PRlMITlVE, INEFFICIENT, BUT MAY DO THE JOB

This cannot be done chemically, since isotopes such as U 238 and U 235 have identical chemical properties and differ only in atomic weight. It must be done by a physical process, which always starts with converting the uranium to a gas, uranium hexafluoride. In the Manhattan Project, the enrichment was performed by dif-fusion, using the different rates at which the two isotopes would seep through membranes in many stages. This method is now out-dated (although still used in the US in the old plants) and has been superseded by centrifuges, separating the two isotopes by much the same principle as in those separating cream from milk. To produce even one small uranium bomb in a reasonable time, Sad-dam would need some 1,000 of these highly sophisticated centrifuges. Normally they work in cascades, and would therefore require a large plant that could not easily escape detection.

But Saddam has put entire airfields underground, so this is not a fatal objection. Another possibility is that the Soviet army supplies the uranium; even before Gorbachev became a dictator, whether on his own or as a KGB tool, he was clearly not in firm control of the armed forces, and Stalinist Soviet army or KGB generals could easily have done so with impunity.

Most likely, however, he is using a West German/ South African patent which also uses centrifugal force for separation, but not by a centrifuge. Instead, the gas goes through a jet at high velocity and then through curved channels in which the centrifugal force acts on the isotopes as they go through them. The channels go round a circle, with the curves deviating from it alternately inside and out-side the circumference in wavy fashion, resulting in an alternately outward and inward radial centrifugal force on the gas as it speeds through this path.

The method is primitive and inefficient, but a country like Iraq does not need any sophistication, and the inefficiency merely means more time, more equipment and more money, of which dic-tators usually have plenty. The jets would have to work in cascades, so that they would be put underground. Conceivably the gas could be shipped or piped from one place of several stages to another with the next several stages. But even if in one place, this seems a plausible method to me.