Two quasi-particle excitations with particle-hole core polarization in even-even single closed shell nuclei

2014 The energies and transition properties of the even-even N = 28, 50 isotones and Z = 28, 50, 82 isotopes are calculated in the framework of the Tamm-Dancoff and Random Phase Approximation, with an effective central interaction in an extended space consisting of two quasiparticle configurations for the open shell and particle-hole configurations for the closed core. Using the results of the Inverse Gap Equation Method, practically all the necessary input data (single quasi-particle energies, force strength) are extracted from the odd-mass nuclei. The ratios of the force components are kept to fixed values for all studied nuclei and no effective charge is used. An overall excellent agreement is obtained for the energies of the vibrational states. On the other hand, while the transition properties of the 3states are always well reproduced, those of the 2+ and 4+ states are often too small by about one order of magnitude. LE JOURNAL DE PHYSIQUE TOME 37, MARS 1976, 1