The effect of the tensor force of the energy spectra of N 14 and F 18 using realistic interactions

Abstract

A shell-model calculation has been done to determine the effect of the tensor force on the energy levels of N 14 and F 18. The interaction potential used was determined by the deuteron and low-energy scattering data and contained both central and tensor forces of Yukawa shapes in variable proportions. In both cases, it was found that the tensor force has a large effect on the energy levels. Although the results for the T = 1 states are in good agreement with experiment, the T = 0 states which are dependent on the tensor force are rather poor. The large discrepancies between the latter results and the observed ones were attributed to the lack of contribution to the energy matrices of the tensor force in the relative s-states in first order. The major effect of this zero contribution is to shift the ground-state level away from the experimental one. The energy differences between the various levels and the ground-state level showed that there may be an optimum central-tensor force mixture containing an appreciable tensor component which gives the observed level differences. The effect of higher order contributions from the tensor force were examined for the case of the mass 14 system by diagonalizing t-matrices which were obtained elsewhere. The level scheme obtained with these t-matrices was in reasonable agreement with experiment. The result indicates that a low-energy scattering potential would probably give the right results provided that the higher order contributions of the tensor force are properly taken into account.