Parity non-conserving effects in neutron-nucleus scattering at thermal energies

Abstract

The contribution of the neutron-nucleus component to parity non-conserving effects in neutron-nucleus scattering at thermal energies is considered for several nuclei. The wave function relative to the neutron-nucleus component incorporates for the first time physics which is usually accounted for by optical potential models (strength function and existence of a finite potential scattering length). Different models aiming to reproduce these quantities are developed. Some way to use directly information available from optical model wave functions is also proposed. The various results so obtained show that it is impossible to account for several parity non-conserving effects observed in 81Br, 111Cd, 117Sn and 139La with a single weak neutron-nucleus force, as it should be if the dominant parity admixture was taking place at the level of the neutron-nucleus component. Furthermore, its strength is too large compared to usual expectations. The only explanation left to account for these effects assumes that the dominant parity admixture takes place at the level of the compound nucleus.