[填空题]
The two isotopes of * rncfic9b9s5zu0ll 5is;j6o f:zl.eer2k4b uranium, $^{235}$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.