Patent ID: 8742329

Claim:
A casing string well inspection system comprising: a radioactive source that emits gamma rays having an energy range of 200 to 400 keV and comprising a mixture of gamma active long-lived isotopes; at least two detectors installed coaxially with the radioactive source, at least one of the detectors having an ionization mode and comprising an ionization chamber having a cathode made from a light metal or a combination of light metal and a nonconductive material having a low attenuation coefficient, the ionization chamber comprising at least two collimators made from a high absorption coefficient material and wire anodes, the at least two collimators, cathode, and wire anode surrounding a cylinder shaped core electrode made from a high absorption coefficient material; a first collimator positioned between the radioactive source and a wall of the casing string, the casing string bonded to the well with a cement layer; and a second collimator installed axially between the detectors and the radioactive source, wherein the detectors are gas filled gamma detectors.