Abstract: A downhole tool operable for conveyance within a wellbore extending into a subterranean formation, and for obtaining one or more measurements of the subterranean formation, wherein the downhole tool comprises a sensor, a pressure housing containing the sensor and mounted on an external surface of the downhole tool, and a sliding stabilizer covering the pressure housing.

Abstract: A method for evaluating wellbore conduit condition includes using measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission. The at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts are characterized to estimate an amount of loss of iron in the conduit.

Abstract: Methods and systems for determining whether a tool has been deployed below a drill pipe are provided. A downhole tool can measure various characteristics, which then can be analyzed to determine the likelihood of a tool having been deployed below the drill pipe. For example, density and porosity measurements can be affected by the presence of casing or drill pipe, and thus such measurements can provide an indication of whether the tool has been deployed below the drill pipe.

Abstract: A method for improving precision of measurement of material composition of formations determined by gamma ray spectral an analysis includes determining an accurate value of an amount of a selected by analyzing a spectrum of gamma rays detected from the formations using a technique that directly relates the gamma ray spectrum to the amount of the material. A precise value of the amount of the material is determined by analyzing the spectrum of detected gamma rays that indirectly relates the gamma ray spectrum to the amount of the material. A function relating the accurate value to the precise value over a selected axial interval along the wellbore is determined. The function is applied to the accurate value at at least one selected axial position along the wellbore to determine an accurate and precise value of the amount of the material.

Abstract: Systems, methods, and devices with improved electrode configuration for downhole nuclear radiation generators are provided. For example, one embodiment of a nuclear radiation generator capable of downhole operation may include a charged particle source, a target material, and an acceleration column between the charged particle source and the target material. The acceleration column may include several electrodes shaped such that substantially no electrode material from the electrodes is sputtered onto an insulator surface of the acceleration column during normal downhole operation.

Abstract: A method for determining a petrophysical property of a formation includes detecting radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 MeV. The petrophysical property is determined from an elastic scattering cross section of the formation. The elastic scattering cross-section related to a number of detected radiation events.

Abstract: A method for determining a formation thermal neutron decay rate from measurements of radiation resulting from at least one burst of high energy neutrons into formations surrounding a wellbore includes determining a first apparent neutron decay rate in a time window beginning at a first selected time after an end of the at least one burst, a second apparent decay rate from a time window beginning at a second selected time after the burst and a third apparent decay rate from a third selected time after the burst. The second time is later than the first time. A thermal neutron capture cross section of fluid in the wellbore is determined. A decay rate correction factor is determined based on the first and second apparent decay rates and a parameter indicative of the wellbore capture cross-section. The correction factor is applied to the third apparent decay rate to determine the formation thermal neutron decay rate.

Abstract: A radiation detector is used in a well-logging tool for positioning in a wellbore of a geologic formation. The radiation detector includes a photomultiplier housing and a scintillator housing. A housing coupler joins together opposing ends of the photomultiplier housing and scintillator housing. A photomultiplier is contained within the photomultiplier housing and a scintillator body is contained within the scintillator housing. A scintillator window is secured to the housing coupler.

Abstract: Systems, methods, and devices for thermally protecting a scintillator crystal of a scintillation detector are provided. In one example, a thermally-protected scintillator may include a scintillator crystal and a thermal protection element, which may partially surround the scintillator crystal. The thermal protection element may be configured to prevent the scintillator crystal from experiencing a rate of change in temperature sufficient to cause cracking or non-uniform light output, or a combination thereof.

Abstract: Composition-matched downhole tools and methods for using such tools are provided. One such method includes emitting neutrons using a neutron source in the downhole tool to generate formation gamma rays in a surrounding formation. At the same time, however, some of the neutrons may interact with different parts of the downhole tool to form tool gamma rays. The gamma ray spectra of at least some of the formation gamma rays and the tool gamma rays may be detected using a gamma ray detector. The tool gamma rays from the different parts of the tool may have a substantially similar spectral shape. As such, a processor may be used to analyze the spectra of the tool gamma rays using a single tool background standard, thereby simplifying the analysis and improving the precision of the results.

Abstract: A method is described for obtaining an accurate and precise value for radiation output of a radiation generator. Radiation is generated in the radiation generator, and the radiation output of the radiation generator is measured using a radiation monitoring device. An instantaneous inferred radiation output is determined from operating parameters of the radiation generator, and over a period of time a calibration factor between the measured and the instantaneous inferred radiation output is determined. The accurate and precise value for radiation output is determined from the instantaneous inferred radiation output and the determined calibration factor.

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 is described for obtaining an accurate and precise value for radiation output of a radiation generator. Radiation is generated in the radiation generator, and the radiation output of the radiation generator is measured using a radiation monitoring device. An instantaneous inferred radiation output is determined from operating parameters of the radiation generator, and over a period of time a calibration factor between the measured and the instantaneous inferred radiation output is determined. The accurate and precise value for radiation output is determined from the instantaneous inferred radiation output and the determined calibration factor.

Abstract: A well-logging device may include a housing to be positioned within a borehole of a subterranean formation, and at least one radiation source carried by the housing to direct radiation into the subterranean formation. The well-logging device may also include noble gas-based radiation detectors carried by the housing in azimuthally spaced relation to detect radiation from the subterranean formation. A controller may determine at least one property of the subterranean formation based upon the detected radiation from the noble gas-based radiation detectors.

Abstract: A method is for creating a gamma ray source downhole by creating a radioactive material through irradiation of an inert material by high energy neutrons, wherein the material to be activated may surround the neutron source in close proximity to form a compact gamma ray source. The gamma rays generated by the activation may be used to perform nuclear measurements downhole.

Abstract: Method and system for analyzing electrical pulses contained in a pulse train signal representative of the interaction of x-ray bursts with a nuclear detector configured for subsurface disposal. The pulse train signal is sampled to form a digitized signal. The total energy deposited at the detector during an x-ray burst is determined from the digitized signal, and a count rate of x-ray pulses from the burst is determined. A subsurface parameter is determined using the total energy deposit.

Abstract: A radiation detector is used in a well-logging tool for positioning in a wellbore of a geologic formation. The radiation detector includes a photomultiplier housing and a scintillator housing. A housing coupler joins together opposing ends of the photomultiplier housing and scintillator housing. A photomultiplier is contained within the photomultiplier housing and a scintillator body is contained within the scintillator housing. A scintillator window is secured to the housing coupler.

Abstract: Methods for pre-treating packaging materials of particular composition for use in conjunction with a scintillation crystal are disclosed. The packaging materials may comprise a reflecting material, an elastomer, a reflecting fluorocarbon polymer, a polymer or elastomer loaded with a reflecting inorganic powder (including a reflecting inorganic powder comprising a high reflectance material selected from the group comprising Al2O3, TiO2, BN, MgO, BaSO4 and mixtures thereof), or a highly reflective metal foil selected from the group comprising Ag and Al that is chemically compatible with the scintillator crystal. The scintillator crystal may comprise a crystal selected from the group comprising NaI(Tl), LaBr3:Ce, La—Cl3:Ce, La-halides, and La-mixed halides.

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: Systems, methods, and devices for thermally protecting a scintillator crystal of a scintillation detector are provided. In one example, a thermally-protected scintillator may include a scintillator crystal and a thermal protection element, which may partially surround the scintillator crystal. The thermal protection element may be configured to prevent the scintillator crystal from experiencing a rate of change in temperature sufficient to cause cracking or non-uniform light output, or a combination thereof.