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The Footprint Characteristics of Cosmic Ray Thermal Neutrons
Author(s) -
Jakobi J.,
Huisman J. A.,
Köhli M.,
Rasche D.,
Vereecken H.,
Bogena H. R.
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2021gl094281
Subject(s) - footprint , neutron temperature , neutron , neutron probe , neutron detection , environmental science , cosmic ray , thermal , physics , nuclear physics , neutron cross section , meteorology , geology , paleontology
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.