Uranium

Useless and Useful Uranium

The hardest part of making the atomic bomb was finding enough useful uranium to create a chain reaction. Only one in every five-hundred parts of uranium ore were even useable after being refined. And almost all of that uranium was Uranium-238, which was non-fissionable, making it completely useless in creating the atomic bomb. Only .72% of natural uranium was Uranium-235, the isotope needed to make the atomic bomb. To make things even harder, the useless and useful isotopes are almost identical in chemical makeup, making them very hard to separate. Only a machine would be able to do so.  

      Enriching the Uranium

Since only a machine could separate the two uranium isotopes, a massive enrichment plant was built in Oak Ridge, Tennessee. Harold Urey and his colleagues at Columbia University created an extraction system that worked on gaseous diffusion, but this only slightly separated the different uraniums. Ernest Lawrence provided a process that could magnetically separate the two isotopes. And to further separate them, a gas centrifuge was used. Once all these had been completed, the only thing left to do was test the concept of atomic fission (splitting the atom).

This picture is cited at http://www.atomicarchive.com/History/sites/Images/K_25.jpg

Magnetic Separation and Gaseous Diffusion

The electromagnetic method of separation used a mass spectrometer to send charged particles through a magnetic field. The Uranium-235 was deflected more by the magnetic field than the Uranium-238, causing the two isotopes to be collected separately. However, this was very costly and time-consuming. Since molecules of a lighter isotope travel more easily through a barrier full of pores than molecules of a heavier isotope, the gaseous diffusion method seemed a lot more promising. Uranium-235 and Uranium-238 could be easily separated out in cascades. However, even though it was much faster than the way of magnetic separation, gaseous diffusion was still extremely expensive.

Gas Centrifuge

The gas centrifuge process was the most efficient way of separating Uranium-238 and Uranium-235. It used a large number of rotating cylinders in long, parallel rows. When the cylinders rotated they created a strong centrifugal force, which caused the heavier Uranium-238 to move toward the outside of the cylinder and the lighter Uranium-235 to move in close to the center. The whole process achieved the same separation as gaseous diffusion and required much less energy.

This picture is cited at http://upload.wikimedia.org/wikipedia/commons/6/69/Gas_centrifuge_cascade.jpg