  Neutron reflectometry is a critical tool for investigating the structure of
thin films and interfaces. However, the misapplication of the Born
approximation to reflection geometry leads some to assume that the minimum
thickness that may be probed by neutron reflectometry is limited by the Q-range
of the measurement. In this study, we use model-dependent analysis, multiple
isotopic contrasts, and magnetic spin states, to show that it is possible to
resolve structures significantly smaller than this perceived limit. To quantify
this "analytical resolution", we employ Bayesian model selection, offering a
robust and quantifiable comparison between different analytical models. We
believe that this work offers pivotal insights for the analysis of neutron
reflectometry and hope that it will contribute to more accurate and
information-rich analyses in the future.
