Brightify: a tool for calculating directionally-resolved brightness in neutron sources

Brightness is a critical metric for optimizing the design of neutron sources and beamlines, yet most Monte Carlo packages do not offer a direct, directionally-resolved calculation. Conventional tallies require predefined locations and directions, limiting their ability to capture localized features or non-uniform emission. In this paper, we present Brightify, an open-source Python-based tool designed to calculate brightness from Monte Carlo Particle List (MCPL) files, which can be extracted from several Monte Carlo simulation packages. Brightify provides an efficient computational approach to calculate brightness for any particle type and energy spectrum recorded in the MCPL file. It enables localized, directionally-resolved brightness evaluations by scanning across both spatial and angular domains, using the mean direction within each position window as a representative direction. This functionality is particularly valuable for identifying brightness hotspots and helping fine-tune the design of neutron sources for optimal performance. Validation against standard surface current and point estimator tallies confirms Brightify's accuracy and demonstrates its added value in capturing features these methods miss. By addressing a methodological gap in brightness evaluation, Brightify offers a practical foundation for neutron source re-optimization, reduces computational burden, and accelerates source development workflows. The full code is available on the Brightify GitHub repository (Akhyani et al., 2025).