A "4 Ge spectrometer" for measurements of neutron capture cross sections by the time-of-flight method at the J-PARC/MLF/ANNRI

Kin, Tadahiro; Furutaka, Kazuyoshi  ; Goko, Shinji*; Harada, Hideo   ; Kimura, Atsushi   ; Kitatani, Fumito  ; Nakamura, Shoji  ; Ota, Masayuki*; Oshima, Masumi; Toh, Yosuke   ; Hori, Junichi*; Igashira, Masayuki*; Katabuchi, Tatsuya*; Koizumi, Mitsuo ; Mizumoto, Motoharu*; Kamiyama, Takashi*; Kino, Koichi*; Kiyanagi, Yoshiaki*

For the developments of advanced reactors such as fast breeder reactors or accelerator driven systems, nuclear data of minor actinides (MAs) and long-lived fission products (LLFPs) are important. However, these data are insufficient at present in quantity and quality. To overcome/improve such a situation, we have developed a 4 germanium spectrometer to measure neutron capture cross sections of MAs and LLFPs by the time-of-flight (TOF) method. The spectrometer was installed in the MLF in the J-PARC. At the conference, we will report a result of a measurement of the neutron capture cross section for gold by the TOF method to develop an analysis method. The analysis methods will be used for MAs and LLFPs. During the experiment for gold, the accelerator of J-PARC was operated in so called "double-bunch mode". In the mode, protons injected to the Japan Spallation Neutron Source (JSNS) have a time structure. The time structure affects TOF measurements. Mainly the accelerator is operated in the mode, it is important to know the effect. We found dead-time effect can be corrected by using a random-pulse generator. Background components can be removed with results of measurements of a blank sample. The cross section measured was normalized by the value in ENDF B/VII at the thermal energy. Finally, the cross section of gold in the incident neutron energy range from the thermal to 10 keV was obtained. Because the result is in good agreement with ENDF B/VII, we found the analysis method can be applied for experimental data obtained with the spectrometer.