 The gadolinium quickly captured the neutrons produced in the inverse beta decay.The second region (region II) contained 17 tons of undoped scintillator to capture the electromagnetic energy from the inverse beta decay (≈99%) and the photons from the neutron capture in the Gd (>95%).The outer surface of region II contained 192 inward facing photomultiplier tubes (PMT) held in an opaque plastic structure.