Why are all transuranium elements radioactive?

All transuranium elements—those with atomic numbers greater than 92—are radioactive because they are inherently unstable.1

The stability of an atomic nucleus depends on the balance of forces between its constituent protons and neutrons. As the number of protons increases, the electrostatic repulsion between them grows, which destabilizes the nucleus. For these heavy elements, this repulsion becomes so significant that the nuclei cannot remain intact indefinitely, leading them to decay through processes such as alpha-particle emission and spontaneous fission.23

While nuclear stability is influenced by the arrangement of nucleons into shells, transuranium elements generally lack the configurations required for long-term stability. Their nuclei exist in a state of relative instability, with half-lives ranging from millions of years to mere fractions of a second. Although theoretical models suggest the potential existence of an "island of stability" near specific magic numbers of protons and neutrons, all currently known transuranium isotopes remain subject to radioactive decay.31