Abstract: A lock structure is disposed in entry and exit passages of sensitive installations, especially nuclear installations, wherein a housing with a revolving gate is arranged in a wall through which said passages extend. Radiation and metal detectors are associated with the lock structure so as to detect radioactive material or weapons being carried through the lock structure. The revolving gate is lockable by latches activated by the detectors so as to lock the revolving gate and prevent passage upon detection of gamma radiation or metal objects.