System and method of using energy correlated timing spectra to locate subsurface objects

Inventors

Torbert, III, Henry A.Prior, Stephen A.KAVETSKIY, ALEKSANDRYAKUBOVA, GALINA N.

Assignees

US Department of Agriculture USDA

Publication Number

US-11402338-B2

Publication Date

2022-08-02

Expiration Date

2039-09-05

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Abstract

Multiple tagged neutrons are emitted from an associated particle imaging neutron generator. The tagged neutrons penetrate a target material and interact with the target material nucleus—which emits nucleus-specific gamma rays. A gamma ray detector detects all gamma rays—including the nucleus-specific gamma rays. An alpha-gamma timing spectrum is constructed for all detected gamma rays. For a specific energy level (MeV) corresponding with the target material nucleus, a peak in the alpha gamma timing spectrum indicates the presence of the target material. Based on the peaking time of the gamma rays (due to tagged neutrons interaction with the target material nucleus) in the alpha-gamma timing spectrum for the specific energy level, the distance from the neutron generator to the target material can be calculated. The nucleus-specific gamma ray spectrum data can be effectively collimated by programming the system to detect the gamma rays in a time window corresponding to the peaking time.

Core Innovation

The invention provides a non-destructive method and a portable device for identifying buried target materials by using an Associated Particle Imaging (API) system that emits tagged neutrons and detects coincident alpha particles. The tagged neutrons penetrate target materials and interact with their nuclei, which emit nucleus-specific gamma rays. By detecting these gamma rays and constructing an alpha-gamma timing spectrum at specific gamma energy levels corresponding to the target material nucleus, the presence of the material is indicated by spectral peaks.

The system resolves the problem of locating subsurface objects non-invasively and with specificity by correlating the time of gamma ray peaks in the alpha-gamma timing spectrum to the distance from the neutron generator to the target material. The method employs energy-correlated timing spectra and time-correlated gamma energy spectra to precisely determine the location and elemental content in an investigated area, overcoming limitations in target neutron techniques for identifying hidden materials beneath surfaces.

The problem addressed includes difficulties in locating and identifying buried or subsurface objects such as carbon bricks or other elemental compositions with sufficient signal-to-noise ratio and depth resolution. Existing API setups could measure alpha-gamma coincidence timing spectra but lacked the refined method of correlating energy and timing spectra to deduce distances to specific buried targets. The invention enables the electronic collimation of neutron beams via timing windows, improving detection accuracy and enabling depth localization without mechanical collimation.

Claims Coverage

The patent claims cover a nondestructive method of identifying buried materials utilizing a field-portable API device. The independent claims highlight the use of tagged neutron and alpha particle emissions, detection of nucleus-specific gamma rays, timing spectra construction, and calculations of distance to buried targets without complex imaging systems.

Using a field-portable API device for non-invasive elemental measurements

The method uses a field-portable device comprising a neutron generator with an Associated Particle Imaging system alpha detector to perform non-invasive measurements of elemental content in buried materials.

Emitting tagged neutrons and alpha particles and detecting coincident events

Multiple tagged neutrons and corresponding tagged alpha particles are emitted simultaneously, where tagged alpha particle detection allows determination of the neutron emission time, trajectory, and enables tagging the neutron interactions with target nuclei that release nucleus-specific gamma rays.

Constructing and analyzing alpha-gamma event time distribution spectra

An alpha-gamma event time distribution is recorded and examined for spectral peaks corresponding to nucleus-specific gamma rays. The time difference between neutron emission and gamma detection is used to infer the distance to the target buried material.

Determining the distance to buried materials without Compton cameras or 3D imaging

The distance from the neutron source to the buried target material is determined based on measured times and known neutron and gamma speeds, accomplishing target localization without employing Compton cameras or electronic circuits designed for three-dimensional imaging.

Energy-correlated timing spectra used to collimate and identify buried materials

Time correlated energy spectra are utilized within specific time increments to electronically collimate data, enhancing depth localization and allowing comparison against known reference spectra to determine elemental content in the investigated buried material.

Overall, the independent claims are centered on a method using a portable neutron generator API system that emits tagged neutron-alpha pairs, detects nucleus-specific gamma rays with alpha-gamma timing spectra, and calculates distances to buried objects by analyzing time-energy correlated spectra, enabling improved depth localization and elemental identification without complex imaging hardware.

Stated Advantages

Provides higher signal-to-noise ratio compared to other neutron-gamma analysis methods due to operating in alpha-gamma coincidence mode.

Enables non-invasive, in situ measurements of elemental content and precise localization of buried materials such as carbon bricks.

Allows accurate determination of distance to buried objects using timing spectra without needing mechanical collimation or complex imaging devices.

Improves the minimum detectable level (MDL) of carbon detection by more than 2 times compared to continuous mode measurements.

Offers electronic collimation of neutron beams through programmable timing windows, enhancing measurement specificity and sensitivity.

Documented Applications

Locating subsurface objects such as discrete carbon masses, plant roots, root crops, and similar buried target materials.

Non-invasive soil carbon analysis within a conical investigated volume defined by the API system.

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