Neutron fibres: a possible application of neutron optics

Abstract

The authors study confined propagation of slow (thermal) neutrons along (non-hollow) solid fibres made of certain elements (Ti, Mn, ...) such that amplitude for the low-energy nuclear scattering of neutrons on them be negative. Geometrical optics and quasiclassical descriptions, procedures for confining the neutrons, and some applications to radiotherapy are outlined. The confined propagation modes for slow neutrons along infinite homogeneous circular fibres without and with nuclear absorption are analysed. Some estimates of the spectral density in the neutron flux and its attenuation are outlined. In order to assess lattice periodicity effects, the potential seen by a neutron inside an infinite periodic solid fibre and its confined propagation are discussed in detail. Here the authors find wide allowed and small forbidden bands for the neutron energy along the periodic fibre: well inside the allowed bands the neutron propagation modes reduce, as a first approximation, to those for the homogeneous fibre. Lattice vibration effects and the penetration, confinement and eventual scattering of neutrons by a homogeneous fibre are also analysed.