Plastic Ball Flies to CERN—And Higher Energies

At the Lawrence Berkeley Lab's Bevalac in February, the Plastic Ball nuclear particle detector was being carefully crated for its jumbo‐jet flight to CERN—and higher heavy‐ion energies. For the past four years, this hollow, faceted ball of $814 plastic/CaF2$ scintillation modules has been monitoring the fragments coming off high‐energy heavy‐ion collisions at the Bevalac, which can accelerate heavy‐ion beams to 2 GeV/nucleon. From the outside, we see mostly the cabled ends of photomultiplier tubes. The Plastic Ball, built at LBL in collaboration with the Gesellschaft fur Schwerionenforschung (GSI) in Darmstadt, was the first nuclear‐physics detector capable of simultaneously identifying and measuring essentially all of the charged particles produced in a high‐energy heavy‐ion collision. Among the Plastic Ball's successes has been the first observation of “collective flow” in compressed nuclear matter.