Excitation of unnatural parity states and proximity of atomic nuclei to the point of the π-condensate instability

It is indicated that inelastic nucleon-nucleus scattering leading to the excitation of unnatural parity states may be a sensitive test of the proximity of nuclei to the point of π-condensate instability. Transition densities for low-lying unnatural parity states in 208Pb are calculated using the theory of finite Fermi systems, explicitly taking into account the one-pion exchange amplitude in the annihilation channel. In the Born approximation, these transition densities yield the differential cross sections with resonance-like enhancement at momentum transfers in the region of the Fermi momentum. This enhacement becomes the more prominent the closer the situation approaches the critical one. The calculated transition densities are tabulated so they may be used for obtaining the differential cross sections in the framework of DWBA and other methods. (Auth.)