Penning-trap mass spectrometry and mean-field study of nuclear shape coexistence in the neutron-deficient lead region

Abstract

We present a study of nuclear shape coexistence in the region of neutron-deficient lead isotopes. The midshell gold isotopes ^{180,185,188,190}Au (Z=79), the two long-lived nuclear states in ¹⁹⁷At (Z=85), and the neutron-rich nuclide ²¹⁹At were produced by the ISOLDE facility at CERN and their masses were determined with the high-precision Penning-trap mass spectrometer ISOLTRAP. The studied gold isotopes address the trend of binding energies in a region of the nuclear chart where the nuclear charge radii show pronounced discontinuities. Significant deviations from the atomic-mass evaluation were found for ^188,190Au. The new trend of two-neutron separation energies is smoother, although it does reveal the onset of deformation. The origin of this effect is interpreted in connection to the odd-even staggering of binding energies, as well as theoretically by Hartree-Fock-Bogoliubov calculations including quasiparticle blocking. The role of blocking for reproducing the large odd-even staggering of charge radii in the mercury isotopic chain is illustrated

Nuclear deformation in the A≈100 region: Comparison between new masses and mean-field predictions

“…Because of its essential role in the Federman-Pittel mechanism [56], the pairing force had to be adjusted in the calculations to reproduce the nuclear deformation. Similarly to the works presented in [23] and [57], in the current work the pairing interaction was tuned on the odd-even staggering of the binding energies of Sn isotopes between N = 67 and N = 73, in a spherical calculation. An equal pairing interaction of −200 MeVfm 3 was chosen for protons and neutrons.…”

Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

“…As explicitly noted in [79], the precise staggering pattern depends sensitively on the details of the effective interaction. This can be explicitly demonstrated by comparing results for the SLy4 parameterization from all three sources, [77,78] and [79], which differ in the pairing interaction employed in the respective calculations. Altogether, the past DFT investigations led to an overall understanding of the physics of the phenomenon.…”

“…In [78] the shape coexistence in the region was confirmed as a mechanism for the observed radius staggering for the SLy4, Sk3 and SGII parameterizations with fixed gap parameters, although the exact staggering could not be reproduced. In [79], the SLy4 parameterization was again employed, but this time with a pairing strength adjusted to the odd-even staggering of the lead isotopes, leading to a qualitative correct staggering that is off by four neutron numbers. As explicitly noted in [79], the precise staggering pattern depends sensitively on the details of the effective interaction.…”

“…In [79], the SLy4 parameterization was again employed, but this time with a pairing strength adjusted to the odd-even staggering of the lead isotopes, leading to a qualitative correct staggering that is off by four neutron numbers. As explicitly noted in [79], the precise staggering pattern depends sensitively on the details of the effective interaction. This can be explicitly demonstrated by comparing results for the SLy4 parameterization from all three sources, [77,78] and [79], which differ in the pairing interaction employed in the respective calculations.…”