Figure 2: Energy calibration curve. The total charge in the signal region is proportional to the energy of the α particle below 4 MeV. is confirmed below 4 MeV. α particles of energy more than 4 MeV are so energetic that they can penetrate a CCD detection volume thickness of 20 µ m. When the neutron rate is 100 events/frame, more than one event is ob- served inside one signal region. The performance of neutron detectors with a $^{10}$B converter and a $^{6}$Li converter are tested with neutrons from reactors. The neutron detection efficiency is measured using UCNs supplied at the PF2 beam line of Institut Laue–Langevin in France. Fig. 3 shows the energy 4.1. Neutron detection efficiency 7 4. Neutron beam test