Cluster correlations for low-lying intruder states of12Be

Abstract

The formation of intruder states in the low-lying states of 12 Be = α + α + 4N is studied by applying the generalized two-center cluster model, which can optimize the excess neutrons' orbits depending on the α-α distance. The correlation energy for the intruder states is analyzed from the viewpoint of two different pictures based on the cluster structure: the covalent picture around two α clusters and the binary He-cluster picture. In the covalent picture, the binding energy of (π − 3/2 ) 2 (σ + 1/2 ) 2 , corresponding to ν(0p) 4 (1s0d) 2 in a naive shell model, gains largely owing to the spin-triplet pairing of the 0d-wave neutrons, which is induced by the two-body spin-orbit interaction. The spin-triplet pairing gives rise to the reduction of the kinetic energy and the increase of the attractive spin-orbit interaction for the excess neutrons. As a result of these correlation energies, the ν(0p) 4 (1s0d) 2 configuration becomes dominant in the ground state. In the binary cluster picture, the correlation energy is investigated from the coupled channels among α + 8 He, 6 He + 6 He, and 5 He + 7 He. The coupling to 5 He + 7 He, which is neglected in usual binary-cluster models, plays an important role for a large reduction of kinetic energy and the formation of a pair of the low-lying 0 + states with a close energy spacing recently observed in experiment. The rotational bands are also discussed from the viewpoint of these two cluster pictures.

Helium-helium clustering states inBe12

“…The cluster structure in Be isotopes has gathered much attention in recent years, for their unique two-center symmetric system built on a well-established α + α rotor surrounded by a few valence neutrons [21][22][23][24]. Indeed the quenching of the N = 8 shell closure in 12 Be, observed in various experiments [25][26][27][28], can be well explained within an α-4n−α cluster model [22,23,29].…”

“…Indeed the quenching of the N = 8 shell closure in 12 Be, observed in various experiments [25][26][27][28], can be well explained within an α-4n−α cluster model [22,23,29]. Impressive progress on this topic has been made from the theoretical side, including antisymmetrized molecular dynamics (AMD) [30], the generator coordinate method (GCM) [31], and the generalized two-center cluster model (GTCM) [22][23][24].…”

Density functional theory studies of cluster states in nuclei

“…Low-energy structures in a number of relatively light neutron-rich nuclei can be described by molecular bonding (π or σ) of α-particles by the excess neutrons [30,31,33,[51][52][53][54][55][56]. Figure 7 displays the total, proton and neutron axially symmetric intrinsic densities of Be isotopes in their equilibrium configurations, calculated using the RHB model with the DD-ME2 functional.…”

16O + 16O + Valence Neutrons in Molecular Orbitals Structures of Positive- and Negative-Parity Superdeformed Bands in 34S

“…Sulfur isotopes are analogs of Be isotopes because those isotopes can form systems consisting of two doubly closed shell nuclei ( 16 O and α for S and Be isotopes, respectively) and valence neutrons. In Be isotopes, structures consisting of α + α + valence neutrons in molecular orbitals are thought to develop in low-lying states, with the valence neutrons in molecular orbitals around two α cores [4][5][6][7][8][9][10][11]. The SD states in 32 S are predicted to contain a large amount of 16 O + 16 O cluster structure components [2,3].…”