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Andreasen_et_al-2016-Water_Res ...
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FInal Published Version
Affiliation
Univ Arizona, Dept Hydrol & Water ResourcesIssue Date
2016-08Keywords
cosmic ray neutron intensity methodneutron transport modeling
cadmium difference method
neutron intensity profiles
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AMER GEOPHYSICAL UNIONCitation
Modeling cosmic ray neutron field measurements 2016, 52 (8):6451 Water Resources ResearchJournal
Water Resources ResearchRights
© 2016. American Geophysical Union. All Rights Reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
The cosmic ray neutron method was developed for intermediate-scale soil moisture detection, but may potentially be used for other hydrological applications. The neutron signal of different hydrogen pools is poorly understood and separating them is difficult based on neutron measurements alone. Including neutron transport modeling may accommodate this shortcoming. However, measured and modeled neutrons are not directly comparable. Neither the scale nor energy ranges are equivalent, and the exact neutron energy sensitivity of the detectors is unknown. Here a methodology to enable comparability of the measured and modeled neutrons is presented. The usual cosmic ray soil moisture detector measures moderated neutrons by means of a proportional counter surrounded by plastic, making it sensitive to epithermal neutrons. However, that configuration allows for some thermal neutrons to be measured. The thermal contribution can be removed by surrounding the plastic with a layer of cadmium, which absorbs neutrons with energies below 0.5 eV. Likewise, cadmium shielding of a bare detector allows for estimating the epithermal contribution. First, the cadmium difference method is used to determine the fraction of thermal and epithermal neutrons measured by the bare and plastic-shielded detectors, respectively. The cadmium difference method results in linear correction models for measurements by the two detectors, and has the greatest impact on the neutron intensity measured by the moderated detector at the ground surface. Next, conversion factors are obtained relating measured and modeled neutron intensities. Finally, the methodology is tested by modeling the neutron profiles at an agricultural field site and satisfactory agreement to measurements is found.Note
First Published: 25 August 2016; 6 Month Embargo.ISSN
00431397Version
Final published versionSponsors
Villum Foundation; European Union [213007]Additional Links
http://doi.wiley.com/10.1002/2015WR018236ae974a485f413a2113503eed53cd6c53
10.1002/2015WR018236