First Identification of Excited States in Zr 78 and Implications for Isospin Nonconserving Forces in Nuclei

At a fundamental level, the interactions between protons and protons, protons and neutrons, and neutrons and neutrons are not identical. Such isospin nonconserving interactions emerge when comparing the excitation energy of analog states in T=1 triplet nuclei. Here, we extend such an analysis to the A=78, T=1 triplet system - the heaviest system for which such complete data exists - and find strong disagreement with contemporary theory. This was achieved by pioneering the technique of recoil-β-β tagging to identify excited states in Zr78. We also established a Zr78 half-life of 25-8+17 ms and extended the T=1 band in Y78 to Jπ=(10+).