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The dynamical structure factor of solid $^{15}$N$_{2}$ in the $\alpha$ phase($T<35$K) is measured at the IN4 time-of-flight spectrometer at the InstitutLaue Langevin, and the potential performance of this substance as a UCNconverter is assessed. The cross-section to down-scatter neutrons to ultra-coldneutron energies is determined as a function of incident energy, as well as theup-scattering mean free path. The UCN production cross-section is found to beapproximately 20% of that of deuterium. However, UCN with energy 181 neV havean up-scattering mean free path of 46 cm at $T=5.9$ K, which is $\sim20$ timeslarger than deuterium. Therefore, a large volume $\alpha-^{15}$N$_{2}$ sourcemay produce an improved UCN density if sufficient isotopic purity can beachieved.

Investigating solid $\alpha-^{15}$N$_{2}$ as a new source of ultra-cold neutrons