A sliding sleeve casing tool apparatus (10) for use in a casing string in a wellbore comprises a housing (58), a communication port (64) and a sliding sleeve (70) to open and close port (64). A radioactive source (146) is attached to the housing (58), and the orientation of the source may be determined by use of a detector apparatus, such as a rotational gamma ray detector. The casing valve thus may be aligned with the fracture of a zone of interest in the well. A plurality of casing valves may be used, with at least one having a radioactive source.
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