Pulse shape discrimination between gamma rays and neutrons employed in the ARCTERIX prototype. The plot shows the distribution of tail integrals (taken over the last 73% of the signals) divided by the total pulse integrals (“PSD” parameter) vs the pulse height of the PMT signals. The vertical colour scale is indicated on the right. Neutrons and gamma rays were selected by choosing events within the regions indicated by the black and red lines, respectively. The signals saturate at around 6.5 MeV_ee.