Uranium has two naturally occurring isotopes. 238U (atomic mass 238.0508 u) has a natural abundance of 99.275% and 235U (atomic mass 235.0439 u) has an abundance of 0.720%. The rarer isotope is needed for nuclear reactors. The isotopes are separated by forming uranium hexafluoride UF6, which is a gas, then allowing it to diffuse through a series of porous membranes. Since the speeds of these two isotopes are only slightly different, many repetitions of the diffusion pathways can be used to separate these isotopes. Given the atomic mass of fluorine is 18.9984 u, determine how many times faster the 235UF6 is than 238UF6.