Preview

PDF, English - main document Download (23MB) | Terms of use

Abstract

Epithermal cosmic-ray neutrons are widely used as a proxy for environmental hydrogen content for an area of up to 20 hectares, reaching maximum soil penetration depths of 80 cm. The present work deploys the multi-particle Monte Carlo code MCNP6 to simulate neutron production via cosmic-ray particles and their transport processes at the land-atmosphere interface. The simulation setup was validated against measured neutron flux attenuation in water, air and soil and shows an accurate reproduction of the data sets. This led to simulation-fitted analytical functions that are designed for soil moisture sensing below the soil surface and snow water equivalent monitoring via cosmic-ray neutron detectors. Additionally, the influence of a homogeneous snow cover on the intensity and transport dynamics of the airborne epithermal neutron flux was examined and approximated by analytical functions. The limitations of standard cosmic-ray neutron detectors and the shortage of 3He have led to a novel gaseous 10B-lined neutron detector design specifically tailored to the needs of Cosmic-Ray Neutron Sensing. The system features high count rates as well as an adapted energy response, dedicated readout electronics and low pressure neutron counters, which results in low statistical and systematic errors of the epithermal neutron flux measurement. Two systems, stationary and mobile, proved to be able to capture soil moisture dynamics on the hectare and square kilometre scale.