Shell and Pairing Effects in Spherical Nuclei Close to the Nucleon Drip Lines

Abstract

Until recently, the ground state binding energy of nuclei was most frequently calculated by using mass formulae of different types or by integrating finite difference equations derived from local mass relations. Typical approaches belonging to the first class are based on liquid drop model expressions with shell and pairing corrections [1–3]. The second methods [4–6] have been made possible by the considerable improvement of the experimental knowledge of the atomic masses during the two last decades [7–9]. Apart from least squares fits occuring at some stage, the above treatments are numerically rather simple accurate and rapid. Unfortunately, the reliability of their predictions for nuclei situated away from the valley of β-stability is questionable. This is connected to their high degree of phenomenology which does not allow to predict structural changes. On the other hand, as pointed out many times, several parameters of the liquid drop model cannot be determined with a sufficient accuracy (or even depend on the sample chosen for their adjustement) and consequently mass extrapolations are rather delicate.

Laboratoire associé au C.N.R.S