Pairing correlations in nuclei on the neutron-drip line

Abstract

Paring correlations in weakly bound nuclei on the edge of neutron drip line is studied by using a three-body model. A density-dependent contact interaction is employed to calculate the ground state of halo nuclei $^{6}$He and $^{11}$Li, as well as a skin nucleus $^{24}$O. Dipole excitations in these nuclei are also studied within the same model. We point out that the di-neutron type correlation plays a dominant role in the halo nuclei $^{6}$He and $^{11}$Li having the coupled spin of the two neutrons $S$=0, while the correlation similar to the BCS type is important in $^{24}$O. Contributions of the spin $S$=1 and S=0 configurations are separately discussed in the low energy dipole excitations.Comment: 6 pages, 12 eps figure

Strong dineutron correlation inHe8andC18

“…Before we do this, however, we first examine the applicability of the HFB method by applying it to the three-body model of 6 He nucleus [6,26]. This model has been solved exactly by diagonalizing the Hamiltonian matrix.…”

“…In Refs. [6,26], the center of mass motion is treated exactly by introducing the recoil kinetic energy of the core nucleus (see Ref. [14] for the derivation of the recoil term).…”

“…We solve the HFB equations (12) self-consistently by expanding the HFB wave functions on the eigen functions of the mean-field Hamiltonianĥ [31]. In doing so, we respect the Pauli principle and explicitly exclude those states which are occupied by the neutrons in the core nucleus.…”

“…Although the dineutron structure as a consequence of the pairing correlation has been suggested for some time in 11 Li and 6 He nuclei [1,3], it is only recently that a strong indication of its existence has been obtained experimentally in the Coulomb dissociation of 11 Li [4]. The new measurement has stimulated lots of theoretical discussions on the dineutron correlation, not only in the 2n halo nuclei, 11 Li and 6 He [5,6,7,8], but also in medium-heavy neutronrich nuclei [9,10] as well as in infinite neutron matter [11,12].…”

“…In Sec. III, we apply the method to 6 He, where the result of the exact diagonalization of the three-body (α+n+n) Hamiltonian has been obtained [6,26]. We compare the HFB result with the exact result, and discuss the applicability of the HFB method for the study of the spatial structure of valence neutrons.…”