Uranium- 235 can be separated from U-238 by fluorinating the uranium to form $\mathrm{UF}_{6}$ (which is a gas) and then taking advantage of the different rates of effusion and diffusion for compounds containing the two isotopes. Calculate the ratio of effusion rates for ${ }^{238} \mathrm{UF}_{6}$ and ${ }^{235} \mathrm{UF}_{6}$. The atomic mass of U-235 is $235.054 \mathrm{amu}$ and that of $\mathrm{U}-238$ is $238.051$ amu.