Structure of A=138 isobars above the 132Sn core and the N-N interaction in the neutron-rich environment
Large basis untruncated shell model calculations have been done for the A=138 neutron -rich nuclei in the pi(gdsh) X nu(hfpi) valence space above the 132Sn core. Two (1+2) -body nuclear Hamiltonians, viz., realistic CWG and empirical SMPN in this model space have been used. Calculated ground state binding energies, level spectra and other spectroscopic properties have been compared with the available experimental data. Importance of untruncated shell model calculations in this model space has been pointed out. Shell model results for the very neutron rich Sn isotope (138Sn, N/Z=1.76) of astrophysical interest for which no spectroscopic information except beta -decay half life is available, have been presented. Shell structure and evolution of collectivity in the even-even A=138 isobars have been studied as a function of valence neutron and /or proton numbers. Calculations done for the first time, reproduce remarkably well the collective vibrational states in 138Te and 138Xe. Comparison of some of the important two-body matrix elements of the empirical SMPN, CW5082 and the realistic CWG interactions has been done. These matrix elements are important for ground state binding energies and low-lying spectra of nuclei in this region. Consideration of the predictability of the two interactions seems to suggest that, in order to incorporate the special features of the N-N interaction in such exotic n-rich environment above the 132Sn core, the use of local spectroscopic information from the region might be essential.