Since the nuclear interaction is, to first order, isospin independent, simple relationships can be derived for $E2$ strengths across isobaric analog states within an isobaric triplet. At the same time, there is a well-known relationship between the $2^{+}$ excitation energy and the $B(E2;2^{+}\to 0^{+}$) transition strength in deformed even-even nuclei. Here, we highlight a tension between these two trends in the $A=78$ isobaric triplet. Recent level-energy determinations indicate that the proton-rich member of the triplet, ${}^{78}\mathrm{Zr}$, is strongly deformed while recent lifetime measurements in ${}^{78}\mathrm{Sr}$ and ${}^{78}\mathrm{Y}$, as extrapolated into ${}^{78}\mathrm{Zr}$, would imply that ${}^{78}\mathrm{Zr}$ is weakly deformed. Here, we explore the implications of this apparent contradiction and explore potential solutions.

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• Collective levels
• Coulomb energies & analogue states
• Electromagnetic transitions
• Nuclear shapes and moments
• Nucleon distribution
• 59 ≤ A ≤ 89