In-core detectors should have wide application in the reactor safety program. A detector development program has been underway at Argonne National Laboratory to provide in-core detectors which are either neutron or gamma sensitive. The present paper describes one of the detectors under consideration for in-core fuel motion monitoring. It is gamma sensitive and has been tested in the core region of the Argonne Research Reactor (CP-5). The detector performed well over a 5-week period and yielded a directional discrimination factor, front to back, of 10 to 1, in good agreement with earlier tests conducted using a low power reactor and a radium source.