Collective-coupling analysis of spectra of mass-7 isobars:He7,Li7

Abstract

A nucleon-nucleus interaction model has been applied to ascertain the underlying character of the negative-parity spectra of four isobars of mass seven, from neutron-to proton-emitter driplines. With one and the same nuclear potential defined by a simple coupled-channel model, a multichannel algebraic scattering approach (MCAS) has been used to determine the bound and resonant spectra of the four nuclides, of which 7 He and 7 B are particle unstable. Incorporation of Pauli blocking in the model enables a description of all known spin-parity states of the mass-7 isobars. We have also obtained spectra of similar quality by using a large space no-core shell model. Additionally, we have studied 7 Li and 7 Be using a dicluster model. We have found a dicluster-model potential that can reproduce the lowest four states of the two nuclei, as well as the relevant low-energy elastic scattering cross sections. But, with this model, the rest of the energy spectra cannot be obtained.

Recent developments in Multi-Channel Algebraic Scattering calculations

“…2 were obtained with the same model described in Ref. [19]. That original calculation (reported also in second column of Table 3) perfectly describes 6 subthreshold states (out of 8 in total) but offsets the centroid of the measured 1.265 MeV In the left panel we compare our calculation with measurements taken at RIBRAS [16,21].…”

“…The decay into the α-3 H and α-3 He channels have been evaluated in Ref. [19]. Those MCAS calculations resulted in the ground and first excited states of the mass-7 nuclei being sub-threshold while the next two were resonances.…”

“…Those two resonance states lie below any other emission threshold and the MCAS widths agree well with the experimental ones. In [19], we also studied 7 He (as n+ 6 He) and the mirror system, 7 B (as p+ 6 Be). These compound systems lie beyond the relevant nucleon drip lines, with the ground state of 7 He being 0.445 MeV above the neutron breakup and with a width of 0.15 MeV.…”

The spectra of exotic light mass nuclei determined with MCAS theory

“…15 F is one such case [3]. The A = 7 system also has been considered with a unique nuclear potential, and the level structures of 7 He, 7 Li, 7 Be, and 7 B have been obtained [2]. We have also used the scheme to consider low energy properties of 3 H-and 3 He- 4 He scattering to correlate different views of the spectra of 7 Li and 7 Be.…”

“…The MCAS method [1,2] solves coupled channel LippmannSchwinger equations for a chosen two-body system. The theory is built upon sturmian expansions of whatever one chooses to be the interaction matrix of potential functions for the system.…”