Improved measurement of the 0₂⁺ → 0₁⁺ E0 transition strength for ⁷²Se using the SPICE spectrometer

The selenium isotopes lie at the heart of a tumultuous region of the nuclear chart where shape coexistence effects grapple with neutron-proton pairing correlations, triaxiality, and the impending proton drip line. In this work, a study of ⁷²Se by internal conversion electron and γ-ray spectroscopy was undertaken with the SPICE and TIGRESS arrays. New measurements of the branching ratio and lifetime of the 0₂⁺ state were performed, yielding a determination of ρ² (E0;0₂⁺→0₁⁺)=29(3) milliunits. Two-state mixing calculations were performed that highlighted the importance of interpretation of such E0 strength values in the context of shape coexistence.