Empirical Benchmarking of ΔN = 2 Half-Life Staggering in Ground-State Nuclides (Z = 2–98)

I identify a simple pattern in evaluated isotope half-life trends as a function of neutron number that I call the 2-neutron stability shoulder. For each element, I define a stable band as the interval in mass number spanned by the element’s lightest and heaviest observationally stable isotopes. For elements with no observationally stable isotopes, I instead define an effective stability band using all isotopes of that element with half-life years[1], taking the band to be the interval from the lightest to the heaviest isotope meeting that threshold. On the neutron-poor and neutron-rich sides of the resulting band, I select a representative wing isotope by taking the longest-lived radioactive nuclide on that side, breaking ties in favor of the nuclide closest to the band edge. For each wing, I then test whether moving toward the band by neutrons produces a nuclide with a longer half-life, or reaches observational stability (when present). Using evaluated ground-state half-lives from NUBASE2020, I benchmark for elements with that have at least one isotope with years. Under this definition, is the dominant step size on both wings. For the elements for which both wings are defined and the required stepped-to nuclides exist in the dataset, yields zero “neither” cases: every element has at least one wing where the step increases half-life (or reaches observational stability when applicable), and a majority improve on both wings simultaneously. I compare against and discuss interpretations consistent with odd–even (pairing) systematics and the geometry of the valley of stability. [1] Thus the following Elements are excluded: Pm (61), Po (84), At (85), Rn (86), Fr (87), Ra (88), Ac (89)