VIRTUAL STATE

Abstract

This review article explains the properties of virtual states and discusses their impact on realistic nuclear
structure and nuclear reaction problems. The first half of the paper defines virtual states as poles of the scattering matrix,
i.e., zeros of the Jost function, and discusses their similarities and differences with bound and (zero energy) resonant states. The second half of the paper provides concrete examples of the effects of virtual states in real nuclear systems. Regarding nuclear structure problems, we demonstrate the valence neutron occupying virtual state plays important roles in the formation of the anomalous  structures in the binary and three-body systems: 9Li + neutron and α + α + neutron. On the other hand, in reaction problems, we address thermal neutron scattering by various targets and discuss the close relationship between the peak structure in the so-called S-wave strength function and the virtual states. By synthesizing the calculation about the neutron scattering, we propose a new reaction picture for thermal neutron absorption reactions.

Keywords: Virtual states, nuclear structure, neutron scattering, neutron capture, nuclear reactions.