Energy level statistics in particle-rotor model

Energy level statistics of a system consisting of six particles interacting by delta force in a two-j model coupled with a deformed core is studied in particle-rotor model. For single-j shell (i_13/2) and two-j shell (g_7/2 + d_5/2) the exact energies for our statistical analysis are obtained from a full diagonalization of the Hamiltonian, while in two-j case (i_13/2 + g_9/2) the configuration truncation is used. The nearest-neighbor distribution of energy levels and spectral rigidity are studied as the function of spin. The results of single-j shell are compared with those in two-j case. It is showed that the system becomes more regular when single-j space (i_13/2) is replaced by two-j shell (g_7/2 + d_5/2) although the basis size of the configuration space is unchanged. The degree of chaoticity of the system, however, changes slightly when configuration space is enlarged by extending single-j shell (i_13/2) to two-j shell (i_13/2 + g_9/2).