Realistic Effective Interaction between Nucleons in Cluster States of Light Nuclei: Starting-Energy-Dependent Interaction and Its Application to Alpha-Cluster plus 16O-Core Model of 20Ne

Abstract

471With the aim of studying clustering problems in light nuclei on the basis of the characteristic properties of realistic nuclear forces, a starting-energy-dependent interaction is presented as a realistic effective interaction which simply represents the state-dependence of the reaction matrix caused by the triplet-even tensor force. This interaction is applied to the. alpha-cluster plus "0-core model of 20 Ne and compared with results for Volkov forces. It is shown that the starting-energy-dependence of the former acts to enhance alpha-clusterization with a mechanism different from the strong odd state repulsions of the latters. A density-dependence of an effective interaction. due to the short-range-repulsive core is further incorporated so as to assure the overall-saturation. A preliminary application to the 16 0-"0 system is made successfully. § I. IntroductionRecent experimental and theoretical studies have revealed the extensive existence of the states with cluster structure in light nuclei_l> In many cases these cluster states exist in the same energy region as normal shell model states. Such coexistence of shell and cluster states is a characteristic. manifestation of the nuclear saturation property, which leads to almost the same binding energy per particle in both states. Therefore, it is necessary to study cluster structures on the basis of our knowledge of the nuclear saturation mechanism.Some phenomenological effective interactions with simple exchange characters, e.g., V olkov forces, have been used in most of microscopic cluster model calculations. 1 )' 2 l In the case of these interactions the saturation property is assured, though only. for a few number of nuclei, by unrealistically strong repulsions in odd states. Strong odd state repulsions are known to enhance clusterization in a nucleus. On the other hand, investigations by the reaction matrix theory have . clarifi~d that the nuclear saturation is mainly attributable to the short-range repulsive core and the strong tensor part in realistic nuclear forces. In particular the overaU saturation from the a-particle to infinite nuclear matter can be realized mainly by the shielding effect of the triplet-even tensor force, which means that the relative weight of the tensor force contributions 1s strongly reduced by many-body effects with increase of mass number. 3 > Od 1 -2.12 *' This is made, for example, by taking the path of the inversion motion as the generator coordinate together with the relative motion between alpha-cluster and 1 '0-core. 11 '