From the above findings it seems that, although a shaping time constant of 2 ms would be more appropriate for neutron–gamma discrimination, larger values are needed in order to avoid deterioration in resolution and departure from linearity, when neutron energies up to several MeV are being measured. Thus, for both counters the shaping time constant of 6 ms was selected as a compromise between the resolution loss and dead time increment (Fig. 5).
The energy resolution of the two counters as a function of neutron energy is presented in Fig. 8. As expected, the resolution of 3 He counter clearly decreases with neutron energy. Although the resolution of 4He counter seems to follow a similar trend, significant conclusion cannot be drawn because of the relatively high statistical uncertainty.
The energy calibration of the detectors was performed with the neutron beam parallel to the anode wire. For all peaks (i.e. 3He and 4He recoils and 3He(n,p)3H) a linear response with the neutron energy was observed (Fig. 9).