Recent measurements of the $E2$ transition rate from the ground state to the first $2^{+}$ excited state of the proton dripline nucleus ${}^{36}\mathrm{Ca}$ show an unusual pattern when compared to its isotopic neighbor ${}^{38}\mathrm{Ca}$: despite having a higher $E_x\left(2_1^{+}\right)$ excitation energy, the $B(E2;0_1^{+}\to 2_1^{+})$ rate in ${}^{36}\mathrm{Ca}$ is larger. The question that naturally arises is to what extent this observation can be attributed to the unbound character of the $2_1^{+}$ state. To understand the influence of the continuum space on the low-energy properties of ${}^{36}\mathrm{Ca}$, we carried out Gamow shell model calculations that can account for the continuum coupling effects associated with the occupation of unbound $fp$ shells. We found that in the threshold $2^{+}$ state, ${}^{36}\mathrm{Ca}$ is spatially diffused, which impacts the observed $B\left(E2\right)$ trend.

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• Electromagnetic transitions
• Energy levels
• Nuclear many-body theory
• Nuclear structure & decays
• Shell model
• 20 ≤ A ≤ 38