GENERALIZED SENIORITY SCHEME IN LIGHT SN ISOTOPES

In search of a possible truncation scheme for shell model calculations , the yrast generalized seniority states are compared with the corresp onding shell model states for the case of the Sn isotopes Sn104-112. F or most of the cases the energies agree within a few hundred keV. For the 0(+)(2(+)) states the overlaps decrease from 97% (93%) in Sn-104 t o 91% (78%) in Sn-112 when the coefficients of the pairs in the S and D boson operators are allowed to vary with the number of particles. Fo r constant pairing coefficients throughout the entire isotope range, t he overlaps are considerably smaller. It is concluded, with the realis tic effective interaction applied here, that a truncation scheme based on seniority zero and two states is inadequate when the number of val ence particles gets large and that configurations of higher seniority should be included.