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Title: Advanced in-situ measurement of soil carbon content using inelastic neutron scattering

item Yakubova, Galina
item KAVETSKIY, ALEXANDER - Auburn University
item Torbert, Henry - Allen
item Prior, Stephen - Steve

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/3/2014
Publication Date: 9/3/2014
Citation: Yakubova, G.N., Kavetskiy, A., Torbert III, H.A., Prior, S.A. 2014. Advanced in-situ measurement of soil carbon content using inelastic neutron scattering [abstract]. Complex Soil Systems Conference: A Path to Improved Understanding of Complex Soil Systems. p. 63.

Interpretive Summary:

Technical Abstract: Measurement and mapping of natural and anthropogenic variations in soil carbon stores is a critical component of any soil resource evaluation process. Emerging modalities for soil carbon analysis in the field is the registration of gamma rays from soil under neutron irradiation. The inelastic neutron scattering (INS) of fast neutrons (with energy around 14 MeV) on carbon-12 nuclei produces gamma rays with energy of 4.43 MeV and the registration of this gamma flux can be directly used for determination of carbon contained in soil. The INS method has several advantages over other methods of carbon determination like dry combustion, laser induced breakdown spectroscopy, mid and near infrared reflectance spectroscopy. The INS method is non-destructive, requires no sample preparation, and analyzes a large soil volume in a single measurement. Due to these features the INS method can be applied for in-situ routine soil carbon determination. Currently this method is in development at the USDA-ARS National Soil Dynamics Laboratory. Previous findings from Brookhaven National Laboratory (Wielopolski et al., 2000-2012) were utilized to facilitate the physical construction and electronic requirements of a mobile INS system (MINS) for carrying out routine field measurements. The MINS power system (consisting of four 12V batteries with 105Ah, a DC-AC inverter, and a charger) is capable of powering a MP320 neutron generator, a neutron detector, three 12.7 cm x 12.7 cm x 15.2 cm scintillation NaI (Tl) detectors with corresponding electronics, and the laptop computer that controls the neutron generator, detectors, and data acquisition. The MINS was designed to operate on a platform that can be maneuvered by tractors or all-terrain vehicles over any type of field. Using MINS, measurements of the 4.43 MeV gamma peak were conducted at 28 field sites. For carbon in the 0-30 cm soil layer, a comparison of the corrected 4.43 MeV peak (i.e., overlapping gamma peaks due to other carbon-12 nuclei and processes) with chemical analysis (dry combustion method) showed a direct correlation. The MINS was operated in two modes – pulse and continuous. Comparison of these modes for carbon measurement accuracy was conducted using sand/carbon mixtures (40 cm ×40 cm ×20 cm) representing various carbon percentages. Since the measurement time in the continuous mode was half that of the pulse mode with the same accuracy, the continuous mode was preferable for routine soil carbon measurements. To further access the possibility of in-situ carbon measurement in the continuous mode, MINS was calibrated using 1.5 m×1.5 m×0.6 m boxes filled with soil mixtures of known carbon percentages. Collectively, this information will be used in future field studies to evaluate the ability of MINS to obtain in-situ measurements of soil carbon.