  We investigate the propagation of ultra-high energy cosmic ray nuclei (A =
1-56) from cosmologically distant sources through the cosmic radiation
backgrounds. Various models for the injected composition and spectrum and of
the cosmic infra-red background are studied using updated photo-disintegration
cross-sections. The observational data on the spectrum and the composition of
ultra-high energy cosmic rays are jointly consistent with a model where all of
the injected primary cosmic rays are iron nuclei (or a mixture of heavy and
light nuclei).
