Evidence Found for a New Type of Radioactivity: Two-Proton Emission

The interplay between the nuclear forces and the electromagnetic force determines whether a given combination of protons and neutrons can stay together long enough to be called a nucleus. Even then, some nuclei are sufficiently unstable that, sooner or later, they undergo fission or decay. It stands to reason that a proton-rich nucleus might strive to shed a few protons. Indeed, back in 1960, Vitalii Goldanskii predicted that proton-rich nuclei having even values of atomic number Z could decay by emitting two protons. ¹ Iron-45 was among the rare candidates in which Goldanskii predicted one might see such two-proton decay. Iron-45, having 11 fewer neutrons than the most common isotope of iron, has only recently been produced in heavy-ion accelerators. Now, research teams at the Laboratory for Heavy-Ion Research (GSI) in Darmstadt, Germany, and at GANIL, a national heavy-ion accelerator in Caen, France, have independently formed ⁴⁵Fe and found...