Abstract: A well logging tool includes a neutron generator having an ion source cathode comprising a nano-structure field emission (FE) array for producing a charged particle current routed through an ionizable gas, thus generating ions by electron impact ionization of the gas. The nanostructures can be provided by bundles of silicon nanotips grown on a substrate. The FE array can be provided on an axially facing substrate located co-axially in an elongate housing, with the charged particle current directed from the centrally located FE array to a co-axial annular anode and having axial and radial directional components.

Abstract: A tool can include an X-ray tomography device to evaluate cement in a downhole environment. The X-ray tomography device includes an X-ray beam source configured to transmit an X-ray beam at a first predetermined angle. The beam angle may be set by a capillary device coupled to the X-ray beam source. An energy dispersive, multi-pixel photon detector is configured to count detected backscatter photons received at a second predetermined angle and determine an energy spectrum for the detected photons. A density map of the cement may be generated in response to the number of detected photons. Additional apparatus, systems, and methods are disclosed.

Abstract: A downhole tool can include a photon beam source configured to transmit a photon beam into materials lining a wellbore. The materials may comprise fluid, casing, and cement. A photon detector in the tool is configured to count detected photons received at a predetermined angle from the materials. The density of the borehole material may be determined in response to the number of detected photons. Changes in a distribution of a plurality of photon count ratio values may indicate the standoff distance. Additional apparatus, systems, and methods are disclosed.

Abstract: A gamma-ray spectrometer calibration system comprises a photomultiplier tube and analysis electronics. The photomultiplier tube provides one or more reference signals that are analyzed relative to a spectrum by the analysis electronics to calibrate a gamma-ray spectrometer. Additional apparatus, methods, and systems are disclosed.

Abstract: Methods, systems, and computer program products for identifying annular space materials calculate a near-to-far (“N/F”) neutron count ratio from neutron count rates detected by detectors located near to and far from a neutron source, respectively. The N/F neutron count ratio may then be used along with formation porosity to provide an estimation of the type of material that may be present in the annular space.

Abstract: A neutron generator includes a gas control interface and a vacuum chamber coupled to the gas control interface. The neutron generator also includes a target rod disposed within the vacuum chamber and having a longitudinal axis aligned with a central axis of the vacuum chamber, and further including a target disposed on a surface of the target rod facing the getter. The neutron generator also includes a planar ion source adjacent to the gas control interface and disposed between the target and the gas control interface. The planar ion source includes an array grid that is offset from the target and generally perpendicular to the longitudinal axis of the target rod.

Abstract: A neutron generator includes a gas control interface and a vacuum chamber coupled to the gas control interface. The neutron generator also includes a target rod disposed within the vacuum chamber and having a longitudinal axis aligned with a central axis of the vacuum chamber, and further including a target disposed on a surface of the target rod facing the getter. The neutron generator also includes a planar ion source adjacent to the gas control interface and disposed between the target and the gas control interface. The planar ion source includes an array grid that is offset from the target and generally perpendicular to the longitudinal axis of the target rod.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive photons at inner surfaces of an array of tubes forming a columnar structure, the tubes including a material with substantially high density, wherein longitudinal axes of the tubes are substantially parallel. Further activities include directing the photons within the columnar structure to a position-sensitive detector to measure the photons, wherein the position-sensitive detector is divided into an array of pixels, and wherein individual ones of the tubes in the array of tubes maintain a fixed mechanical arrangement with individual ones of the array of pixels, to provide collimation of the photons from a first end of the tubes to a second end of the tubes coupled to the position-sensitive detector. Additional apparatus, systems, and methods are described.

Abstract: Various apparatus or methods are arranged to operate a tool downhole in a well, where the tool has a detection package operable to detect gamma rays. Spectra peaks of the detected gamma rays can be determined in each of selected energy windows. Distribution of radiation tracer can be determined in one or more regions around the tool from ratios of the spectra peaks. Additional apparatus, systems, and methods having a gamma ray detection package can operate in a variety of applications.

Abstract: In some embodiments, an apparatus and a system, as well as a method, may operate to transform photons received at a scintillator into scintillation energy at a light yield efficiency of at least 30% at temperatures above 150 C. Further activities may include converting the scintillation energy to electron-hole pairs within a pixelated array of a position-sensitive detector having a bandgap of at least 2 eV. Additional apparatus, systems, and methods are described.

Abstract: The disclosed embodiments include downhole gamma-ray generators and methods to utilize downhole gamma-ray generators in a downhole environment. In one embodiment, a downhole gamma-ray generator includes a target foil formed from a first material. The downhole gamma-ray generator also includes a second layer deposited along a back surface of the target foil. The downhole gamma-ray generator further includes a laser system operable to direct optical pulses onto a front surface of the target foil to ionize atoms of the first material, where electrons produced by ionization of the first material propagate through the target foil and decelerates when the electrons interact with the high density material, and where the deceleration of the electrons produces gamma-rays that are utilized to obtain one or more formation properties of a downhole formation.

Abstract: A neutron detection apparatus, method, and system includes a scintillation device that emits photons in response to received neutron energy incident on the device. A gamma radiation source, coupled to the scintillation device and configured to emit a reference energy, is also detected by the scintillation device. The reference energy has a different energy than the neutron radiation. A light sensor is coupled to the scintillation device. The light sensor receives and converts the emitted photons into an electrical signal comprising an indication of both the reference energy and the received neutron energy.

Abstract: A tomographic imaging apparatus utilizes Compton backscattering to evaluate cement behind the casing. The imaging apparatus includes a slant-hole or pin-hole collimator coupled to a series of detectors in order to count the number of photons that backscatter off from the cement. The number of backscattered photons is proportional to the density of the cement behind the casing. Using the photon count, an image processing unit of the imaging apparatus generates a 2D or 3D tomographic image of the borehole.

Abstract: A system and method to determine a characteristic of a wellbore based on count rates of scattered photons. The system and method can include determining at least one characteristic of a material surrounding a wellbore by, emitting photons from a photon source at a location in the wellbore, detecting, via one or more detectors, photons scattered by the material, counting the scattered photons based on an energy level, producing count rates of the detected photons for various energy ranges, and calculating a value of the characteristic based on the count rates. The material can be at least one of mud, mud cake, and earth formation.

Abstract: In some embodiments, an apparatus, system, and method may operate to determine the density of drilling fluid associated with photon activity in the drilling fluid using an array of nuclear detectors. Further activity may include determining acoustic impedance of the drilling fluid as a combination of the density and acoustic velocity. Additional apparatus and systems, as well as methods, are disclosed.

Abstract: A method for cement evaluation may include generating a gamma ray, from a radioactive source, into cement disposed between a casing and a geological formation. Photons reflected from the geological formation and the cement are detected on a gamma detector having a collimator. A detector-to-source distance, a collimator angle, and/or a collimator diameter are set to provide an energy spectra independent of the geological formation. The quality of the cement may be determined based on the energy spectra of the detected photons.

Abstract: A laser photopeak location system comprises a gamma-ray spectrometer and a processor. The processor computes a plurality of correlation coefficients based on a comparison of a pulse-height spectrum of the gamma-ray spectrometer with an array of values. The processor locates one or more photopeaks of the pulse-height spectrum based on at least one of the plurality of correlation coefficients. Additional apparatus, methods, and systems are disclosed.

Abstract: In some embodiments, a method and apparatus, as well as an article, may operate to estimate a property of an earth formation by generating at least one shale model to represent an earth formation comprised of a non-zero percentage of shale. The shale model includes two curves to represent a relationship between a porosity parameter and a pulsed neutron measurement at two different corresponding percentages of gas saturation, respectively. A matrix model representing an earth formation with 0% shale is combined with one or more shale models to create a formation model. Measured pulsed neutron data is compared with the formation model to estimate a property of the earth formation. Additional apparatus, systems, and methods are disclosed.

Abstract: Various embodiments include apparatus and methods of using the apparatus having a neutron generator. The neutron generator can include a neutron generator tube having a cylindrical inner surface that bounds a cylindrical cavity, a field ionization array cylindrically distributed on the cylindrical inner surface, and a target rod positioned in the cylindrical cavity. Additional apparatus, systems, and methods are disclosed.

Abstract: Evaluation of borehole annulus cement quality is performed by an artificial neural network configured to estimate one or more cement attributes based on a radiation response of the annulus cement. A plurality of attributes indicative of quality of cement in the annulus can be estimated or derived based on gamma radiation response information (such as a gamma spectrum of the annulus cement). The artificial neural network is trained to perform the estimation by provision to the artificial neural network of training data from multiple example boreholes. The training data can include empirical data and/or simulation data.