A class of logging-while-drilling (LWD) imaging tools that work from the interaction of gamma rays with a formation. An orientated rotating nuclear source of gamma rays interacts with the borehole wall, and through Compton scattering and photoelectric absorption, measurements are transformed into bulk density and PEF determinations. Such data are placed into equally spaced azimuthal bins leading to oriented measurements, allowing low-resolution borehole images to be produced. These devices will work in both water and oil based environments, and, with examples as yet unknown to the authors, possibly in hole sections with no drilling fluids or water present.
LUTHI, S. M. 2000. Geological Well Logs. Springer, Berlin, p373.