Direct Neutron Measurement (n, 2n) Reaction Cross Sections Experimental Study

(n, 2n) reaction cross section from ¹⁶⁹Tm at 14.3MeV was measured with the direct emitted-neutron coincidence detecting method. The experiment was carried out using abnormal fast neutron TOF spectrometer on the HI-13 Tandem Accelerator at CIAE. After comparing the experimental results with evaluated data, main causes of certain differences between them were analyzed and discussed.As one of important nuclear reactions, (n, 2n) reactions are often used as an indicator of neutron flux in D-T fusion because of rather high reaction threshold energy; (n, 2n) reactions are also necessary in the nuclear engineering because they are one of neutron multiplication reactions.Cross sections for (n, 2n) reactions have usually been measured by the foil activation method which is a precise , economic and convenient method. By using this method, however, appropriate radioisotopes need be produced by the reaction. To compensate the deficiency of the activation method and to complement the experimental methods and technology, in the experiment several detectors were arranged at different positions to measure simultaneously emitted two neutrons. By measuring the energy and angular distribution of the two neutrons with the coincidence detection technique, (n, 2n) reaction cross section was acquired through integral calculation. The elastic cross section and the n-p scattering cross section were taken as the reference in the measurements.In the data processing, Monte-Carlo method was used to simulate the TOF spectrum of elastic-scattering neutron. The ratio of the simulated result to the measured spectrum was used to correct the count of elastic-scattering peak. To analyze (n, 2n) reaction energy spectra, theoretical calculation (SUNF program and EMPIRE-II program) and evaluated data were utilized. Finally, the data measured in CIAE were compared with the evaluated data from CENDL-3.0 and main causes of differences between them were analyzed.