Emergence of nuclear clustering in electric-dipole excitations ofLi6

Abstract

Nuclear clustering plays an important role, especially in the dynamics of light nuclei. The importance of the emergence of the nuclear clustering was discussed in the recent measurement of the photoabsorption cross sections as it offered the possibility of the coexistence of various excitation modes which are closely related to the nuclear clustering. To understand the excitation mechanism, we study the electric-dipole (E1) responses of 6 Li with a fully microscopic six-body calculation. The ground-state wave function is accurately described with a superposition of correlated Gaussian (CG) functions with the aid of the stochastic variational method. The final-state wave functions are also expressed by a number of the CG functions including important configurations to describe the six-body continuum states excited by the E1 field. We found that the out-of-phase transitions occur due to the oscillations of the valence nucleons against the 4 He cluster at the low energies around 10 MeV indicating "soft" giant-dipole-resonance(GDR)-type excitations, which are very unique in the 6 Li system but could be found in other nuclear systems. At the high energies beyond ∼ 30 MeV typical GDR-type transitions occur. The 3 He-3 H clustering plays an important role to the GDR phenomena in the intermediate energy regions around 20 MeV.

Electric-dipole transitions in 6Li with a fully microscopic six-body calculation

“…Considering the fact that the S 2 ht values are large 0.7 (see Table 1), this behavior can be interpreted as the E1 excitation of the relative wave function between the h and t clusters. Actually, the peak positions are located at ∼2 fm, which is about the sum of the peak positions of the densities of h and t [3].…”

“…The results with u = 0.93 are adopted from the data given in Ref. [3]. To discuss more details on the transition densities, here we discuss the isoscalar dipole excitation whose operator is defined by [20].…”

“…Basically, this contribution aims at reviewing the discussions and findings given in Ref. [3] accompanying with some unpublished results. We calculate the E1 transition strengths and their transition densities and discuss how 6 Li is excited by the E1 field as a function of the excitation energy.…”

“…Excitation energy E x in MeV, B(E1) in e 2 fm 2 and α + p + n and h + t spectroscopic factors in6 Li with different u parameters. The results with u = 0.93 are adopted from Ref [3]…”

Report on scipost_201912_00021v1

“…The results with u = 0.93 are adopted from the data given in Ref. [3]. To discuss more details on the transition densities, here we discuss the isoscalar dipole excitation whose operator is defined by [18].…”