INDEPENDENT NUCLEON-PAIR MOTION AND HOMOLOGOUS STRUCTURE IN NUCLEI WITH A-SIMILAR-TO-150

Shell model calculations are carried out for nuclei with 148 less than or equal to A less than or equal to 152 assuming Gd-146(64)82 as an i nert core. A weak coupling scheme is used to analyze the experimental data and the calculated results. The essential role of the proton intr uder state pi h(11/2), the large energy gaps between the neutron singl e-particle states vf(7/2) and the others, and the weak proton-neutron interaction provide a simple and interesting picture for the spectra a nd wave functions, i.e., the independent nucleon-pair motion and the c orresponding homologous structure. The proton pairs in pi h(11/2), pi d(3/2), and pi s(1/2) orbitals and the neutron pair in vf(7/2) or vf(7 /2)h(9/2) orbitals in nuclei Er-150,152(68)82,84 and Dy-150(60)84 are moving almost independently in the mean field provided by the core. Th erefore, the yrast states below 5.3 MeV of these nuclei can be finely explained as the compositions of the excitations of these independent nucleon pairs. The negative parity levels of nuclei Dy-146(66)83, Tb-1 49(65)84, Ho-151(67)84, and Tm-153(69)84 can be well interpreted in te rms of the concept of homologous states, i.e., the level structures in nuclei Dy-149(66)83, Tb-149(65)84, Ho-151(67)84, and Tm-153(69)84 are homologous to those of the parent structure in nuclei Dy-148(66)82, G d-148(64)84, Dy-150(66)84, and Er-152(68)84, respectively. The level s tructure of the nucleus Er-151(68)83, homologous to that of parent sta tes in the nucleus Er-150(68)82, is predicted and quite impressive in our full shell model calculation. This desires experiments to verify. The conditions for the onset of the independent nucleon-pair motion an d the homologous structure are discussed in detail.