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Why does uranium-235 hexafluoride collect nearer the center of a spinning centrifuge?

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Enrichment of uranium — uranium processing How uranium is enriched to make a nuclear weapon.

In a gas centrifuge used for uranium processing, the separation of isotopes occurs because of the relative centripetal forces experienced by the molecules.12

When the uranium hexafluoride (UF $_{6}$ ) gas is spun at extremely high speeds, the heavier molecules—specifically those containing the isotope $^{238}$ U—are pushed outward by these forces and accumulate along the outer walls of the centrifuge. Because the $^{235}$ UF $_{6}$ molecules are lighter, they are less affected by the outward force and consequently tend to concentrate near the center (or axis) of the spinning centrifuge, where they can then be siphoned off.123