FIGURE 3. Neutron spectroscopy for the single run.

The energy scale, given in electron equivalent (e.e.) energy, was calibrated against Compton edges of a series of -ray sources and is proportional to anode charge. a, Pulse shape discrimination (PSD) spectrum. Our PSD variable 'slow light/fast light' is the ratio of integrated light in the tail of the PMT signal generated by an event in the liquid scintillator, to the integrated light around the signal's peak. Electron recoils are in the lower branch, and proton recoils, having longer scintillation decay, are in the upper branch. The events enclosed within the upper region are compared against tabulated pulse shapes, rejecting unusual events such as PMT double pulsing. There were a total of 15,300 valid neutrons over the course of the 400-s run. From the distribution of events, we estimate that the number of electron events leaking into the proton branch is negligible compared to the 1% cosmic background. b, Proton recoil spectrum. Valid neutron events are shown in histogram format. For comparison, we also show our detector's simulated^20,21 responses to 1.45 MeV, 2.45 MeV and 3.45 MeV centre-of-mass boosted neutrons.