nuclear physics - Which nucleus is the most resilient against gamma-induced fission?

To state the title question perhaps more precisely:

What is the largest photon energy $E_{\gamma}$ and the corresponding mass number $A$ and atomic number $Z$ of a suitable nucleus ${}^A_ZX$ (presumably in a ground state) such that the hypothetical reaction

$$ {}^A_ZX + \gamma \rightarrow {}^{(A - a)}_{(Z - z)}Y + \text{whatever remains (with combined charge} +z \text{)}$$

is "kinematically" forbidden for any values $1 \le a < A$ and $Z \ge z \ge Z + a - A$,
while conforming to the standard model?

Edit
Changed the question title (removed the parenthetical qualification "whether otherwise stable or not"): for any unstable nucleus the stated question and condition is not meaningful and not relevant.