A method for making natural gamma ray measurements includes deploying a logging while drilling tool including an electrical neutron output of the electrical neutron source is modulated and the natural gamma ray sensor is used to make a corresponding gamma ray measurement during at least a portion of the modulation. The gamma ray measurement is processed to obtain a corrected total natural gamma ray measurement of the subterranean formation.

An integrated nuclear sensor includes a scintillator connected directly to the photocathode of a photomultiplier tube. The scintillator may be thermally fused to the photocathode. The scintillator can be supported within a scintillator housing by a potting layer that is formed from an elastomer. The scintillator can include a reflector or a reflective coating applied to the outside surface of the scintillator. The reflective coating can be a vapor deposition coating applied to the scintillator.

An integrated nuclear sensor includes a scintillator connected directly to the photocathode of a photomultiplier tube. The scintillator may be thermally fused to the photocathode. The scintillator can be supported within a scintillator housing by a potting layer that is formed from an elastomer. The scintillator can include a reflector or a reflective coating applied to the outside surface of the scintillator. The reflective coating can be a vapor deposition coating applied to the scintillator.

A system including a logging tool that can detect gamma rays in a wellbore, where the logging tool can have a window formed in an outer surface of a drill collar that allows increased sensitivity of a gamma ray detector assembly housed within the drill collar, with a body of the drill collar radially surrounding the gamma ray detector assembly, where the window can be filled with a material, and where the windows provide increased sensitivity to gamma rays in a wellbore in an azimuthal direction allowing azimuthal mapping of the gamma rays in formation surrounding the wellbore.

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive gamma ray measurements from a gamma ray detector; to generate a spectrum based on the gamma ray measurements, the spectrum including a plurality of channels and count rates for the plurality of channels, wherein a channel number of a channel corresponds to energy values of the received gamma rays; to fit a curve to a portion of the spectrum; to determine a location of the maximum of the first derivative of the curve; and to adjust a gain of the gamma ray detector based on the location of the maximum of the first derivative of the curve. Additional apparatus, systems, and methods are disclosed.

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive gamma ray measurements from a gamma ray detector; to generate a spectrum based on the gamma ray measurements, the spectrum including a plurality of channels and count rates for the plurality of channels, wherein a channel number of a channel corresponds to energy values of the received gamma rays; to fit a curve to a portion of the spectrum; to determine a location of the maximum of the first derivative of the curve; and to adjust a gain of the gamma ray detector based on the location of the maximum of the first derivative of the curve. Additional apparatus, systems, and methods are disclosed.

A scintillator can include an elpasolite scintillator compound. The scintillator can be doped with a Group 2 element, and may also include an activator. The scintillator has an improved core valence luminescence at room temperature as compared to a corresponding elpasolite scintillator compound without the Group 2 dopant. The elpasolite scintillator compound can have significant core valance luminescence at a temperature higher than 125° C. In a particular embodiment, the elpasolite scintillator compound can include Cl and may or may not also include another halide, such as Br or I. The scintillator can be part of an apparatus that detects gamma radiation and neutrons and may allow a relatively simpler pulse discrimination technique to be used to a higher temperature, such as 125° C. to 150° C. before a relatively more complex pulse discrimination technique would be used.

A scintillator can include an elpasolite scintillator compound. The scintillator can be doped with a Group 2 element, and may also include an activator. The scintillator has an improved core valence luminescence at room temperature as compared to a corresponding elpasolite scintillator compound without the Group 2 dopant. The elpasolite scintillator compound can have significant core valance luminescence at a temperature higher than 125° C. In a particular embodiment, the elpasolite scintillator compound can include Cl and may or may not also include another halide, such as Br or I. The scintillator can be part of an apparatus that detects gamma radiation and neutrons and may allow a relatively simpler pulse discrimination technique to be used to a higher temperature, such as 125° C. to 150° C. before a relatively more complex pulse discrimination technique would be used.

Systems and methods for determining the thermal maturity of a rock formation from isotopic values in gases are provided. Isotope values may be obtained from mud gas isotope logging, vitrinite reflectance equivalence values may be determined from core samples using known techniques. A relationship between vitrinite reflectance equivalence and isotopic values, such as carbon-13 methane values, may be determined. The vitrinite reflectance equivalence may then be determined from isotopic values to determine the thermal maturity of rock formations accessed by drilling additional exploration wells.

An example apparatus includes a drill bit body and a leg extending from the drill bit body. A journal may extend from the leg, with a gamma ray detector at least partially within the journal. In certain embodiments, the gamma ray detector may be confined within a pressure protective cavity at least partially within the arm of the journal. In certain embodiments, the gamma ray detector may be a scintillator aligned with at least one of a photomultiplier, photodiodes, or phototransistors.