Uniform description of breakup mechanisms in central collision, projectile fragmentation, and proton-induced spallation

Abstract

Background: A diversity of fragmentation modes has been observed in several types of nuclear reactions, which may correspond to different breakup mechanisms.Purpose: The present work is an attempt to compare the mechanisms of the fragment emission in central heavy-ion collision near the Fermi energy, projectile fragmentation, and proton-induced spallation.Method: The collisions until the prefragments with excitation energy less than 2 MeV/nucleon are studied using the isospin-dependent quantum molecular dynamics (IQMD) model, while the evaporations of light particles from the prefragments are described by the statistical code gemini. In the IQMD model, the binary nucleon-nucleon collisions with the Pauli blocking are applied to treat some features of fermionic motion phenomenologically. However, the binary collisions are scarce in the region where the relative momenta between the nucleons are small. Thus, the method of the phase space density constraint (PSDC) are applied in the IQMD model in order to treat phenomenologically the features of fermionic motion.Results: The calculations of various observables are compared to the available data. The comparison not only shows the similar regularities of the calculations to the data, but also emphasizes the role of the PSDC method. The dynamical $E\ensuremath{-}\ensuremath{\rho}$ trajectories show that the compression-expansion phase in the central HIC near the Fermi energy results in the spinodal decomposition. While in the projectile fragmentation and proton-induced spallation, the projectiles are heated without compression and then cool down with slight expansion. However, driven by the dynamical fluctuations, the spinodal instability is possible for a part of the events. The perhaps most important result of this study is the significant role of the fermionic feature in the mechanisms of the fragment emission.Conclusions: The $\mathrm{IQMD}+\mathrm{GEMINI}$ framework provides a uniform description of breakup mechanisms in central collision, projectile fragmentation, and proton-induced spallation.