Spectroscopy of the light rare-Earth nuclei 133Pm and 133Sm: Configuration-dependent pairing and evidence for strong residual proton-neutron interactions in neighbouring odd-N and odd-Z nuclei

Abstract

The low-lying, rotational band structures of the highly neutron-deficient light rare-earth nuclei, 133Sm and 133Pm have been investigated using the 40Ca + 96Ru reaction at a beam energy of approximately 180 MeV. Five new bands have been observed in both nuclei. 133Sm possesss two strongly coupled bands which are thought to be built upon the vh112[523]72−and vd52[402]52+ Nilsson configurations. In addition to the previously reported vi132 intruder band, there is also evidence for a second decoupled, negative-parity structure in 133Sm based on the vh92[541]12− orbital. In 133Pm evidence is presented for both signature partners of the πh112 band. The expected h112 neutron alignment in these bands has not been observed. It is suggested that this provides evidence for a strong pn interaction. A strongly coupled band built on the πg72[413]52+ configuration has also been established. Both signature partners of this band show clear evidence for the alignment of a pair of h112 protons followed by a pair of h112 neutrons. A strongly coupled three quasi-particle configuration has also been identified which feeds into the unfavoured signature of the πh112 band. The results are discussed in terms of cranked shell model, total routhian surface calculations and the systematics of the A ∼ 135 region.