An electron linac as an X-ray source for measuring geological density

Abstract

Radioactive isotopes are generally used as the photon source for measurements in the wellbore of the density of geological formations. The source must be strong for meaningful count rates to be obtained at reasonable logging speeds. Schlumberger-Doll Research has undertaken a research program to replace the radioactive source with an electrically switchable source. In this paper, we report the use of an electron linac to produce a bremsstahlung photon beam to measure geological density. A commercial radiography electron linac was modified to extract the pulsed electron beam from the accelerator. The beam was transported in an evacuated beam line inserted into the borehole of a laboratory formation. The beam was bent by an electromagnet and onto a high- Z target. The resulting bremsstrahlung radiation was thus directed into the geological material to be probed. Beam characteristics, such as amplitude changes, spot size, and energy, that affect the density measurements were investigated. Normalization methods requiring good characterization of these phenomena have been developed.