Estimation of response functions of moderating type neutron detectors by the time-of-flight method combined with a large lead pile

The energy dependent response functions of moderating type neutron detectors having cylindrical polyethylene moderators of 1, 3, 6 and 10 cm thicknesses were determined using the time-of-flight (TOF) technique. By combining the 35 MeV electron linear accelerator with a large lead pile of about 150 t, a pulsed neutron field which is rich in intermediate neutrons was formed and its spectrum at the standard measuring point for the TOF experiment was measured by a Li glass scintillator. In this kind of TOF, the neutron time delay in the polyethylene moderator due to multiple collisions with hydrogen was evaluated by the time dependent neutron transport Monte Carlo code, and compiled to the time response matrix. By using the neutron spectrum at the standard measuring point and the time response matrix, the energy dependent response functions of the moderating type neutron detectors were determined from the measured time spectra for the first time in a considerably wide energy range from a few eV to about 50 keV. The experimental response functions showed good agreement with the calculated results.