Soil Moisture and Air Humidity Dependence of the Above-Ground Cosmic-Ray Neutron Intensity

被引:40
作者
Koehli, Markus [1 ,2 ]
Weimar, Jannis [1 ]
Schroen, Martin [3 ]
Baatz, Roland [4 ]
Schmidt, Ulrich [1 ]
机构
[1] Heidelberg Univ, Phys Inst, Heidelberg, Germany
[2] Univ Bonn, Phys Inst, Bonn, Germany
[3] UFZ Helmholtz Ctr Environm Res, Leipzig, Germany
[4] Forschungszentrum Julich, Agrosphere IBG 3, Julich, Germany
来源
FRONTIERS IN WATER | 2021年 / 2卷
关键词
Monte Carlo; neutron; soil moisture; air humidity; cosmic-ray neutron sensing; MCNP; URANOS; NUCLEAR-DATA; ENERGY-SPECTRUM; CALIBRATION; SENSORS; QUANTIFICATION; VALIDATION; FISSION; SCIENCE; MODEL; PROBE;
D O I
10.3389/frwa.2020.544847
中图分类号
TV21 [水资源调查与水利规划];
学科分类号
081501 ;
摘要
Investigations of neutron transport through air and soil by Monte Carlo simulations led to major advancements toward a precise interpretation of measurements; they particularly improved the understanding of the cosmic-ray neutron footprint. Up to now, the conversion of soil moisture to a detectable neutron count rate has relied mainly on the equation presented by Desilets and Zreda in 2010. While in general a hyperbolic expression can be derived from theoretical considerations, their empiric parameterization needs to be revised for two reasons. Firstly, a rigorous mathematical treatment reveals that the values of the four parameters are ambiguous because their values are not independent. We found a three-parameter equation with unambiguous values of the parameters that is equivalent in any other respect to the four-parameter equation. Secondly, high-resolution Monte-Carlo simulations revealed a systematic deviation of the count rate to soil moisture relation especially for extremely dry conditions as well as very humid conditions. That is a hint that a smaller contribution to the intensity was forgotten or not adequately treated by the conventional approach. Investigating the above-ground neutron flux through a broadly based Monte-Carlo simulation campaign revealed a more detailed understanding of different contributions to this signal, especially targeting air humidity corrections. The packages MCNP and URANOS were used to derive a function able to describe the respective dependencies, including the effect of different hydrogen pools and the detector-specific response function. The new relationship has been tested at two exemplary measurement sites, and its remarkable performance allows for a promising prospect of more comprehensive data quality in the future.
引用
收藏
页数:15
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