New experimental data relevant to the shape change in the A ∼ 100 region

The shape change around the Z=40 proton and N=60 neutron numbers continues to attract the attention. Recent shell-model calculations, performed in a large base of single-particle orbits, have offered a new explanation of the effect as due to significant rearrangements of positions of these orbits. While the results are in many respects similar to conclusions based on the Nilsson scheme, there are also some differences, studying of which may help better understanding of the phase transition at Z=40, N=60. One of these differences concerns the role of the neutron 9/2⁺[404], extruder orbital, which is important in the Nilsson picture, in accord with its observation near the Fermi level in Sr and Zr isotopes around N=60. This orbital is, however, neglected in the shell-model approach, because of the νg(9/2) shell being located well below the valence shells. Another difference is related to the, generally, more important role of proton excitations in the shell-model picture in contrast to the employment of low- neutron subshells in the deformed, mean-field approach. It is clear that further detailed experimental search for proton and neutron excitations in the region is needed. Our previous works have shown the presence of low-Ω subshells of the νh(11/2) orbital and the ν(9/2⁺)[404] orbital [2] past the N=56 subshell closure. Less is know about the spherical g(7/2) and h(11/2) neutron orbitals in the 50 ≤ N ≤ 56 range as well as about low-Ω subshells of the πg(9/2) orbital above the N=56 subshell closure. Our recent studies of nuclei from the discussed region, utilizing the data measured with the Eurogam, Gammasphere, EXILL and FIPPS arrays of Ge detectors, the Lohengrin fission fragment separator and the JYFYLTRAP Penning trap provided new data on the subject, which will be presented and discussed in this paper. This document is composed of an abstract and the slides of the presentation. (authors)