A component of a production-logging tool that carries a radioactive solution (often carnotite) that can be selectively released into a flow stream. When the radioactive solution is released into an injected fluid, the movement of the mixture can be traced by gamma ray detectors located in the tool.Radioactive tracers are generally used in injection wells rather than in production wells to avoid radioactive contamination at the surface. The main applications of radioactive tracers include establishing flow profiles in injection wells, detecting fluid movements behind the pipe, and locating leaking packers and fluid movement between wells.