Methods and systems for non-invasive measurement of soil chlorine and/or nitrogen content and for detecting sub-surface chlorine or nitrogen-containing objects
Inventors
Torbert, III, Henry A. • Prior, Stephen A. • KAVETSKIY, ALEKSANDR G. • YAKUBOVA, GALINA N.
Assignees
US Department of Agriculture USDA
Publication Number
US-10753891-B2
Publication Date
2020-08-25
Expiration Date
2037-04-24
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Abstract
The presence of chlorine and nitrogen are determined and measured using a non-invasive portable neutron-generating and gamma ray detecting system(s). Portable devices of the present invention can also be used to detect chlorine and/or nitrogen-containing underground objects rapidly and on-site. Devices and systems described herein can be operated remotely and pre-programmed with search patterns, guided by an operator remotely, or programmed to home in on high-chlorine and/or nitrogen concentration areas.
Core Innovation
The invention provides methods and systems for the non-invasive measurement of soil chlorine and nitrogen content and for detecting chlorine or nitrogen-containing objects beneath the soil surface using a portable neutron-generating and gamma ray detecting system. The system utilizes a pulsed neutron generator and gamma ray detector to measure gamma ray emissions induced by neutron irradiation, enabling rapid on-site detection and quantification of chlorine and nitrogen without disturbing the soil or object.
The underlying problem addressed is the difficulty and expense associated with traditional soil chlorine detection methods, which require invasive soil sampling, laboratory chemical analyses, and extensive sample handling to prevent contamination. Chlorinated hydrocarbons, which contaminate soils through various routes and pose environmental hazards and toxic risks, are currently challenging to detect and quantify quickly and remotely. Similarly, nitrogen content measurement for agronomic use and explosive detection is presently costly and time-consuming. This invention addresses the need for a fast, remote, and non-destructive detection method and apparatus for such elemental detection in soils and buried objects.
Claims Coverage
The patent contains a set of independent claims focused on a detection system for nitrogen on or below a testable surface and associated methods for determining nitrogen presence and carbon to nitrogen ratios.
Detection system structured to utilize pulsed neutron beams with separated gamma spectra acquisition
The system comprises a neutron generator assembly producing pulsed neutron beams, a moderator positioned between the neutron generator and testable surface, and a gamma ray detector to detect gamma rays from materials at or below the surface. It includes a gamma ray detector processor/controller with a split electronics processing system that separates gamma spectra acquired during neutron pulses from that acquired between pulses, particularly collecting thermal neutron capture (TNC) gamma spectra between pulses without consideration of resonant neutron time of flight.
Thermal neutron capture gamma spectra indicating nitrogen presence using characteristic gamma peaks
The presence of nitrogen is indicated when the TNC gamma ray spectra data shows multiple count rate peaks centered around 9.2-11.6 MeV, with quantification based on total area fitted by three Gaussian peaks with centroids at approximately 10.82 MeV, 10.32 MeV (single escape peak), and 9.82 MeV (double escape peak). The total area of these peaks is directly proportional to the nitrogen weight percent in the materials.
Method for noninvasive determination of carbon to nitrogen ratio using gamma spectra
A method involving use of the above detection system to determine nitrogen presence, obtaining soil carbon content by evaluating a 4.43 MeV peak in inelastic neutron scattering (INS) spectra acquired during neutron pulses, and then calculating the carbon to nitrogen ratio of the testable materials.
Modular system construction featuring deuterium-tritium neutron generator, polyethylene moderator, and sodium iodide gamma detector
The neutron generator assembly includes an accelerator tube and controller and is implemented as a deuterium-tritium (D-T) generator producing approximately 14 MeV neutron beams. The moderator is a polyethylene substrate between four to six centimeters thick. The gamma ray detector is comprised of sodium iodide (NaI(Tl)) with a volume of at least 2.4 dm3. Gamma ray shielding, including lead, is positioned between the neutron generator and gamma detector. The system includes a monitoring/controlling computer system, typically a laptop, to communicate with and control system components. The whole system is portable and suitable for soil testing.
The independent claims articulate an inventive portable detection system employing pulsed neutrons, moderated thermal neutrons, and split electronics to acquire and process gamma ray spectra for non-invasive nitrogen detection, quantification, and carbon to nitrogen ratio determination, with defined hardware components and operational methods.
Stated Advantages
Enables non-invasive, rapid, and on-site detection and quantification of chlorine and nitrogen in soils and buried objects without the need for invasive sampling and laboratory analysis.
Allows remote operation and automated or guided scanning over multiple locations, improving spatial contamination assessment efficiency.
Provides simultaneous measurement of nitrogen and chlorine using separate gamma spectra acquisition during and between neutron pulses, enhancing signal-to-background separation and detection sensitivity.
Portable and adaptable system including components such as a pulsed neutron generator, moderator, gamma detector, and shielding, facilitating field deployment.
Capability to detect buried objects containing chlorine or nitrogen to depths of several centimeters to several dozen centimeters, expanding usability in environmental monitoring and explosive detection.
Documented Applications
Rapid on-site measurement and detection of soil surface chlorine contamination resulting from environmental pollution or industrial processes.
Detection and localization of buried chlorine-containing objects such as explosive ordnance or chemical contaminants in soils.
Measurement of soil nitrogen content and determination of carbon to nitrogen ratios relevant to agricultural applications such as manure application rates and compost quality control.
Identification and monitoring of nitrogen-containing substances for remediation of contaminated soils and detection of buried explosives, particularly on military training ranges.
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