Feasibility study of a new surrogate reaction experimentto constrain neutron capture cross sections on radioactive isotope with Geant4 simulations

Neutron capture (n,γ) cross sections on short-lived isotopes are important for basic and applied nuclear science. (n,γ) cross sections on short-lived isotopes require indirect measurements as direct measurements using a neutron beam are nearly impossible. Thus, indirect techniques such as surrogate methods and Oslo methods using charged-particle reactions or β-decays have been developed in past decades. Despite many theoretical and experimental efforts, accurately constraining the cross sections by those indirect techniques is difficult. The reason is that key ingredients for Hauser-Feshbach calculations such as photon strength function and nuclear level densities are elusive, due in large part to uncertain spin-parity (Jπ) distributions of compound nuclei (CN) populated by the indirect techniques. In this project, we develop a new technique to accurately constrain the Jπ distributions of the CN populated by (d,p) and test its feasibility in an actual surrogate reaction experiment that we plan at GANIL using Geant4 simulations. The planned experiment performs 85Kr(d,p)86Kr measurements as a surrogate for 85Kr(n,γ) using a pure 85Kr radioactive ion beam with state-of-the-art detectors: the VAMOS, a Si detector, and EXOGAM γ-ray detectors. We estimated (d,p) cross sections with FRESCO and the CN γ decay scheme for 86Kr with DICEBOX, and then incorporated them within our simulations. We used the intensities of primary γ-rays from CN as a probe to constrain the J𝝅 distributions and the carefully simulated results proved the feasibility with a limited intensity (105-6 ions/sec) of RI beams. This new technique thus can improve the accuracy to constrain the photon strength functions and structural information, ultimately (n,γ) cross sections, and could be applicable for future experiments, e.g., at FRIB.