Raman Spectroscopy as a way to determine Ortho to Para Ratio of Deuterium

A superthermal ultracold ($<$350 neV) neutron source using a solid Deuterium (D$_{2}$) crystal is being developed at the NC State University PULSTAR nuclear reactor. Ultracold neutron production in the solid D$_{2}$ crystal requires that the D$_{2} $ be in the ortho (total nuclear spin of 0) rotational state, as D$_{2}$ in the para (spin 1) rotational state interacts with ultracold neutrons by transferring energy to the neutrons. A novel method to determine the ortho/para-D$_{2}$ ratio is to use Raman spectroscopy to determine the fraction of rotational states in the D$_{2}$. This project focuses on the design, construction, and ultimate use of a double-grating Raman spectrometer to determine the ratio of ortho-D$_{2}$ to para-D$_ {2}$. This system is critical to the optimization of the para-to- ortho-D$_{2}$ converter which produces D$_{2}$ for the ultracold neutron source. I will present details on the Raman spectrometer's construction and performance, as well as Raman spectra obtained for air and regular D$_{2}$ (with 30\% para-D$_ {2}$ content).