Why kilonova brightness barely depends on which atoms decay?

When neutron stars merge, radioactive decay heats the expanding debris and ionizes atoms, making it glow. This work calculates how different decay particles (alphas, fission fragments, electrons) ionize the material. Surprisingly, the ionization efficiency is nearly identical across all decay channels and heavy-element compositions—a lucky cancellation of opposing physics that lets theorists ignore which isotopes dominate the decay chain when predicting kilonova spectra.