Quadrupole deformation of the self-conjugate nucleus $^{72}$Kr

We report on the first determination of the absolute $B(E2; 0^+_1 \rightarrow 2^+_1)$ excitation strength in the $N=Z$ nucleus $^{72}$Kr via intermediate-energy Coulomb excitation performed at the National Superconducting Cyclotron Laboratory at Michigan State University. $^{72}$Kr is the heaviest self-conjugate system for which this quantity has been measured. The deduced quadrupole deformation strength is compared to predictions of a variety of self-consistent models predicting shape coexistence. Large-scale shell-model Monte Carlo calculations reproduce the experimental $B(E2)$ value and link the result to the gap between the $fp$ and $gds$ major shells and the occupation of the deformation-driving $g_{9/2}$ orbit.