Mass Resolution of the Scintillating Optical Fiber Isotope Experiment (SOFIE)

In December, 1990, we exposed the Scintillating Optical Fiber Isotope Experiment (SOFIE) to beams of silicon and iron nuclei at the LBL Bevalac accelerator. SOFIE is a Cerenkov-dE/dx-range balloon experiment designed to study the isotopic composition of heavy galactic cosmic rays. Newly developed detectors using scintillating optical fiber technology provide high-resolution trajectory and range measurements in a large-area detector. An Analysis of the Bevalac data is presented, including performance of the trajectory, Cerenkov and range detectors, and mass resolution at silicon and iron. We find the mass resolution to be ~0.26amu at silicon and ~ 0.4amu at iron, consistent with predictions based on the expected sources of error in the Cerenkov and range detectors.