3 research outputs found
Spectroscopy of Na: shell evolution toward the drip line
Excited states in Na have been studied using the -decay of
implanted Ne ions at GANIL/LISE as well as the in-beam -ray
spectroscopy at the NSCL/S800 facility. New states of positive
(J=3,4) and negative (J=1-5) parity are proposed. The
former arise from the coupling between 0d protons and a 0d
neutron, while the latter are due to couplings with 1p or 0f
neutrons. While the relative energies between the J=1-4 states are
well reproduced with the USDA interaction in the N=17 isotones, a progressive
shift in the ground state binding energy (by about 500 keV) is observed between
F and Al. This points to a possible change in the proton-neutron
0d-0d effective interaction when moving from stability to the
drip line. The presence of J=1-4 negative parity states around 1.5
MeV as well as of a candidate for a J=5 state around 2.5 MeV give
further support to the collapse of the N=20 gap and to the inversion between
the 0f and 1p levels below Z=12. These features are discussed
in the framework of Shell Model and EDF calculations, leading to predicted
negative parity states in the low energy spectra of the F and O
nuclei.Comment: Exp\'erience GANIL/LISE et NSCL/S80
Spectroscopy of F to probe proton-neutron forces close to the drip line
A long-lived isomer, ms, has been discovered at 643.4(1)~keV in the weakly-bound F nucleus. It was populated at GANIL in the fragmentation of a S beam. It decays by an internal transition to the ground state (82(14)\%), by -decay to Ne, or beta-delayed neutron emission to Ne. From the beta-decay studies of the and states, new excited states have been discovered in Ne. Gathering the measured binding energies of the multiplet in F, we find that the proton-neutron effective force used in shell-model calculations should be reduced to properly account for the weak binding of F. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying states in F. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only