Geant4 and FLUKA Simulations of a Cyclotron Based 30 MeV Proton-Beryllium Reaction: Benchmarking and Optimization of Neutron Fields

TL;DR

This work benchmarks Geant4 and FLUKA for simulating a cyclotron-based $^9\mathrm{Be}(p,n)^{9}\mathrm{B}$ neutron source at $30\ \mathrm{MeV}$, focusing on target geometry, moderation, and neutron-field distribution. By aligning simulation parameters across tools, it assesses angular distributions, neutron fluence, and moderation efficiency using HDPE, and presents a modular irradiation station concept for generating thermal neutron fields. The results show general agreement at low neutron energies between Geant4 and FLUKA, with higher-energy divergences, and demonstrate how target tilt and moderator thickness strongly influence thermal neutron yield. The findings provide practical guidance for designing safe, adjustable neutron sources for research and testing in scenarios where reactors are unsuitable or unavailable.

Abstract

For studies where a reliable neutron source/beam is required and a nuclear reactor is not a viable option (considering their high neutron flux supply, which may not be suitable for research concerning low flux operations), alternative approaches may be sought. We present a comprehensive simulation analysis of 30 MeV proton induced ${}^9\mathrm{Be}\text{(p,n)}{}^9\mathrm{B}$ reaction, which can be utilized as an isotropic neutron source. This energy was chosen as it was the maximum allowed limit of protons supplied by IBA's Cyclone 30 XP proton cyclotron. Due to different underlying physics and transport mechanisms, when it comes to numerical calculations, slight variations in findings between different toolkits may occur. Hence it may require one to have a guide at hand to address the differences and interpret the data more accurately before conducting the actual experiment. In this work present the different numerical results of Geant4 and FLUKA. We conducted preliminary Monte Carlo runs to estimate the resulting neutron fluence and prompt gamma dose equivalents, while also assessing the degree of moderation achieved by different thicknesses of high density polyethylene. Furthermore, this work also presents an examplar modular irradiation station designed for target-moderator configurations, with the capability of generating thermal neutron fields.

Figures (17)

• Figure 1: Different incident proton energies were tested to get the neutron count coming out of an inclined target (left). Penetration depth of protons with respective energies (right). Geant4 and FLUKA
• Figure 2: Outer geometry showing moderator(green), lead casing and target-beam dump duo.
• Figure 3: Inner geometry showing beam dump (light blue) and target(dark blue).
• Figure 4: Top view of the constructed geometry using FLAIR and GeoViewer, graphical interface of FLUKA flair.
• Figure 5: A neutron funnel that was used by IVMER in previous neutron studies. Left is the mold, and right is the finished product. muçogllava_2022