We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (${\mathrm{S}\mathrm{D}}_2$). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a ${\mathrm{S}\mathrm{D}}_2$ source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.

• Received 26 September 2001

DOI:https://doi.org/10.1103/PhysRevLett.89.272501