Response Functions for Detectors in Cosmic Ray Neutron Sensing

TL;DR

This paper investigates the response functions of neutron detectors used in Cosmic-Ray Neutron Sensing, using Monte Carlo simulations to improve understanding of detector sensitivity and angular response for environmental water content measurement.

Contribution

It provides detailed response functions for CRNS detectors across neutron energies and angles, enhancing modeling accuracy for environmental neutron transport studies.

Findings

Detectors are most sensitive to vertical neutron fluxes.

Good agreement with Bonner Sphere reference data.

Response functions cover neutron energies from 0.1 eV to 1 MeV.

Abstract

Cosmic-Ray Neutron Sensing (CRNS) is a novel technique for determining environmental water content by measuring albedo neutrons in the epithermal to fast energy range with moderated neutron detectors. We have investigated the response function of stationary and mobile neutron detectors typically used for environmental research in order to improve the model accuracy for neutron transport studies. Monte Carlo simulations have been performed in order to analyze the detection probability in terms of energy-dependent response and angular sensitivity for different variants of CRNS detectors and converter gases. Our results reveal the sensor's response to neutron energies from 0.1 eV to 1 MeV and highest sensitivity to vertical fluxes. The detector efficiency shows good agreement with reference data from the structurally similar Bonner Spheres. The relative probability of neutrons contributing to the overall integrated signal is especially important in regions with non-uniform albedo fluxes, such as complex terrain or heterogeneous distribution of hydrogen pools.