Inelastic cross sections for collisions between thorium (Th) and helium (3He) are measured. For Th[3𝐹2]–3He, we determine the ratio of momentum transfer to Zeeman relaxation cross sections to be 𝛾∼500 at 800 mK. For Th[3𝑃0 ]–3He, we find no quenching of this metastable state during $10^6$ collisions. We measure the radiative lifetime of Th[3𝑃0] to be 𝜏>130 ms. The observed stability of Th[3𝑃0] opens up the possibility of trapping this metastable species.