Abstract: An earth formation traversed by a borehole is investigated. A borehole tool having a neutron source and a photon detector is located in the borehole and used to obtain photon scatter information in or about the borehole. A chemical element located in a region in or about the borehole is quantified by using the photon scatter information and at least two different spectral standards for that element.

Abstract: A method may include obtaining, using a gamma-ray detector, first acquired gamma-ray data regarding a first core sample. The first acquired gamma-ray data may correspond to various sensor steps. The method may further include determining a sensitivity map based on the first acquired gamma-ray data. The method may further include obtaining, using the gamma-ray detector, second acquired gamma-ray data regarding a second core sample at the sensor steps. The method further includes generating a gamma-ray log using the sensitivity map and a gamma-ray inversion process.

Abstract: Method for modelling a reservoir including receiving a data set relating to one or more wells within a reservoir, processing the data set to identify one or more fractures extending from the one or more wells into the reservoir, categorizing the one or more fractures as principal fractures or secondary fractures, identifying a near well high permeability region for each of the one or more wells, generating a gridded fracture plane of the one or more wells, determining a fracture permeability region, assembling the gridded fracture plane, the fracture permeability regions, and the near well high permeability region for each of the one or more wells, and generating a three-dimensional reservoir model based on the assembled gridded fracture plane for each of the plurality of predetermined depths, the fracture permeability regions, and the near well high permeability region for each of the one or more wells.

Abstract: Formation porosity is measured using a logging tool that has a pulsed neutron generator and multiple dual-function detectors that detect both neutrons and gamma rays. Ratios of thermal neutrons, epithermal neutrons, and capture gamma rays from multiple detectors are utilized to obtain multiple neutron porosities and multiple gamma-ray porosities within different depth of investigations. The neutron porosity and the gamma-ray porosity may be further corrected by excluding peak areas attributable to hydrogen and/or chlorine to reduce the shale effect and/or the chlorine effect. The neutron porosity and the gamma-ray porosity may be combined to provide improved porosity evaluations within different depth of investigations into the formation in the entire porosity measurement range (0-100 p.u.).

Abstract: A method for determining the gas pressure may include generating, via a downhole tool, neutron radiation in a cased wellbore of a geological formation and measuring a response to the neutron radiation. The method may also include determining, via a processor, at least one of a sigma, a neutron porosity, or a fast-neutron cross-section of the formation. Additionally, an equation of state of the gas may be estimated, and a gas pressure of the gas may be determined by solving a relationship, based at least in part on the equation of state, between the gas pressure and the at least one of the sigma, the neutron porosity, or the fast-neutron cross-section.

Abstract: A computer-implemented method that uses a preprogrammed neural network and a trained neural network computer program product to predict and then compared borehole and formation sigmas, when using a pulse neutron source and at least three dual-function radiation detectors. These dual-function radiation detectors are used for detecting both neutrons and gamma rays and further pre-programmed to distinguish between neutrons and gamma rays by using pulse shape discrimination techniques. The trained neural network computer program product can be used on above-surface systems, as well as below surface systems like borehole assemblies in logging-while-drilling systems.

Abstract: In some embodiments, a method includes emitting, from a transmitter positioned in a wellbore formed in a subsurface formation, a pulse of neutrons into the subsurface formation and detecting gamma ray emissions at a near field and a far field generated in response to the pulse of neutrons being emitted into the subsurface formation. The method includes determining a single elemental decay for one chemical element of a number of chemical elements present in the subsurface formation based on the gamma ray emissions and determining at least one geophysical property of the subsurface formation based on the single elemental decay of the one chemical element.

Abstract: The present disclosure is directed to methods for evaluating a gravel pack, a frac-pack, or cement in a wellbore. In at least one embodiment, a method for evaluating a gravel pack, frac-pack or cement in a wellbore, includes pumping a first material into the wellbore, wherein the first material comprises a first tracer that is not radioactive. The method includes pumping a second material into the wellbore, wherein the second material comprises a second tracer that is not radioactive. The method includes obtaining a set of data using the downhole tool in the wellbore after the first and second materials are pumped into the wellbore. The method includes obtaining a baseline using the downhole tool in the wellbore in a depth interval without the first or second material. The method includes comparing the set of data with the baseline.

Abstract: A system for non-destructive testing of an overhead energized electrical component. The system has a base, an X-ray source, an X-ray digital imager, and an imager controller. The system also has a removable electrically conductive flexible shield which is adapted to be operatively coupled to, and to encapsulate, at least the base, the X-ray source, the X-ray digital imager and the imager controller so as to form a shrouded system. In a use position, when the shrouded system is positioned adjacent the energized electrical component so as to non-destructively test the energized electrical component, the shield protects at least the base, the X-ray source, the X-ray digital imager and the imager controller from electric fields around the energized electrical component while allowing signal communication between at least the X-ray source and the energized electrical component.

Abstract: Systems and methods employed measure borehole density by neutron induced gammas using a pulsed neutron tool. Traditional nuclear density methods only measure a bulk average density of the surrounding material. As discussed below, methods to measure only the borehole density excluding the contamination from the formation are disclosed. Specifically, the proposed methods use unique signatures from each geometric region to directly measure the borehole density or compensate for the contamination from formation. This method may be achieved by a borehole density measurement using differential attenuation of capture gamma from casing iron, a borehole density measurement using differential attenuation of inelastic gamma from oxygen, a differential attenuation of any induced gamma from any element from borehole and formation, or any combination thereof.

Abstract: Fail-safe methods for deactivating the pulsed neutron generator (PNG) of a logging tool are described herein, as are logging tools configured to execute the fail-safe methods. The fail-safe methods deactivate the PNG if the logging tool is disposed in air outside of a borehole. Measurements taken using one or more gamma ray detectors of the logging tool are used to calculate a value for a parameter that is indicative of the tool being disposed in an air environment. Examples of such parameters include ratios of capture gamma rays and burst gamma rays. The disclosed methods operate without reference to sensors and/or control from outside the tool. The methods do not inadvertently deactivate the tool when it encounters an air-filled borehole.

Abstract: Gadolinium- or boron-doped drilling mud is used during drilling so that it will penetrate all natural cracks in the formation that intersect with the wellbore. Once cased, cemented and washed, the doped mud will only be in the fractures. Pulsed neutron logging is performed, and natural factures thereby characterized.

Abstract: A measurement is made of a formation containing a flood front with a downhole electromagnetic sensor. A parameter of a cross-bedding model is calculated by fitting the measurement to the cross-bedding model. A rock petrophysical parameter is calculated using the cross-bedding model. The cross-bedding model is updated using the rock petrophysical parameter. The updated cross-bedding model is used to make an operational decision.

Abstract: Methods and associated systems are disclosed for performing a logging operation within a subterranean wellbore extending within a subterranean reservoir. In an embodiment, the method includes (a) emitting neutrons into the subterranean wellbore or the subterranean reservoir, and (b) detecting gamma rays emitted from atoms disposed within the subterranean wellbore or the subterranean reservoir. In addition, the method includes (c) determining a first gamma ray count within a first energy window of the gamma rays detected at (b), and (d) determining a second gamma ray count within a second energy window of the gamma rays detected at (b). The second energy window is different than the first energy window. Further, the method includes (e) calculating a ratio of the first gamma ray count to the second gamma ray count.

Abstract: A method for determining a mineralogical composition of a geological formation sample includes measuring a mineralogical composition of the sample and measuring an elemental composition of the sample. The mineralogical composition is processed to compute a predicted elemental composition of the sample based on known elemental compositions of predetermined minerals. The measured mineralogical composition is corrected to obtain a corrected mineralogical composition which is in turn processed to compute a corresponding corrected predicted elemental composition of the sample. The measured elemental composition is compared with the predicted elemental compositions to obtain error indicators. The error indicators are compared and evaluated to selected and output one of the measured or corrected measured mineralogical compositions.

Abstract: A presence of cement may be identified based on a downhole tool that may emit neutrons into a wellbore having at least one cement casing. The neutrons may interact with the particular material via inelastic scattering, inelastic neutron reactions, capture of neutrons and/or neutron activation through one of these reactions and cause a material to emit an energy spectrum of gamma rays, and wherein the downhole tool is configured to detect an energy spectrum of the gamma rays that is specific to at least one of a plurality of elements and associated a region within the wellbore. An amount of elements, such as calcium and silicon, may be determined from the gamma ray spectra that may indicate a present of cement within the wellbore.

Abstract: A method for evaluating induced fractures in a wellbore includes obtaining a first set of data in a wellbore using a downhole tool. The method also includes pumping a first proppant into the wellbore after the first set of data is obtained. The first proppant includes a first tracer that is not radioactive. The method also includes pumping a second proppant into the wellbore. The second proppant includes a second tracer that is not radioactive. The second tracer is different than the first tracer. The first proppant and the second proppant flow into fractures in the wellbore. The method also includes obtaining a second set of data in the wellbore using the downhole tool after the first and second proppants are pumped into the wellbore. The method also includes comparing the first and second sets of data.

Abstract: Nuclear magnetic resonance methods may be used to determine the porosity and the pore type of subterranean formations while accounting for fluid infiltration from the drilling mud or mud filtrate thereof into the formation. For example, the apparent porosity of (1) a shallow sensitive volume (?sh) and (2) a deep sensitive volume (?deep) may be measured. Then, a comparison of the ?sh and the ?deep may be performed, and the porosity (?) of a portion of the subterranean formation may be calculated based on the comparison of the ?sh and the ?deep.

Abstract: Systems and methods for determining the composition of an earth formation are disclosed. One or more spectra that correspond to gamma radiation that is detected at each of multiple depths in a wellbore are generated, the contributions of each of multiple detection elements to the one or more spectra are determined, and the weight fractions of each of multiple compounds that are associated with the detection elements are calculated. The weight fraction calculations are based on a number density ratio value for the compound's associated detection element, which allows the weight fraction to be calculated directly from the contribution of the compound's associated detection element without a normalization factor.

Abstract: A method for determining a fractional volume of at least one component of a formation includes entering into a computer a number of detected radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 million electron volts (MeV). The detected radiation events correspond to at least one of an energy level of the imparted neutrons and thermal or epithermal energy neutrons. A measurement of at least one additional petrophysical parameter of the formation is made. The at least one additional petrophysical parameter measurement and at least one of a fast neutron cross-section and a thermal neutron cross-section determined from the detected radiation events are used in the computer to determine the fractional volume of the at least one component of the formation. In another embodiment, the fast neutron cross-section and the thermal neutron cross-section may be used on combination to determine the fractional volume.

Abstract: In one possible implementation, a computer-readable tangible medium includes instructions that direct a processor to access one or more wellbore properties and a plurality of well fluid properties. Instructions are also present that direct the processor to access a distance between a proposed location of an inlet to a multiphase production logging tool and an emulsion generation location in a wellbore. Further instructions instruct the processor to predict a drop size distribution of emulsified water in the well fluid at the proposed location of the inlet to the multiphase production logging tool. Additional instructions instruct the processor to compute an estimated error in water holdup detected by the multiphase production logging tool based on the drop size distribution, and recommend deployment of a pulsed neutron logging tool in the wellbore when the estimated error in the water holdup is above a preset threshold.

Abstract: An apparatus and a system, as well as methods, operable to include acquiring eddy current data from at least two concentric pipes, determining spatial frequency content of the eddy current data, and determining locations of defects in each of the pipes based on the spatial frequency content.

Abstract: A method is disclosed for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin, comprising: obtaining materials and key data; determining a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in a lithology profile and establishing a single-well lithofacies model; in the single-well lithofacies model, using a dolomite-to-formation ratio and a TOC average value to form a dolomite-to-formation ratio contour map and a TOC contour map, and superposing the dolomite-to-formation ratio contour map, the TOC contour map and a source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map; on the basis of the lithofacies plane distribution map, superposing a vitrinite reflectance contour map and a dolomite thickness contour map to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

Abstract: Systems and methods for downhole component monitoring including a monitored component doped with a pre-selected neutron absorbent, the monitored component being part of a downhole tool and a neutron monitoring system positioned relative to the monitored component. The neutron monitoring system includes a neutron source positioned at a first location relative to the monitored component and a neutron detector positioned at a second location relative to the monitored component, the neutron detector configured to detect neutrons from the neutron source and count said detected neutrons. A control unit is in communication with the neutron detector and configured to determine a status of the monitored component from the neutron count received from the neutron detector.

Abstract: A method and system for analyzing constituent elements in bulk media wherein neutrons are emitted into the bulk media to produce inelastic neutron interaction in the bulk media, and a gamma-ray spectrum resulting from the inelastic neutron interaction in the bulk media is detected. A set of standard spectra are used as part of spectral analysis that processes the standard spectra and the derived gamma-ray spectrum to determine a number of yield coefficients for the constituent elements as part of the bulk media. The standard spectra or the spectral analysis is configured to account for at least one environmental condition that affects detected gamma-rays that result from the inelastic neutron interaction in the bulk media.

Abstract: Casing condition is an important concern to oilfield operators. Systems and methods are disclosed herein for using neutron logging tools to measure casing condition, using windows in the gamma energy spectrum that are sensitive and insensitive to casing condition to obtain a ratio having a value that ranges between one extreme representative of completely absent casing and an opposite extreme representative of casing in good condition. The sensitive (“divergence”) window may be positioned at or near 7.65 MeV, the characteristic energy of gamma rays from a neutron capture event by an iron nucleus. The insensitive (“consistency”) window is preferably adjacent to the divergence window with a comparable size to the divergence window. A suitable division point between the windows may be about 6.25 MeV.

Abstract: A single volume fission energy neutron detector is described herein. The detector includes a single volume of scintillator. A photodetector is positioned adjacent to a surface of the scintillator, wherein the photodetector has relatively small spatial resolution corresponding thereto and relatively small temporal resolution corresponding thereto. Based upon values read out from detection bins of the photodetector, kinematics of a neutron that interacted with scintillating material of the scintillator are reconstructed. Based upon the kinematics (of the neutron and other detected neutrons), a location of material from which the neutron was emitted is ascertained, and an image of the material is generated.

Abstract: Various embodiments include apparatus and methods to conduct a triple phase evaluation of a formation. The evaluation can be performed using a pulsed-neutron tool including a long detector and a detector to make sigma measurements. Additional apparatus, systems, and methods are disclosed.

Abstract: A method for determining a composition of a formation, includes characterizing by energy detected gamma rays resulting from interaction of neutrons that irradiated the formation. Elemental yields are determined by spectrally analyzing the energy characterized gamma rays. A subset of the elemental yields is selected as background yields. The background yields are filtered. An apparent contribution of the filtered background yields to the characterized gamma rays is determined. Foreground elemental yields are determined by spectrally analyzing the characterized gamma rays having the apparent contribution removed.

Abstract: Systems, methods, and devices for quantitatively identifying gas zones irrespective of porosity or lithology using nuclear downhole tools are provided. In particular, because some formation materials such as shales can confound some conventional measurements, a gas detection measurement may be obtained that can be used to qualitatively identify gas zones. The gas detection measurement may be based at least partly on a relationship between inelastic gamma rays, neutron capture gamma rays, and experimental or modeled formation data, such that the gas detection measurement qualitatively indicates a gas zone when a gas zone is present in a formation irrespective of a lithology or a porosity of the formation.

Abstract: According to an embodiment, a neutron measurement apparatus has: a neutron detector; a gamma ray detector; a neutron detector signal processing unit which performs Fourier transform on the signals received for a prescribed period, generates neutron detector signal frequency data in a frequency domain, calculates the neutron-detection signal power spectrum and stores it; a gamma-ray detector signal processing unit which performs Fourier transform on the signals received for a prescribed period, generates gamma ray detector signal frequency data in a frequency domain, calculates gamma ray detector signal power spectrum and stores it; and a neutron calculation unit which generates a neutron signal by removing a part contributed by the gamma ray detector signal power spectrum from the neutron detector signal power spectrum.

Abstract: Simultaneous Multiple Sample Light Scattering systems and methods can be used for polymer stability testing and for applying stressors to polymer or colloid solutions including heat stress, ultrasound, freeze/thaw cycles, shear stress and exposure to different substances and surfaces, among others, that create a polymer stress response used to characterize the polymer solution and stability.

Abstract: An apparatus for providing a signal indicative of a property of an earth formation includes: a carrier conveyable through a borehole; a neutron source disposed on the carrier and configured to emit neutrons into the earth formation; a radiation detector disposed on the carrier and configured to detect radiation from the earth formation due to interaction of emitted neutrons with the earth formation and to provide the signal indicative of the property; and a neutron shield configured to shield the radiation detector from emitted neutrons that did not interact with the earth formation; wherein the radiation detector shield includes a glass ceramic material having a plurality of nano-crystallites, each nano-crystallite in the plurality having a periodic crystal structure with a diameter or dimension that is less than 1000 nm that includes Li and/or Boron and a rare-earth element that have positions in the periodic crystal structure of each nano-crystallite.

Abstract: Neutron activation measurement techniques may be used to evaluate various properties of a subterranean well structure. In an example implementation, a logging tool can be positioned within a wellbore, such that neutrons generated by a neutron source are directed towards well structure. In response to the neutrons, the well structure emits gamma rays. A portion of the gamma rays can be detected by a gamma detector. To enhance the well structure's response to neutron activation, the well structure can be constructed of materials that include one or more doping materials. The inclusion of these doping materials can increase the number of gamma rays that are emitted when neutrons are directed into the well structure, and these emitted gamma rays can be more easily identified based on their energy level.

Abstract: A method of generating ions in a radiation generator includes emitting electrons from an active cathode and on a trajectory away from the active cathode, at least some of the electrons as they travel interacting with an ionizable gas to produce ions. The method also includes setting a potential of at least one extractor downstream of the active cathode such that the ions are attracted toward the at least one extractor.

Abstract: Casing condition is an important concern to oilfield operators. Systems and methods are disclosed herein for using neutron logging tools to measure casing condition, using windows in the gamma energy spectrum that are sensitive and insensitive to casing condition to obtain a ratio having a value that ranges between one extreme representative of completely absent casing and an opposite extreme representative of casing in good condition. The sensitive (“divergence”) window may be positioned at or near 7.65 MeV, the characteristic energy of gamma rays from a neutron capture event by an iron nucleus. The insensitive (“consistency”) window is preferably adjacent to the divergence window with a comparable size to the divergence window. A suitable division point between the windows may be about 6.25 MeV.

Abstract: A method for determining azimuthal formation information using neutron activation, wherein the formation is activated by a neutron source and the activation signal is measured by at least one detector trailing the neutron source during the logging operation. The number of detected gamma rays as a function of the detector azimuth may be used to provide azimuthal information for determining an image of the formation surrounding the borehole.

Abstract: Methods for determining a value indicative of liquid density of a formation include obtaining an inelastic count rate and a capture count rate of a gamma detector for a particular borehole depth, calculating a ratio of an inelastic count rate to a capture count rate for the particular borehole depth, determining a value indicative of liquid density based on the ratio of the inelastic count rate to the capture count rate for the particular borehole depth, repeating the obtaining, calculating and determining for a plurality of borehole depths, and producing a plot of the value indicative of liquid density of the formation as a function of borehole depth.

Abstract: Methods and related systems are described for gamma-ray detection. A gamma-ray detector is made depending on its properties and how those properties are affected by the data analysis. Desirable properties for a downhole detector include; high temperature operation, reliable/robust packaging, good resolution, high countrate capability, high density, high Z, low radioactive background, low neutron cross-section, high light output, single decay time, efficiency, linearity, size availability, etc. Since no single detector has the optimum of all these properties, a downhole tool design preferably picks the best combination of these in existing detectors, which will optimize the performance of the measurement in the required environment and live with the remaining non-optimum properties.

Abstract: Systems and methods for measuring neutron-induced activation gamma-rays in a subterranean formation are provided. In one example, a downhole tool for measuring neutron-induced activation gamma-rays may include a neutron source and a gamma-ray detector. The neutron source may emit neutrons according to a pulsing scheme that includes a delay between two pulses. The delay may be sufficient to allow substantially all neutron capture events due to the emitted neutrons to cease. The gamma-ray detector may be configured to detect activation gamma-rays produced when elements activated by the emitted neutrons decay to a non-radioactive state.

Abstract: A method of evaluating a cased borehole in an earth formation includes: emitting at least one acoustic signal into the borehole via an acoustic source and detecting a return acoustic signal via an acoustic sensor, the borehole including a casing and a casing support material disposed between the casing and a borehole wall; emitting a neutron flux via a neutron source into the borehole and detecting a radiation signal via a radiation detector, the radiation signal including induced gamma radiation resulting from neutron interactions; and identifying a casing support material characteristic based on the return acoustic signal and the radiation signal.

Abstract: A method for estimating an aspect of a formation using a nuclear spectroscopy tool includes placing a nuclear spectroscopy tool including a neutron source and a gamma ray detector into a borehole and performing a plurality of environmental measurements. Neutrons are emitted from the nuclear spectroscopy tool such that some of the neutrons generate gamma rays from a formation adjacent the nuclear spectroscopy tool, some of the neutrons generate gamma rays from elements within the nuclear spectroscopy tool and some of the neutrons generate gamma rays from an element in the drilling mud. An energy spectrum of gamma rays induced by the emitted neutrons can be detected with the tool and analyzed using a combination of standard spectra including at least two sub-standards that represent a common element or group of elements and that are differentiated based on location of neutron interaction, such as where the neutrons thermalize.

Abstract: Method and apparatus for evaluating an earth formation using at least one detector with a pulsed neutron source that includes a beam of deuterium ions that can be directed to a selected position on a target including tritium that extends axially along a sealed tube. This makes it possible to generate pulsed neutrons from a plurality of positions.

Abstract: Methods and systems to determine and regulate the gain of gamma-ray detectors in tools equipped with neutron sources are provided. Gain regulation may be based on the gamma ray background generated in the tool by interaction of neutrons with the nuclei of some elements constituting the tool structure. Some chemical elements that are used in construction of the tool's mechanical parts and structure result in characteristic gamma ray lines in a measured energy spectrum. These lines can be used to calibrate the energy scale of the response of the detector, without any added calibration radio isotopic source.

Abstract: A method of formation evaluation using a pulsed neutron tool. The approach removes the effect of formation hydrogen index (HI) from the nuclear response of the tool. It can be used for gas detection and quantification, as well as for other fluids. It can also be used to improve a formation hydrogen index (HI) measurement.

Abstract: Determining a value indicative of fracture quality. At least some of the illustrative embodiments are methods including: obtaining or measuring gas saturation of a formation to create a value indicative of pre-fracture gas saturation; and after a fracturing process measuring gas saturation of the formation to create a value indicative of post-fracture gas saturation; and creating a value indicative of fracture quality based on the value indicative of pre-fracture gas saturation and the value indicative of post-fracture gas saturation.

Abstract: A method of generating ions in a radiation generator includes emitting electrons from an active cathode and on a trajectory away from the active cathode, at least some of the electrons as they travel interacting with an ionizable gas to produce ions. The method also includes setting a potential of at least one extractor downstream of the active cathode such that the ions are attracted toward the at least one extractor.

Abstract: A method for estimating an aspect of a formation using a nuclear spectroscopy tool includes placing a nuclear spectroscopy tool including a neutron source and a gamma ray detector into a borehole and performing a plurality of environmental measurements. Neutrons are emitted from the nuclear spectroscopy tool such that some of the neutrons generate gamma rays from a formation adjacent the nuclear spectroscopy tool, some of the neutrons generate gamma rays from elements within the nuclear spectroscopy tool and some of the neutrons generate gamma rays from an element in the drilling mud. An energy spectrum of gamma rays induced by the emitted neutrons can be detected with the tool and analyzed using a combination of standard spectra including at least two sub-standards that represent a common element or group of elements and that are differentiated based on location of neutron interaction, such as where the neutrons thermalize.

Abstract: Determining a value indicative of fracture quality. At least some of the illustrative embodiments are methods including: obtaining or measuring gas saturation of a formation to create a value indicative of pre-fracture gas saturation; and after a fracturing process measuring gas saturation of the formation to create a value indicative of post-fracture gas saturation; and creating a value indicative of fracture quality based on the value indicative of pre-fracture gas saturation and the value indicative of post-fracture gas saturation.

Abstract: A method for estimating an aspect of a formation using a nuclear spectroscopy tool includes placing a nuclear spectroscopy tool into a borehole and emitting neutrons such that some of the neutrons generate gamma rays from a formation adjacent the nuclear spectroscopy tool and some of the neutrons generate gamma rays from elements within the nuclear spectroscopy tool. An energy spectrum of gamma rays induced by the emitted neutrons can be detected. The energy spectrum includes a background having a plurality of measured spectral components. A background ratio between at least one spectral component of the background and another measured spectral component can be determined or estimated in accordance with environmental measurements. The detected gamma ray spectra can be analyzed using a combination of standard spectra and subtracting at least one spectral component of the background in accordance with the background ratio.