[填空题]
The two isotopes of urdv 1uj-zubm5 2aniumar-8hp j7d l, v5qn(kmrybw4z5u :o9v, $^{235}$U and $^{238}$U (the superscripts refer to their atomic mass), can be separated by a gas-diffusion process by combining them with fluorine to make the gaseous compound UF$_6$ Calculate the ratio of the rms speeds of these molecules for the two isotopes, at constant T.