The Manhattan Project: Making the Atomic Bomb

The Electromagnetic Method

The electromagnetic method, pioneered by Alfred O. Nier of the University of Minnesota, used a mass spectrometer, or spectrograph, to send a stream of charged particles through a magnetic field. Atoms of the lighter isotope would be deflected more by the magnetic field than those of the heavier isotope, resulting in two streams that could then be collected in different receivers. The electromagnetic method as it existed in 1940, however, would have taken far too long to separate quantities sufficient to be useful in the current war. In fact, twenty-seven thousand years would have been required for a single spectrometer to separate one gram of uranium-235.⁹

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