Collective systematics in the mass 80 region

The deformation of nuclei around A∼80 is found to vary systematically as a function of the product of the number of protons and neutrons (or holes) ($N_{\mathrm{p}{N}_{\mathrm{n})}}$ in the shell extending from 28 to 50 particles. A similar result was reported previously for heavier even A nuclei, but this is the first investigation of a region in which neutrons and protons fill the same major shell and the first application of the technique to odd A nuclei. The systematic behavior is seen in both energy level spacings and electromagnetic quadrupole transition strengths and in both even-even and odd A nuclei. These systematics hold for the measures of deformation not involving the positions of the $0^{+}$ states, which are strongly affected by the coexistence of weakly and strongly deformed shapes in some A∼80 nuclei. A rather surprising result is that the deformations of the odd-Z–even-N nuclei are substantially larger than those of the even-Z–odd-N nuclei.