Nuclear Collectivity in Neutron-Rich 129Sb

Radioactive 129Sb, which can be treated as a proton plus semimagic 128Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, B(E2), for the 2+Ⓧπg7/2 multiplet members and candidate πd5/2 state were measured. The results indicate that the total electric quadrupole strength of 129Sb is a factor of 1.39(11) larger than the 128Sn core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wave functions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.

Gray, Tim↗