Speaker
Description
The accurate knowledge of the neutron transport in air is particularly relevant for the optimized design of instrumentation, beam lines and shielding components, used for research, radioprotection or clinical applications. To simulate neutron transport and estimate dose delivery, Monte Carlo simulations are currently one of the most popular tools. Neutron transport simulations often rely on scattering cross sections that are calculated using the free gas model. However, in the thermal neutron energy range, this model provides a gross approximation, as neutron cross sections are greatly affected by the chemical and structural properties of materials.
In order to simulate the transport of thermal neutrons in air, we implemented the Young and Koppel model [1] for the thermal neutron cross sections of homonuclear diatomic molecules, such as N2 and O2, which are abundant in air. Moreover, the paramagnetic behaviour of molecular oxygen was taken into account for the calculation of its scattering cross section. The model obtained for air features a total scattering cross section about 4% higher than that of the free gas model at 25 meV; this difference increases up to 29% at 1 meV.
At present, our libraries are being included in Geant4 transmport simulations using the NCrystal module [2], with the purpose of comparing them to the free gas model and quantifying the impact of a specialized model.
References
[1] J. A. Young and J. U. Koppel, Phys. Rev., 1964, 135, A603–A611.
[2] Cai, X., Kittelmann, T.: Ncrystal: A library for thermal neutron transport. Computer Physics Communications 246, 106851 (2020)