Uranium is a rather rare element, though known for over a hundred years, and has an atomic weight of 238.5.
"Q. E. D., or New Light on the Doctrine of Creation" by George McCready Price
In "The Secrets of the Bomb" Jeremy Bernstein writes that at the Manhattan Project at Oak Ridge, Tennessee, most of the separation of uranium-235 from uranium-238 was accomplished by means of electromagnetic fields.
For depleted-uranium, i.e., U-238, this gives a speci ﬁc act Ci/g which is listed in the last line of Table 1.
A comparison of delayed radiobiological effects of depleted-uranium munitions versus fourth-generation nuclear weapons
Natural uranium at the present time contains about 136 times as many atoms of the essentially non-fissionable 238U (pronounced U-238) as it does the readily-fissionable 235U.
Teaching About Nature's Nuclear Reactors