Scintillators

The TOF and TSC scintillators (BC408, Bicron) were wrapped with one layer of 45 $\mu$m thick polyvinyl film (Tedlar) for light tightness and surface protection. This thin wrapping minimizes the dead space between adjacent TOF counters. Careful measurements of the physical dimensions of all counters were made to ensure the dimensions of each counter consistent with the TOF assembly tolerance.
The attenuation length and light yield of all of the TOF scintillators were measured using a cosmic-ray test stand. A lucite Cerenkov counter was used to suppress low momentum cosmic rays. Fig. (a) shows the result of attenuation length measurements for some of TOF scintillators. The attenuation length was evaluated by using a ratio of signal charges and a time difference between two PMTs of a TOF counter. The measured light propagation velocity was 14.4 cm/ns. The average attenuation length was 3.9 m, which satisfies the specification for the minimum attenuation length of 2.5 m. Fig. (b) shows the result of measurements of light yields seen by each PMT for cosmic rays at the center of a counter.

Figure: (a) Attenuation lengths and (b) light yields of 38 TOF scintillators.