Measurements of Capture Gamma Rays from the Neutron Resonances of 74Se and 77Se at the J-PARC/MLF/ANNRI

Neutron resonance capture γ-ray measurements on 74Se and 77Se were performed with a 4π Ge spectrometer in the Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex (J-PARC). The relative intensities of primary transitions were derived for the 27-eV resonance of 74Se and the 113-, 212-, 291-, 342-, 690- and 864-eV resonances of 77Se, respectively. For the 27-eV resonance of 74Se, a strong transition to the 293-keV state was observed. Moreover, new resonances of 74Se were found at 6, 123, 436 and 640 eV. It was confirmed that those resonances had originated in the neutron capture reaction of 74Se by obtaining the TOF spectrum corresponding to the strong 287-keV ground-state transition γ ray. As for 77Se, differences of the decay pattern were found between the resonances.