Fluence standard of 14 MeV neutrons by associated particle method and its application for 56Fe(n, p)56Mn cross section measurement

A new system for measuring associated α particles produced by T(d, n)α reactions has been made to evaluate the mean energy of neutrons and also to determine the rate of the neutron emission from the target simultaneously. The fluences at 890 and 1310 to the incident deuteron beam are measured with the Si surface barrier detectors positioned (999.3+-0.005) mm apart from the target. The total counts of α spectra are obtained by adjusting the lower discrimination level of the single channel analyzer at the midpoint of the tail part following to the main peak. The solid angle conversion factor (SACF) from the Center of Mass system to the Laboratory system is determined corresponding to the measured mean energy of neutrons. The neutron energy produced by the T(d, n) α reaction is determined by the ratio of the fluences at 890 and 1310, taking the theoretical angular distribution of particles into account. The neutron attenuations and the secondary neutron products in the target holder, air and the room are estimated by PALLAS code. The neutron (n,p) cross section of 56Fe has been measured using the neutron standard field described above. The value has been measured to be 110.9+-1.4 mb at 14.58+-0.03 MeV. (author)