Radioactive nuclei in the Universe provide a unique way to constrain stellar ages without relying on stellar evolution models. Thorium and Uranium are of astrophysical interest because their most stable isotopes, Th 232 and U 238, have half-life times of 14 and 4.5 billion years, respectively. HRMOS will provide high-resolution spectra that will enable measurements of Th abundances, and its multiplexing capability will allow observations for an unprecedented number of stars. In this talk, I will present a feasibility study for using HRMOS to measure Th abundances and introduce science cases it can address, such as constraining the age of the Universe from old stars.