Abstract: A downhole tool includes a radiation generator configured to output radiation using electrical power received from a power supply. A first portion of the radiation is emitted into a surrounding sub-surface formation. The downhole tool also includes a radiation detector coupled proximate the radiation generator. The radiation detector includes a micromesh gaseous detector, and the radiation detector is configured to output a measurement signal based at least in part on interaction between a second portion of the radiation output by the radiation generator and the radiation detector. Additionally, the downhole tool includes a control system communicatively coupled to the radiation generator and the radiation detector. The control system is configured to determine measured characteristics of the radiation output from the radiation generator based at least in part on the measurement signal and to control operation of the radiation generator based at least in part on the measured characteristics.

Abstract: A system for a downhole tool includes an X-ray generator that outputs X-ray radiation into a surrounding sub-surface formation using electrical power received from a power supply and a detector device adjacent the X-ray generator. The detector device includes a first detector with a first radiation sensitivity that outputs a first measurement signal based on interaction between a first portion of the X-ray radiation and the first detector. The detector device also includes a second detector with a second radiation sensitivity adjacent the first detector, where the second detector outputs a second measurement signal based on interaction between a second portion of the X-ray radiation and the second detector.

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 is 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: Disclosed is a radiation logging tool, comprising a tool housing; a compact generator that produces radiation; a power supply coupled to the compact generator; and control circuitry. Embodiments of the compact generator comprise a generator vacuum tube comprising a source generating charged particles, and a target onto which the charged particles are directed; and a high voltage supply comprising a high voltage multiplier ladder located laterally adjacent to the generator vacuum tube. The high voltage supply applies a high voltage between the source and the target to accelerate the charged particles to a predetermined energy level. The compact generator also includes an electrical coupling between an output of the high voltage supply and the target of the generator vacuum tube to accommodate the collocated positions of the generator vacuum tube and the high voltage power supply.

Abstract: A well-logging tool may include a sonde housing, and a radiation generator carried by the sonde housing. The radiation generator may include a generator housing, a target carried by the generator housing, a charged particle source carried by the generator housing to direct charged particles at the target, and at least one voltage source coupled to the charged particle source. The at least one voltage source may include a voltage ladder comprising a plurality of voltage multiplication stages coupled in a bi-polar configuration, and at least one loading coil coupled at at least one intermediate position along the voltage ladder. The well-logging tool may further include at least one radiation detector carried by the sonde housing.

Abstract: Systems, methods, and devices for inelastic gamma-ray logging are provided. In one embodiment, such a method includes emitting neutrons into a subterranean formation from a downhole tool to produce inelastic gamma-rays, detecting a portion of the inelastic gamma-rays that scatter back to the downhole tool to obtain an inelastic gamma-ray signal, and determining a property of the subterranean formation based at least in part on the inelastic gamma-ray signal. The inelastic gamma-ray signal may be substantially free of epithermal and thermal neutron capture background.

Abstract: Methods and downhole tools involving neutron-absorbing gamma ray windows are provided. One such method involves emitting neutrons from a neutron source in a downhole tool in a well into a surrounding geological formation. This may produce formation gamma rays through interactions between the neutrons and elements of the geological formation. The formation gamma rays may be detected by a gamma ray detector when the gamma rays pass via a gamma ray window that includes a neutron-absorbing material disposed in a substrate material of the downhole tool. The gamma ray window may be both more transmissive of gamma rays than the substrate material and less transmissive of neutrons than a window without the neutron-absorbing material. This may decrease a neutron flux that would otherwise reach the gamma ray detector and the tool materials surrounding it and thus would otherwise lead to a background signal contaminating a signal corresponding to the detected formation gamma rays.

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 scintillator type radiation detector package is provided including a scintillation crystal directly coupled to the window of a photomultiplier. A scintillator package is also provided having a longer life at wellbore temperature with minimal deterioration of a hygroscopic scintillation crystal(s). Direct optical coupling of the scintillator to the photomultiplier reduces the amount of light lost at coupling interfaces and improved detection resolution over the conventional structures having separate packages for crystal and photomultiplier.

Abstract: The current disclosure is related to a downhole tool that comprises an electronic photon generator and at least one detector. The electronic photon generator comprises a cathode configured to emit electrons, a first target configured to generate photons when struck by the electrons, a second target configured to generate photons when struck by the electrons, and a beam steering device that directs the electrons to a first or second target. The at least one detector is configured to detect at least some of the photons emitted by the first target and at least some of the photons emitted by the second target.

Abstract: The disclosure relates to a method for correcting a downhole natural gamma-ray measurement performed in a wellbore. A gamma-ray measurement including at least a gamma-ray count rate is obtained by a gamma-ray detector disposed in a bottom hole assembly having a mud channel inside of the assembly, such that mud flows downwards in the mud channel and upwards outside of the assembly and a neutron source situated above the gamma-ray detector and activating the mud.

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: A method for estimating a drilling fluid flow rate in a subterranean wellbore includes processing an acquired gamma ray spectrum in combination with standard elemental spectra and at least one standard oxygen activation spectrum to compute an oxygen activation yield. The oxygen activation yield is further processed to estimate a drilling fluid flow rate and or to infer a borehole diameter change or a lost circulation event. The gamma ray spectrum is acquired using a logging string employing a neutron source and a natural gamma ray sensor.

Abstract: A method for separating and quantifying gamma ray induced and neutron induced responses in a radiation detector includes detecting radiation in a radiation field comprising neutrons and gamma rays. The detected events are converted into a detector pulse amplitude spectrum. The pulse amplitude spectrum is decomposed into contributions from detected gamma rays and detected neutrons using gamma ray standard spectra and neutron standard spectra and a spectral fitting procedure which results in a best fit between a weighted sum of the contributions and the detector pulse amplitude spectrum. The fitting procedure includes determining fitting parameters for each of the standard spectra wherein at least one of the fitting parameters is different for the gamma ray standard spectra and the neutron standard spectra. In one embodiment, the fitting parameter is spectral gain.

Abstract: A well-logging tool may include a sonde housing, and a radiation generator carried by the sonde housing. The radiation generator may include a generator housing, a target carried by the generator housing, a charged particle source carried by the generator housing to direct charged particles at the target, and at least one voltage source coupled to the charged particle source. The at least one voltage source may include a voltage ladder comprising a plurality of voltage multiplication stages coupled in a bi-polar configuration, and at least one loading coil coupled at at least one intermediate position along the voltage ladder. The well-logging tool may further include at least one radiation detector carried by the sonde housing.

Abstract: A well-logging tool may include a sonde housing and a radiation generator carried by the sonde housing. The radiation generator may include a generator housing, a target carried by the generator housing, a charged particle source carried by the generator housing to direct charged particles at the target, and at least one voltage source coupled to the charged particle source. The at least one voltage source may include a voltage ladder comprising a plurality of voltage multiplication stages coupled in a uni-polar configuration, and at least one loading coil coupled at at least one intermediate position along the voltage ladder. The well-logging tool may further include at least one radiation detector carried by the sonde housing.

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: Methods may include detecting the presence of a component in a wellbore including irradiating an interval of a wellbore containing one or more components of a wellbore tool with a neutron source, wherein the one or more components of the wellbore tool comprise one or more tracer materials; measuring the radiation emitted from the one or more components of a wellbore tool; determining one or more of presence, location, and intensity of the radiation emitted from the one or more components of the wellbore tool. Devices may include a first element comprising one or more tracer materials, wherein the one or more tracer materials emit gamma radiation upon irradiation with a neutron source; wherein the tool is configured to be emplaced in a subterranean formation.

Abstract: A radiation detector package includes a support apparatus at least part of which is constructed from a naturally occurring radioactive material. A scintillator is associated with the support apparatus. The support may include a detector housing carrying a photodetector and the scintillator, and the detector housing may be constructed from the naturally occurring radioactive material.