Fast neutron measurements using a three-dimensional tracking detector consisting of scintillating fibers have been performed. The detector is composed of 100 layers of 100 0.5mm square fibers each bundled together by 0.5mm thick flat belts. The fibers in consecutive layers are arranged perpendicular to each other. The part where the fibers cross is the detection volume of 5×5×5 cm3. The stack of 100×100 fibers is coupled to an image intensifier. In this study, the detector has been tested with a 650MeV/n 40Ar beam. Although energetic ions and fast neutrons enter the detector simultaneously, the particles can be identified by observing the intensity per unit length of the track. The detector is expected to be used as a space dosimeter for fast neutrons.
