Investigation of the properties of nuclei with extreme neutron excess in the vicinity of neutron magic numbers

Abstract

Properties of even-even nuclei with extreme neutron excess in the vicinity of neutron magic num bers up to and beyond the neutron drip line (NDL) are calculated by the Hartree-Fock (HF) method using Skyrme forces (Ska, SkM*, Sly4, SkI2, SkP) with allowance for axial deformation and BCS approximation pairing. It is shown that chains of isotones with the neutron numbers N = 32, 58, 82, 126, 184, and 258 beyond the NDL form peninsulas of nuclei stable with respect to emission of one neutron, and occasionally penin sulas of nuclei stable with respect to the emission of two neutrons. The length of these peninsulas in (N, Z) space depends on the choice of the Skyrme forces, while their locations are at the same N = 32, 58, 82, 126, 184, and 258 and do not depend on the choice of forces. The investigated isotones restore stability beyond the NDL due to the complete filling of subshells with high angular momentum and to the intrusion of corre sponding neutron levels in the region of discrete bound states. The stability of the numerical solution to the HF equations for nuclei belonging to the peninsulas of stability is analyzed.

Light exotic nuclei with extreme neutron excess and 2 ≤ Z ≤ 8

“…This choice of pairing as well as the role of continuum states in the structure of nuclei lying at stability peninsulas is discussed in Refs. 11,12,13,14,15. Let us note that the inclusion of continuum states into present SHF calculations of nuclei with 2 ≤ Z ≤ 8, which form stability peninsula, did not affect the results that were obtained without inclusion of continuum states. This is, however, typical for magic and quasi-magic nuclei.…”

“…The neutron to proton ratio in 18 He and 40 C is N/Z = 8 and N/Z ≃ 5.67 respectively, which is substantially larger than the so far known neutron to proton ratios for stable nuclei. [9][10][11][12][13][14][15] Fig.1 also shows the stability peninsula consisting of one isotope 32 C. Later we shall discuss in detail the stability restoration for this isotope. Fig.…”

“…As we have mentioned such effect of stability restoration appears when neutron subshells with large angular momentum getting fully filled intrude from continuous spectrum into the bound spectrum. [11][12][13][14][15] (In 16 the formation of stability peninsulas was alternatively termed irregular behavior of the neutron drip line). Using SkI2 set of Skyrme forces we have found one stability peninsula situated at 18 He with the fully filled subshell 1d 5/2 and another one at 40 C with the fully filled subshell 1f 7/2 .…”

“…26 This is reasonable because nuclei belonging to stability peninsulas indeed possess spherical symmetry. [8][9][10][11][12][13][14][15] SHF calculations make possible the analysis of the role of continuum states in the cases when the DHF solution is spherically symmetric. We used the BCS constant pairing, where the pairing constant is set equal to G = (19.5/(N + Z))[1 ± 0.51(N − Z)/(N + Z)], 27 "+" and "-" correspond to protons and neutrons respectively.…”

“…[2][3][4][5][6][7] In Refs. 8,9,10,11,12,13,14,15 we explored the possibility of existence of islands and peninsulas of stability of nuclei with large neutron excess lying beyond the conventional neutron drip line. The calculations in these papers were done with the HF method using various type of effective Skyrme forces [17][18][19][20][21] and accounting for the axial deformation; the pairing was treated in the BCS scheme.…”