Application of neutron-gamma analysis for determining compost C/N ratio

Authors: Yakubova, Galina; KAVETSKIY, ALEKSANDR - Auburn University; Prior, Stephen - Steve; Torbert, Henry - Allen

Submitted to: Compost Science and Utilization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2019
Publication Date: 7/31/2019
Citation: Yakubova, G.N., Kavetskiy, A., Prior, S.A., Torbert III, H.A. 2019. Application of neutron-gamma analysis for determining compost C/N ratio. Compost Science and Utilization. 27(3):146-160. https://doi.org/10.1080/1065657X.2019.1630339.
DOI: https://doi.org/10.1080/1065657X.2019.1630339

Interpretive Summary: The carbon to nitrogen ratio of compost is traditionally determined by laboratory analysis which is time consuming and labor intensive since it needs many samples that require extensive preparation before analysis. Neutron-gamma analysis can be an alternative method for measuring compost C/N ratio. This is a non-destructive in situ method that requires no sample preparation or sampling since it measures very large volumes of material relative to traditional methods. Neutron-gamma analysis was found to be able to measure the C/N ratio in compost up to values of 25 and greater.

Technical Abstract: The possible application of Pulsed Fast-Thermal Neutron Analysis (PFTNA) for determining the Carbon to Nitrogen ratio (C/N) of compost will be discussed. This analysis method has several advantages over traditional chemical analysis; it is a nondestructive in-situ method that does not require extensive sample collection and analyzes much larger volumes of material (~1 m3) than traditional chemical analysis (~1 cm3). The amount of carbon in compost can be determined by irradiating compost with neutrons and measuring the gamma ray peak at an energy of 4.44 MeV that appears due to inelastic scattering (INS). Nitrogen can be determined by measuring the gamma ray peak at 10.83 MeV that appears due to thermal neutron capture (TNC). For C/N measurements, a calibration line that relates the C/N mass ratio to the carbon/nitrogen gamma peak ratio should first be constructed; our calibration line was constructed using carbon-ammonium nitrate mixtures. Gamma spectra measurements can then be used to determine carbon and nitrogen peak values in order to utilize the calibration line for calculating the C/N mass ratio. The workability of this methodology has been demonstrated in laboratory experiments by calculating the C/N ratios for poultry litter and melamine. The applicability of PFTNA for compost C/N ratio determinations was evaluated with Monte-Carlo computer simulations of the neutron propagation in large compost volumes (Geant4 toolkit) and experimental measurements of INS and TNC gamma spectra of compost samples with a volume of 1.3 m3. Data from computer simulations and experiments demonstrated that the PFTNA method is fully applicable for determining the C/N ratio in compost material up to values of 25 and greater.