"The footprint characteristics of cosmic ray thermal neutrons" dataset of river experiment

The advance of the cosmic ray neutron (CRN) sensing method for estimating field scale soil moisture relied largely on simulations of the footprint properties of epithermal neutrons (~0.5 eV – 100 keV). Commercially available CRN probes are usually additionally equipped with a thermal neutron (< 0.5 eV) detector. The potential of these measurements is rarely explored because relevant features of thermal neutrons, such as the footprint and the sensitivity to soil moisture are unknown. Here, we used neutron transport modeling and a river crossing experiment to assess the thermal neutron footprint. We found that the horizontal thermal neutron footprint ranges between 43 and 48 m distance from the probe and that the vertical footprint extends to soil depths between 10 and 65 cm depending on soil moisture. Furthermore, we derived weighting functions that quantify the footprint characteristics of thermal neutrons. These results will enable new applications of thermal neutrons.面向田间尺度土壤含水率估算的宇宙射线中子（Cosmic Ray Neutron, CRN）探测方法的技术进步，高度依赖于对超热中子（~0.5 eV – 100 keV）探测足迹特性的模拟。目前商用的CRN探测器通常额外配备了热中子（<0.5 eV）探测器，但这类探测手段的应用潜力却鲜有挖掘，原因在于热中子的相关特性——如探测足迹及其对土壤含水率的响应灵敏度——尚不明确。本研究通过中子输运模拟与跨河实验，对热中子的探测足迹进行了评估。研究结果表明，热中子的水平探测足迹范围距探测器43至48米，而垂直探测足迹的土壤渗透深度则在10至65厘米之间，具体数值随土壤含水率变化。此外，本研究还推导得到了可量化热中子探测足迹特性的权重函数。上述研究成果将为热中子探测技术开辟全新的应用方向。