Deterioration of pulse-shape discrimination in liquid organic scintillator at high energies

The pulse shape discrimination (PSD) is often made for liquid organic scintillators for the purpose of separating neutrons from gamma-rays. Particles emitted from spallation reactions induced by protons of GeV range were measured with an NE213 liquid scintillator, 12.7 cm in diameter and 12.7 cm thick. The pulse shape characteristics were studied by the use of charged-particles incident on the detector. A two-gate integration method. The charged particles (protons and pions) having velocities below β=0.133 were identified into the conventional recoil-proton like events. On the contrary, the charged particles aboveβ=0.133 were classified as the electron-like events in the PSD. The PSD was useful only for neutrons which produce recoil protons stopping within the scintillator. The experimental results suggest that a great care should be taken in the PSD for separation of intermediate-energy neutrons from gamma-rays.