Peninsulas of the neutron stability of nuclei in the vicinity of neutron magic numbers

Abstract

On the basis of the Hartree-Fock method as implemented with Skyrme forces (Ska, SkM * , Sly4, and SkI2) and with allowance for an axial deformation and nucleon pairing in the Bardeen-CooperSchrieffer approximation, the properties of extremely neutron-rich even-even nuclei were calculated beyond the neutron drip line known earlier from theoretical calculations. It was shown that the chains of isotopes beyond the neutron drip line that contain N = 32, 58, 82, 126, and 184 neutrons form peninsulas of nuclei stable against the emission of one neutron and, in some cases, peninsulas of nuclei stable against the emission of two neutrons. The neutron-and proton-density distributions in nuclei forming stability peninsulas were found to be spherically symmetric. A mechanism via which the stability of nuclei might be restored beyond the neutron drip line was discussed. A comparison with the results of calculations by the Hartree-Fock-Bogolyubov method was performed for long chains of sulfur and gadolinium isotopes up to the neutron drip line.

Peninsula of neutron stability of nuclei in the neighborhood of neutron magic number N = 126

“…On the basis of HF with Skyrme forces with allow ance for axial deformation (AD), we have shown [6][7][8][9][10][11][12][13][14] that beyond NDL limits, peninsulas can exist for nuclei with extremely high neutron excess in the neighborhood of magic numbers and new magic num bers N = 32, 58, 82, 126, 184, 258. It is noteworthy that the location of such peninsulas with respect to the N value in (N, Z) space does not depend on the choice of Skyrme forces.…”

“…As the number of neutrons grows in ENE isotopes, some states with high values of the orbital moment are introduced into the area of the dis crete spectrum of bounded states in proportion to fill ing, leading to the recovery of neutron stability. Allow ing for deformation expands the area of stable isotopes beyond NDL limits [9][10][11][12]. The strengthening of shell effects for rare earth neutron excess nuclei in the neighborhood of N = 126 was investigated in [15] on the basis of RHB theory and the Lagrangian model NL-SV1.…”

“…The basis parameters q = ω r /ω z and β 0 = [m( ω z ) 1/3 / ] 1/2 [8,18], chosen according to the con ditions of minimal total energy of the nuclei E(q, β 0 ), were optimized at each iteration. Optimizing q and β 0 is particularly important in performing calculations for slightly bounded neutron excess nuclei [11][12].…”

The new neutron rich nuclei

“…This method, however, implies a simple structure of the drip line, namely, that every line corresponding to a fixed number of protons on the nuclear chart crosses the neutron drip line only once. Yet, it might happen that the drip line has a more complicated structure [2,3,4,5,6,7,8,9,10,11]. In the vicinity of "magic" numbers or "quenched magic" numbers the following scenario can take place.…”

“…1. The analysis of the phenomenon of stability restoration through adding neutrons has been undertaken in [2,3,4,5,6,7,8,9,10,11], where long isotope rows of the elements Pb, Zr, Ar, Kr, Rn, Gd, Ba, S, U were considered. Thereby, the phenomenon of stability restoration through adding neutrons was in focus.…”