NJOY+NCrystal: an open-source tool for creating thermal neutron scattering libraries

TL;DR

This paper introduces NJOY+NCrystal, an open-source tool that simplifies the creation of thermal neutron scattering libraries with support for both coherent and incoherent elastic components, enhancing neutron simulation capabilities.

Contribution

It presents a customized version of NJOY integrated with NCrystal, including format modifications and implementation in Monte Carlo codes, enabling advanced neutron scattering library generation.

Findings

Created 213 new and updated thermal scattering libraries.

Demonstrated application to materials like MgH₂ and MgD₂.

Enabled detailed modeling of coherent and incoherent elastic scattering.

Abstract

In this work we present NJOY+NCrystal, a tool to generate thermal neutron scattering libraries with support for coherent and incoherent elastic components for crystalline solid materials. This tool, which is a customized version of NJOY, was created by modifying the nuclear data processing program NJOY to call the thermal scattering software library NCrystal, and includes a proposed change in the ENDF-6 format to store both the coherent and incoherent elastic components. Necessary changes to enable this format in NJOY, as well as to sample it in the OpenMC Monte Carlo code, are detailed here. Examples of materials that are coherent-dominant, incoherent-dominant, and mixed elastic scatterers are presented, as well as the creation of novel libraries for MgH$_2$ and MgD$_2$, that are under consideration as advanced neutron reflectors in the HighNESS project at the European Spallation Source. NJOY+NCrystal simplifies greatly the process to generate thermal scattering libraries (TSL) and this is exemplified with 213 new and updated TSL evaluations.