Comprehensive analysis of precompound emission: Role of shell closure and target deformation

The present work on low-energy reaction dynamics recognizes the importance of precompound emission as a paramount deexcitation process for emitting energetic particles, even at energies as low as $\ensuremath{\approx}4--5$ MeV/nucleon, where the compound nucleus process has been identified as the sole contributor. This recognition is achieved by performing a comprehensive analysis of cross-section data for a large number of ($\ensuremath{\alpha},n$) reactions within the framework of the theoretical model-based codes cascade, pace4, and talys at varying energies above the Coulomb barrier. The analysis of the data provides a precise estimation of the precompound contribution with respect to its compound nucleus counterpart. Consistency in the rising trends of the precompound curves with the excitation energy and the atomic mass number of target nuclei indicates their origins from a common density domain within the excited nuclei. This commonality establishes a significant interconnection between nuclear structure and reaction dynamics for the participating surface nucleons in precompound process, except those that are emitted from the closed-shell nucleus in the $\ensuremath{\alpha}+_{37}^{85}\mathrm{Rb}\phantom{\rule{4pt}{0ex}}\ensuremath{\Rightarrow}\phantom{\rule{4pt}{0ex}}_{39}^{89}\mathrm{Y}\phantom{\rule{4pt}{0ex}}(N=50)$ reaction. The present investigation explores additional understanding of the target deformation in determining the total precompound contribution.