Understanding Ultracold Neutron Production in Oxygen Solids from Volume   and Temperature Dependent Yields
  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$_2$. 
C.-Y. Liu, C.M. Lavelle, D.J. Salvat, W. Fox, G. Manus, P.M.   McChesney, Y. Shin, A. Couture
nucl-ex cond-mat.mtrl-sci