A new experimental apparatus called the accurate neutron nucleus reaction mea­surement instrument (ANNRI) has been constructed on the beam line no. 4 (BL04) of the MLF in the J-PARC. The ANNRI has two detector systems. One of them is a large Ge detector array, which consists of two cluster-Ge detectors, eight coaxial­shaped Ge detectors, and BGO Compton suppression detectors; the other is a large NaI(Tl) spectrometer (Fig. 5.3). The ANNRI has an advantage for neutron cross­section measurements because the MLF facility can provide the strongest neutron intensity in the world.

The neutron capture cross sections of 237Np [32, 33], 241Am [34], 244Cm [35], 93Zr [36], 99Tc [37], and 107Pd [38] have been measured relative to the 10B(n, ay) standard cross section by the TOF method. Some highlights of results obtained in our research activities are shown in Fig. 5.4 for 237Np and in Fig. 5.5 for 93Zr.

This work

О Weston(1981) □ Esch(2008)

Neutron energy (ev)

Fig. 5.4 241Am cross section in neutron energy from 0.01 to 10 eV

The results obtained at the ANNRI are good agreement with the data reported by Weston (Fig. 5.4). The 93Zr cross sections in Fig. 5.5 present results greatly different from the evaluated data in the thermal neutron energy region. One finds that the present results support the value of the thermal cross section reported in 2007 [39].

5.2 Summary

This chapter described the JAEA research activities for the measurement of neutron capture cross sections for LLFPs and MAs by activation and neutron time-of-flight (TOF) methods. We summarized our results of the thermal neutron capture cross

Neutron energy (eV)

93Zr cross section (tentative data) together with the evaluated data

section and the resonance integral for some of the important LLFPs and MAs by the activation method.

Operation of a new experimental apparatus called the accurate neutron nucleus reaction measurement instrument (ANNRI) in the MLF at J-PARC has been started for neutron capture cross-section measurements of MAs and LLFPs. Some of the highlights of our results have been shown here.

Acknowledgments The authors thank the staff at Kyoto University Reactor Institute, Rikkyo University Reactor and JRR-3M. A part of this work has been carried out under the Visiting Researcher’s Program of the Research Reactor Institute, Kyoto University. Moreover, the authors appreciate the accelerator staff of J-PARC for their operation of the accelerator.

This work is supported by JSPS KAKENHI (22226016).

Open Access This chapter is distributed under the terms of the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.