Ga surrogate measurement to inform i-process nucleosynthesis*

A recent study of the metal-poor star HD94028 observed several isotopic abundance ratios (As/Ge, Se/As among others) that were not explained only by summing s- and r-process abundance distributions. A new neutron-capture driven nucleosynthetic process named the i-process has been proposed to explain this observation, taking place at neutron densities intermediate to that observed in the s- and r-processes. A subsequent sensitivity study performed using a one zone simulation to match the observed HD94028 abundances identified the ⁷⁵Ga(n,γ)⁷⁶Ga reaction rate to be the most significant, with variations in this rate showing a strong anti-correlation to the predicted As abundance. Efforts are now underway to use the GODDESS detector system to inform the ⁷⁵Ga(n,γ)⁷⁶Ga reaction rate for the first time at the Facility for Rare Isotope Beams (FRIB) using the ⁷⁵Ga(d,pγ)⁷⁶Ga reaction as a surrogate. A novel surrogate reaction approach that detects protons and heavy charged-particle products in coincidence is proposed to attain improved detection efficiency compared to the traditional approach using only proton-γ coincidences. Simulations, instrumentation, and other developments in preparation of the experiment will be discussed.