High-accuracy Geant4 simulation and semi-analytical modeling of nuclear resonance fluorescence

TL;DR

This paper improves the accuracy of Geant4-based nuclear resonance fluorescence simulations by replacing Gaussian approximations with full numerical integration and developing a semi-analytical model, achieving agreement within 3%.

Contribution

It introduces a full numerical integration method for NRF cross sections and a semi-analytical model, enhancing simulation accuracy in Geant4 for complex geometries.

Findings

Agreement within 1% in simple cases

Agreement within 3% in complex scenarios

Significant accuracy improvement over previous methods

Abstract

Nuclear resonance fluorescence (NRF) is a photonuclear interaction that enables highly isotope-specific measurements in both pure and applied physics scenarios. High-accuracy design and analysis of NRF measurements in complex geometries is aided by Monte Carlo simulations of photon physics and transport, motivating Jordan and Warren (2007) to develop the G4NRF codebase for NRF simulation in Geant4. In this work, we enhance the physics accuracy of the G4NRF code and perform improved benchmarking simulations. The NRF cross section calculation in G4NRF, previously a Gaussian approximation, has been replaced with a full numerical integration for improved accuracy in thick-target scenarios. A high-accuracy semi-analytical model of expected NRF count rates in a typical NRF measurement is then constructed and compared against G4NRF simulations for both simple homogeneous and more complex heterogeneous geometries. Agreement between rates predicted by the semi-analytical model and G4NRF simulation is found at a level of ${\sim}1\%$ in simple test cases and ${\sim}3\%$ in more realistic scenarios, improving upon the ${\sim}20\%$ level of the initial benchmarking study and establishing a highly-accurate NRF framework for Geant4.