Can Coulomb breakup of $N=Z$ clustered nuclei constrain capture cross sections? Analyzing the $α(d,γ){}^{6}\mathrm{Li}$ case

Abstract

In nuclear astrophysics, it is fundamental to measure the cross section of radiative-capture reactions involving charged particles at low energy. However, this endeavor is difficult. Coulomb breakup of nuclei on heavy targets has been proposed as an indirect method to infer the low-energy cross sections, because this reaction corresponds to the time reversed process of radiative capture. Two Coulomb breakup experiments aiming to infer the $α(d,γ){}^{6}\mathrm{Li}$ radiative-capture cross section have been performed at 26 MeV/nucleon and 150 MeV/nucleon. Within a fully dynamical reaction model, we report here on a new theoretical analysis of these reactions. Our analysis indicates that the breakup of ${}^6\mathrm{Li}$ onto ${}^{208}\mathrm{Pb}$ is nuclear dominated at forward angles because Coulomb breakup is suppressed due to the $N=Z$ cluster structure of ${}^6\mathrm{Li}$. Our analysis also suggests that the reaction is characterized by marked Coulomb-nuclear interferences. Moreover, we find that higher-order effects considerably increase the breakup cross section at low energies. Consequently, extracting radiative capture cross sections from the breakup reaction data in this case is extremely challenging. We suggest that the forward Coulomb breakup suppression is a general feature of collision processes involving $N=Z$ clustered nuclei. Our findings underscore the importance of advancing alternative indirect methods for nuclear reactions in astrophysics such as electron-induced dissociation.