In which isotope is the strong nuclear force not strong enough to balance electrostatic forces between protons?

In all nuclei above atomic number 83, the strong nuclear force is not strong enough to balance the electrostatic repulsion between protons. Nuclei like deuterium, carbon-13, and neon-21 are all stable. But elements like uranium-238 are radioactive. U-238 (Z = 92) has a half-life of about 4.5 billion years.