Low-Energy States inY90

Abstract

The low-energy levels of the odd-odd nucleus ${\mathrm{Y}}^{90}$ are calculated with finite-range central and tensor forces to first order by means of the $j-j$ coupled odd-group model. The two-body matrix elements for the central and tensor forces are expressed in the $j-j$ representation, from which a generalization to off-diagonal matrix elements is obtained in the limit of the zero range. A phenomenological Gaussian potential without a hard core, estimated from the free two-nucleon potentials of Jackson-Blatt and Brueckner-Gammel-Thaler, is used for the residual interaction. The effects of the tensor force are analyzed in detail as a function of the force range. The numerical results of the calculation are in reasonably good agreement with available experimental spectra.