Complete Phenomenological Model for Projectile-Breakup Reactions

One of the important goals of the FENDL-3 development project is the inclusion of deuteron- induced reactions in the data library. This will rely heavily on reaction model calculations, but general reaction model codes typically lack a model for the deuteron-breakup mechanism, which makes important contributions at almost all incident energies. The development of a robust projectile-breakup model is, therefore, an important priority for the FENDL-3 Coordinated Research Project. Projectile breakup is here defined as the emission of a projectile fragment with a fairly narrow energy distribution peaked at an emission energy corresponding to the projectile velocity. These fragments are emitted with an angular distribution that is more sharply peaked toward forward angles than the surrounding and underlying cross section. When the undetected fragment interacts with the target nucleus, it forms a composite system that will then undergo energy equilibration. Particle emission occurring during and after that equilibration will need to be included in reaction model codes. The question of projectile breakup, however, extends beyond deuterons. The breakup mechanism also makes significant contributions for reactions induced by 3He ions and, at sufficiently high incident energies, by α-particles. Until a model for this mechanism is included in pre-equilibrium-model reaction codes, it is impossible to finalize the benchmarking of these codes for complex-particle-induced reactions. In particular, a definitive assignment of the initial particle-hole configuration in the exciton model cannot be made for complex-particle projectiles, because projectile breakup is expected to significantly reduce the amount of the total reaction cross section going into the main exciton-model equilibration calculations. Given the importance of the projectile-breakup mechanism, both from a basic physics perspective and for energy applications, a phenomenological breakup model has been developed. It is designed for inclusion in the next release of the Triangle Universities Nuclear Laboratory pre-equilibrium reaction code PRECO and in larger, more comprehensive Hauser-Feshbach model codes such as GNASH and TALYS