A Phenomenological Geometric Classification of Recurrent Mass Windows in LENR Transmutation Data

Several independent LENR transmutation data sets have reported the recurrent appearance of five relatively narrow mass regions across the periodic table. This empirical pattern, emphasized in recent reviews, remains without a widely accepted interpretation. Similar mass intervals have also been noted in compilations of electron-screening potentials obtained from low-energy deuteron fusion experiments. In this technical note, we adopt a deliberately phenomenological approach. We introduce a dimensionless geometric parameter defined as the ratio between the nuclear diameter and the electron Compton wavelength, and anchor five reference values to the empirically observed mass windows identified by Nagel, namely A = 12, 32, 66, 120, and 198. A simple distance metric Δ(A) is then used to quantify how closely each nucleus approaches these reference values. When applied systematically, this geometric classification provides a compact way to organize reported enhancement regions and extended intervals of relative suppression. No microscopic mechanism or reaction kinetics are assumed. The purpose of the present work is not to derive the origin of the mass windows, but to offer a reproducible and testable framework for organizing, comparing, and potentially predicting structure in LENR transmutation data, enabling systematic identification of preferred mass regions and their relation to material-dependent conditions.