An example apparatus includes an outer housing and a drive shaft at least partially within and rotationally independent from the outer housing. A drill bit may be coupled to the drive shaft. At least one gamma ray sensor may be rotationally coupled to the drive shaft within the outer housing. In certain embodiments, the apparatus further includes a housing rotationally coupled to the drive shaft, wherein the housing comprises at least one pressurized cavity; and the at least one gamma ray sensor is located within the at least one pressurized cavity.