Extension of the particle x-ray coincidence technique: The lifetimes and branching ratios apparatus

The particle x-ray coincidence technique (PXCT) was originally developed to measure average lifetimes in the 10-17-10-15s range for proton-unbound states populated by electron capture (EC). We have designed and built the Lifetimes and Branching Ratios Apparatus (LIBRA) to be used in the stopped-beam area at the Facility for Rare Isotope Beams that extends PXCT to measure lifetimes and decay branching ratios of resonances populated by EC/β+ decay. The first application of LIBRA aims to obtain essential nuclear data from Ga60EC/β+ decay to constrain the thermonuclear rates of the Cu59(p,γ)Zn60 and Cu59(p,α)Ni56 reactions, and in turn, the strength of the NiCu nucleosynthesis cycle, which is predicted to significantly impact the modeling of type I x-ray burst light curves and the composition of the burst ashes. Detailed theoretical calculations, Monte Carlo simulations, and performance tests with radioactive sources have been conducted to validate the feasibility of employing LIBRA for the Ga60 experiment. LIBRA can be utilized to measure most essential ingredients needed for charged-particle reaction rate calculations in a single experiment, in the absence of direct measurements, which are often impractical for radioactive reactants.