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.

中文翻译：

---

宇宙线热中子的足迹特性

用于估计现场尺度土壤水分的宇宙射线中子 (CRN) 传感方法的进步在很大程度上依赖于对超热中子 (~0.5 eV–100 keV) 足迹特性的模拟。市售的 CRN 探头通常额外配备一个热中子 (<0.5 eV) 探测器。这些测量的潜力很少被探索，因为热中子的相关特征，例如足迹和对土壤水分的敏感性是未知的。在这里，我们使用中子传输模型和河流穿越实验来评估热中子足迹。我们发现水平热中子足迹范围在距探测器 43 到 48 m 的距离之间，垂直足迹延伸到 10 到 65 cm 的土壤深度，具体取决于土壤湿度。此外，我们导出了量化热中子足迹特征的加权函数。这些结果将使热中子的新应用成为可能。