The method studied by the Berkeley investigators was evolved by the German scientists Messrs. Clusius and Dickel, primarily to separate isotopes, the slightly different kinds of atoms which make up many of the so-called pure elements. The process is called thermal diffusion. It utilizes heat to part the different kinds of atoms.
An atom of uranium has a weight of 238, which means it is approximately that many times as heavy as a hydrogen atom. But scattered among the atoms of ordinary uranium are atoms with a weight of 235. They are the ones that are self-disintegrating and therefore capable of emitting these enormous amounts of energy without help.
This uranium isotope, variously called U 235 and actinouranium, constitutes less than 1 per cent. of ordinary uranium. When the two kinds are together in their natural state the U 235 ig not self-exploding. Uranium 238 is capable of producing great power by explosion, hut requires an outside source of energy as a detonator. Hence the necessity for separation to get quantities of the self-disintegrating kind.
Some experimenters have tried the ultracentrifuge, which effectively separates many Ordinary substances made up of tiny particles of different weights. Others have obtained small quantities, getting less than 1,000,000th of a gram, by shooting uranium atoms through a magnetic field. The U 235 atoms, being slightly lighter than their brothers, travel through this field in a path different from the J 238 and thus can be isolated.
The experimenters said atomic power research apparently is being carried on secretly in some places, since it is known that much work is being done, yet little is being published sclentitically about it.
But when and if anyone does produce U 235 in quantity he will have to use extreme care in handling it, the Berkeley (California) men said, because of the damage which might result from an uncontrolled explosion.
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