Application of Neutron-Gamma Analysis for Determination of C/N Ratio in Compost.

Neutron-gamma analysis is based on gamma ray acquisition from neutron irradiated objects. The intensity and energy of registered gamma rays yields information on types and amounts of elements in objects. Previous use of this method for soil C measurements demonstrated effective application in soil science due to advantages over traditional laboratory chemical methods. Neutron gamma analysis is a nondestructive in situ method that requires no sample preparation and can perform multi-elemental analyses of large soil volumes in ~1 hour. These advantages will apply for measurement of C and N in compost. Since the C/N ratio is important for compost quality, we will discuss the application of neutron gamma analysis in determining C/N ratios. This work is based on Monte-Carlo (MC) computer simulations of neutron propagation into the medium, their interaction with medium nuclei, and acquisition of gamma rays which appear due to this interaction. This method is widely used in neutron physics starting from the time of the “Manhattan Project.” Simulation software packets are currently available and we used the software toolkit “Geant4” for our simulations. MC simulations of neutron propagation in compost, and C and N gamma response from compost samples with different C/N ratios were determined. Simulations showed that the C to N gamma response ratio was directly proportional to the C/N mass ratio in samples ranging from 0-25. Results showed that compost C/N ratio can be determined by measuring C and N gamma peak areas. Measurement of C/N ratio in real compost using neutron-gamma analysis were in a good agreement with MC simulations. Economical, organizational, and radiation safety questions associated with the application of neutron gamma analysis will also be discussed. Based on our findings, the application of neutron gamma analysis for determining C/N ratio of compost is quite effective and could be used in compost fabrication.