SHELL FORMATION AND DISAPPEARANCE IN EXOTIC NUCLEI AROUND N = 20

Abstract

The disappearance and the appearance of the magic numbers in N ∼ 20 unstable nuclei are discussed with large-scale shell-model calculations, most of which are the Monte Carlo shell model (MCSM) calculations. The MCSM calculations turn out to give a systematic description for this region. The origin of the shift of the magic structure from N =16 to 20 is shown to be the spin-isospin dependence of the nucleon-nucleon interaction giving rise to strongly attractive T =0 monopole interaction between the 0d5/2 and the 0d3/2. The extreme location of fluorine drip line can be understood from the viewpoint of the varying N =20 shell gap.