Nuclear data for multiple prompt gamma-ray analysis

Most of nuclei emit two or more prompt gamma rays in the neutron capture reaction. In multiple prompt gamma-ray analysis (MPGA), the gamma rays are simultaneously measured by two or more sets of gamma-ray detectors; these gamma rays are reduced to a pair of two prompt gamma rays, and it is added to the two-dimensional spectrum, which sets two energy axes. A gamma-ray peak corresponding to the pair of gamma rays that are emitted simultaneously will appear on the two-dimensional spectrum. By analyzing this two-dimensional peak, resolution can be raised by leaps and bounds. MPGA needs not only the knowledge of energies of capture gamma rays, but also nuclear level structure data. While the energies are usually accurate, many of the excited level structures are poorly known. Complete sets of these nuclear data are of great importance. A new MPGA system will be constructed at the guide-hall of JRR-3M in Japan Atomic Energy Research Institute. This system consists of three clover Ge detectors with anti-Compton suppressors. The absolute efficiency of the system is about 10% for a 1.3-MeV gamma ray. It will be widely used in the fields of agriculture, engineering, geosciences, environmental science, and measurement of neutron capture cross sections of minor actinides.