Abstract: A pressure pulse generator for use in MWD operations in a drilling installation having a drillstring, a drilling bit, means for supply drilling fluid via the interior of the drillstring to the drilling bit, and an annulus between the drillstring and the wall of the bore hole being formed. The pressure generator generates a pressure pulse signal in the drilling fluid which transmits such signal to pressure monitoring equipment at the surface. The pressure pulse generator includes an outer housing which can be mounted in a drillstring component, and in which the operating components of the pulse generator are housed; a main valve having a valve operating chamber which allows drilling fluid to pass from the interior of the drillstring to the exterior when the valve is opened, and thereby to generator a pressure pulse signal that travels to the surface.

Abstract: A gamma ray detector and measurement device having a generally elongate housing (11); a scintillator module (12) movably mounted in the housing (11) and arranged to respond to the presence of gamma rays in the local environment in which the device is located and which rays pass through the wall (13) of the housing and into the scintillator module, the module having an optical output (14) for transmitting an optical signal based on converted incoming gamma rays and an optical transducer module (15) also movably mounted in the housing (11) and having an input (16) arranged to receive the optical output from the scintillator module, the transducer module being able to convert the instantaneous optical output into an electrical output corresponding to the energy and flux of the incoming gamma radiation as detected in the scintillator module; in which the output (14) of the scintillator module (12) and the input of the transducer module (15) are closely spaced to each other, and define a space (17) therebetween to