Spectroscopy of 26F to probe proton-neutron forces close to the drip line
By A. Lepailleur - GANIL
A long-lived Jp=41+ isomer, T1/2=2.2(1)ms, has been discovered at 643.4(1) keV in the weakly-bound 26 9F nucleus. It was populated at GANIL in the fragmentation of a 36S beam. It decays by an internal transition to the Jp=11+ ground state (82(14)%), by b-decay to 26Ne, or beta-delayed neutron emission to 25Ne. From the beta-decay studies of the Jp=11+ and Jp=41+ states, new excited states have been discovered in 25,26Ne. Gathering the measured binding energies of the Jp=11+-41+ multiplet in 26 9F, we find that the proton-neutron p0d5/2 n0d3/2 effective force used in shell-model calculations should be reduced to properly account for the weak binding of 26 9F. 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 11+,21+,41+ states in 26F. 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.