Development of a dual counter type neutron spectrometer for the direct measurement of neutron energy spectra

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A full-energy-absorption neutron spectrometer using dual concentric proportional counters has been devised to obtain neutron energy spectra directly from pulse height spectra without unfolding fot neutron energy range from 10 keV to 1 MeV.1. A hollow cylindrical multi-anode proton-recoil counter with a large volume (-5 lit.) filled with propane at 3 atm was designed and constructed to obrain a high proton recoil probabitity, and a commercial _3He counter was installed in the hollow counter coaxially.2. An energy resolution of 23% was obtained with the proton recoil counter for 764 keV equivalent proton energy, and a gamma-ray rejection rate of 95% was attained for gamma-ray energies of the order of 1 MeV using pulse shape discrimination.3. A pulse procession circuit was constructed to obtain delayd coincidence between proton-recoil and neutron-capture signals and to generate gate signals for a multichannel analyzer. Total electronics including the circuit was constructed to analyze the height of full-energy-absorption proton-recoil pulses alone.4. Irradiation of monoenergetic neutrons with an energy berween 80 and 600 keV on the spectrometer evidenced the appearance of a single peak on a pulse height spectrum corresponding to the full-energy-absorption as abserved in the energy response functions calculated by Monte Carlo computer simulation. An energy calibration curve was obtained by using the pulse height spectra. Observed neutron detection efficiencies of the same order as those of calculated assured the reliability of the Monte Carlo calculation.