- th / 0 00 70 18 v 1 1 0 Ju l 2 00 0 The Love - Hate Relationship Between the Shell Model and Cluster Models

We adopt a personal approach here reviewing several calculations over the years in which we have experienced confrontations between cluster models and the shell model. In previous cluster conferences we have noted that cluster models go hand in hand with Skyrme Hartee-Fock calculations in describing states which cannot easily, if at all, be handled by the shell model. These are the highly deformed (many particle-many hole) intruder states, linear chain states e.t.c. In the present work we will consider several topics; the quadrupole moment of 6 Li, the non-existence of low lying intruders in 8 Be, and then jumping to the f 7/2 shell, we discuss the two-faceted nature of the nuclei-sometimes displaying shell model properties, other times cluster properties. Whereas the quadrupole moment of the deuteron is positive(Q = +2.74mb), that of the J=1 + state of 6 Li is negative, Q=-0.818(17)mb. The magnetic moment of the deuteron is µ = 0.85741 mm while that of 6 Li is 0.822 mm. There appears to be a big discrepancy between cluster model calculations and the shell model calculations. In nearly all cluster model calculations Q comes out positive. However in many shell model calculations Q comes out negative, sometimes too negative. This is an important problem that deserves further attention. See for example arguments in the literature between the cluster group[1] and the shell model group[2]. See also the recent compendium of A=6 by D.R. Tilley et. al.[3]. For example in a modern shell model approach by Forest et. al. [4] gets about-8 mb for Q, a factor of 10 too large but of the correct sign. On the other hand in a dynamical 1