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

TL;DR

Brightify addresses the lack of direct brightness computation in Monte Carlo neutron simulations by introducing a Python tool that computes directionally resolved brightness maps from MCPL data. It scans the recording surface with position windows, derives representative mean directions, and computes brightness using a phase-space normalization $B = \frac{\sum w_i}{N_p \Delta \Omega \Delta A}$, enabling identification of brightness hotspots and improved instrument alignment. Validation against surface current and point estimator tallies shows good agreement for uniform and symmetric sources and demonstrated gains when the local mean direction diverges from the tally normal (e.g., a representative 14% increase in tilted cases), highlighting Brightify’s ability to capture non-uniform brightness peaks. The tool reduces computational burden and enables rapid re-optimization of neutron sources and guides, with open-source availability on GitHub and planned enhancements for low-statistics robustness, parallelization, and adaptive resolution.

Abstract

Brightness is a critical metric for optimizing the design of neutron sources and beamlines, yet there is no direct way to calculate brightness within most Monte Carlo packages used for neutron source simulation. 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, facilitating the identification of positions and directions corresponding to maximum brightness. This functionality is particularly valuable for identifying brightness hotspots and helping fine-tune the design of neutron sources for optimal performance. We validate Brightify against standard methods, such as surface current tally and point estimator tally, and demonstrate its accuracy and adaptability, particularly in high-resolution analyses. By overcoming the limitations of traditional methods, Brightify streamlines neutron source re-optimization, reduces computational burden, and accelerates source development workflows. The full code is available on the Brightify GitHub repository.

Figures (6)

• Figure 1:
• Figure 2: Diagram for description of the point estimator tally from MCNP 6.3.0 manual. The point "r" can be from any place of the source kulesza_mcnp_2022.
• Figure 3: The flowchart for the Brightify algorithm.
• Figure 4: Maximum brightness as a function of phase space volume and the corresponding relative error, calculated by Brightify.
• Figure 5: Three test cases for validation of Brightify performance against conventional methods.