A High Fidelity Scintillating Fiber Tracker for SONTRAC

We report progress in the development of precision scintillating plastic fiber bundles for 3-d tracking experiments. Specifically, we present an approach for the design and fabrication of the tracking detector for the SOlar Neutron TRACking experiment (SONTRAC), an imaging spectrometer for measurement of 20-200 MeV neutrons in a space environment. SONTRAC operates by measuring the tracks of the recoil protons from n-p scatters in a closely packed bundle of scintillating plastic fibers. The energy and angular resolution of the instrument depends on the accuracy and precision with which the length and orientation of each track can be measured. Early prototype fiber bundles yielded distorted track images due to irregular orientation and registration of the fibers. These fiber detector bundles, composed of 250 mum square scintillating plastic fibers on a nominal 300 mum pitch, contain fibers with registration errors as large as 1 mm. The next fiber bundles will use 290 mum round fibers on 300 mum pitch. The goal is for every fiber in the array to be registered within 300 mum of a rectilinear 3-d grid. We present the requirements, materials, assembly fixtures and procedures for the fabrication of these higher fidelity SONTRAC fiber bundle detectors. We present photographs and measurements of a small prototype fiber bundle constructed using these new techniques.