  We present experimental data on ultracold neutron (UCN) production in solid
oxygen from 5 K to 50 K. The experiment used 3 cells of different dimensions in
order to study the excess UCN elastic scattering in s-O$_2$ due to source
density non-uniformities. We present a combined $\chi^2$ analysis with the aid
of Monte-Carlo simulations which contain the detailed physics of UCN transport
as well as cold neutron attenuation. The results validate the UCN production
and upscattering cross-sections extracted from the dynamic structure function
derived from inelastic neutron scattering, and illustrate the role of magnetic
scattering in enhancing UCN production in s-O$_2$.
