Plastic Scintillation Detectors for Time-of-Flight Mass Measurements

Fast timing detectors are an essential element in the experimental setup for time-of-flight (ToF) mass measurements of unstable nuclei. We have upgraded the scintillator detectors used in experiments at the National Superconducting Cyclotron Laboratory (NSCL) by increasing the number of photomultiplier tubes that read out their light signals to four per detector, and characterized them in a test experiment with $^{48}$Ca beam at the NSCL. The new detectors achieved a time resolution ($\sigma$) of 7.5 ps. We systematically investigated different factors that affect their timing performance. In addition, we evaluated the ability of positioning the hitting points on the scintillator using the timing information and obtained a resolution ($\sigma$) below 1 mm for well-defined beam spots.