Measurement of characteristics of intermediate neutron column

The reactor Yayoi of the University of Tokyo can be used as a lead modulation type spectrometer. An electron linear accelerator is used for the neutron source. The characteristics of the system was measured. The lead assembly is a 2.5 m wide and 2.5 m height octagonal column. The detectors were a micro BF3 counter and a micro fission chamber. The time distribution of neutrons at three experimental points was obtained. A time-energy relation was measured by using various filters. The resolving power determined from the 5.19 eV resonance of Ag was 55.9 percent. The effect of neutron leakage and the absorption by iron are important. The amount of leakage was measured and compared with an estimated value from the Fermi's age theory. The agreement between both values was good. The neutron energy spectrum was obtained. The fission cross sections were evaluated by a fission chamber, and comparison with the group constants was carried out. It was found that the Yayoi intermediate neutron column could be used as a lead moduration spectrometer. (Kato, T.)