The Manhattan Project: Making the Atomic Bomb

Part II: Early Government Support

Liquid Thermal Diffusion

The Uranium Committee briefly demonstrated an interest in a fourth enrichment process during 1940, only to conclude that it would not be worth pursuing. This process, liquid thermal diffusion, was being investigated by Philip Abelson at the Carnegie Institution. Into the space between two concentric vertical pipes Abelson placed pressurized liquid uranium hexafluoride. With the outer wall cooled by a circulating water jacket and the inner heated by high-pressure steam, the lighter isotope tended to concentrate near the hot wall and the heavier near the cold. Convection would in time carry the lighter isotope to the top of the column. Taller columns would produce more separation. Like other enrichment methods, liquid thermal diffusion was at an early stage of development. 11

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