Isospin effects in heavy ion reactions and the role of neutron detection

Brunilde Gnoffo (Università degli Studi di Catania, Italy)

Heavy-ion collisions at low and intermediate energy provide a unique opportunity to investigate a wide variety of reaction mechanisms, including fusion, fission, multifragmentation, and projectile/target breakup. Besides, at these energies, the isospin degree of freedom plays a crucial role in the competition among these mechanisms, influencing fragment production and reaction dynamics.
These aspects were investigated within the ISODEC experiment through the study of the reactions 86Kr + 48Ca and 78Kr + 40Ca at 10 AMeV, performed with the CHIMERA multidetector. The analysis of velocity and energy spectra, charge and mass distributions, revealed significant differences between the two systems. In central collisions, the neutron-poor system exhibited a higher probability of fission-like processes, while the neutron-rich system showed a slightly enhanced fusion-evaporation cross section. In more peripheral collisions, the breakup of the quasi-projectile displayed a predominantly dynamical character, particularly for the neutron-rich system.
The influence of isospin on the thermodynamic properties of the reaction products was also investigated. Temperatures were extracted using different thermometers based on alpha-particle energy spectra and isotope yield ratios. For fusion-evaporation events, higher temperatures were observed in the neutron-rich system regardless of the method employed. Conversely, the quasi-projectile formed in peripheral collisions exhibited lower temperatures for the neutron-rich system.
The natural extension of these studies is the use of radioactive ion beams, which allow access to nuclei with extreme neutron-to-proton asymmetries and provide valuable constraints on theoretical models describing nuclear dynamics and statistical decay processes.
A key requirement for these investigations is the complete reconstruction of reaction events. In this context, neutron detection plays a fundamental role. The NArCoS detector, currently under development at INFN Sezione di Catania and Laboratori Nazionali del Sud, represents a unique opportunity to improve event characterization and gain crucial information on reaction mechanisms involving neutron emission.