Directly Measured Neutron-Induced Reactions on Radioactive Nuclides for Nuclear Astrophysics*

In nucleosynthesis network calculations, available nuclear physics inputs are limited to the measurements on stable or accessible radioactive nuclei, remaining thousands of reactions, crucial for astrophysical implications, to rely on the theoretically predicted reaction rates. Hauser-Feshbach (HF) formalism is widely used to predict these reaction cross sections, however difficulties like renormalizations of calculated neutron-induced reaction cross sections to experimental observables, or energy-dependent shape discrepancies among different HF calculations have been addressed. Direct, high-precision measurements provide not only cross sections, also validate HF parameters for enhancing the fidelity of theoretical predictions.

 

At Los Alamos Neutron Science Center (LANSCE), neutrons are produced in the energy range of thermal to several-hundred MeV, to measure cross sections. Instruments used for nuclear astrophysics interest are DANCE (Detector for Advanced Neutron Capture Experiments) for neutron captures, DICER (Device for Indirect Capture Experiments on Radionuclides) for total cross sections, and LENZ (Low Energy NZ) for neutron-induced charged particle emitting reactions. At the Isotope Production Facility in LANL, the radioactive target fabrication techniques were developed. I will present the on-going, exploratory effort of reaction studies on radionuclides and report the first, direct measurement of the ⁵⁶Ni(n,p) reaction, to confirm the importance of νp process during neutrino-wind driven environments. For expanding the current capability, I will conclude with the outlook on the neutron target facility development at LANSCE.