Odd-even staggering in neutron drip line nuclei

TL;DR

This study systematically investigates how different pairing force density dependencies affect odd-even staggering and neutron drip line properties in semi-magic nuclei using Hartree-Fock-Bogoliubov calculations.

Contribution

It compares local and global pairing strength schemes and analyzes their impact on neutron-rich isotopes and drip line predictions.

Findings

Surface pairing yields larger neutron gaps in certain isotopes.

Global pairing strengths reduce differences between pairing models.

Large gap differences are expected near the neutron drip line.

Abstract

We have done systematic Hartree-Fock-Bogoliubov calculations in coordinate space on the one-quasi-particle energies and binding energy odd-even staggering (OES) in semi-magic nuclei with the zero-range volume, mixed and surface pairing forces in order to explore the influence of their density dependence. The odd-$N$ isotopes are calculated within the blocking scheme. The strengths for the pairing forces are determined in two schemes by fitting locally to reproduce pairing gap in $^{120}$Sn and globally to all available data on the OES of semi-magic nuclei with $Z\geq8$. In the former calculations, there is a noticeable difference between the neutron mean gaps in neutron-rich O, Ca, Ni and Sn isotopes calculated with the surface pairing and those with the mixed and volume pairing. The difference gets much smaller if the globally optimized pairing strengths are employed. The heavier Pb isotopes show the opposite trend. Moreover, large differences between the mean gap and the OES may be expected in both calculations when one goes towards the neutron drip line.