Measurement of the isomer production ratio for the 112Cd(n,γ)113Cd reaction using neutron beams at J-PARC

The astrophysical origin of a rare isotope Sn-115 remains an open question. An isomer (T-1/2 = 14.1 y) in Cd-113 is an s-process branching point from which a nucleosynthesis flow reaches 115Sn. The s-process abundance of Sn-115 depends on the isomer production ratio in the Cd-112(n,gamma)Cd-113 reaction. However, the ratio has not been measured in an energy region higher than the thermal energy. We have measured gamma rays following neutron capture reactions on Cd-112 using two cluster high-purity germanium (HPGe) detectors in conjunction with a time-of-flight method at J-PARC. We have obtained the result that the relative gamma-ray intensity ratio of the isomer is almost constant in an energy region of up to 5 keV. This result suggests that the s-process contribution to the solar abundance of Sn-115 is minor. We have found that the ratio of a resonance at 737 eV is about 1.5 times higher than other ratios. This enhancement can be explained by a p-wave neutron capture. This result suggests measurements of decay gamma rays to isomers are effective to assign the spin and parity for neutron capture resonances.