Equilibration chronometry and reaction dynamics
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© 2018 Societa Italiana di Fisica. All Rights Reserved. Heavy-ion collisions exhibit a complex and beautiful variety of behavior which arises from the dynamic interplay of competing forces. The nuclear equation of state governs this behavior, and by studying this behavior we have formed an understanding of the equation of state. The low-density neck which is very pronounced in heavy-ion collisions below the balance energy plays many roles. The neck acts as a sink for neutrons, and also acts as a bridge to allow neutron-proton equilibration and mass exchange between the reaction partners. The material in the neck can be released as free nucleons, or can aggregate into clusters. The neck will rupture at least once as the reaction partners re-separate, but can rupture in multiple places with measurable delay between the ruptures. We have recently characterized neutron-proton equilibration in heavy-ion reactions in an unprecedented level of detail. We examine here the measured composition of the remnant of the projectile and the largest remnant of the neck. These compositions show both a clear dependence with rotation angle, and as the heavy fragment becomes more neutron-rich, the light fragment becomes less neutron-rich. The rotation angle is interpreted as a measure of the duration of contact; not only is a timescale extracted for neutron-proton equilibration but it is observed that the composition changes exponentially in time, consistent with a process following first-order kinetics. The results are robust with respect to the impacts of secondary decay, the background of statistical decay, and choice of alignment angle definition. The equilibration is seen for a broad range of final states and for beam and target combinations with varying initial neutron richness.
author list (cited authors)
Rodriguez Manso, A., McIntosh, A. B., Hagel, K., Heilborn, L., Jedele, A., Wakhle, A., Zarrella, A., & Yennello, S. J.