A liquid scintillator cosmic ray active shield

We describe the prototype for an active cosmic ray shield for a neutrino oscillation experiment to be performed at LAMPF. This shield is a large liquid scintillator-filled steel tank viewed by an array of large hemispherical photomultiplier tubes. We discuss the motivation for choosing a liquid scintillation counter and details of its implementation. Results of prototype tests, and tests on liquid scintillator properties, are presented.