In the Iranian desert, at a sprawling industrial site ringed by barbed wire and antiaircraft guns, a shift in the enrichment of uranium is producing global jitters because it could shorten Iran’s path to the acquisition of nuclear weapons.  It is also illustrating one of the peculiarities of uranium enrichment, a version of the rich getting richer, really fast. The tricky process accelerates as it moves ahead. “The higher the concentration, the easier it gets,” said Houston G. Wood III, a professor of mechanical and aerospace engineering at the University of Virginia who specializes in nuclear enrichment. The process is, as scientists like to say, nonlinear…A practical illustration of nonlinearity is that Iran — or any other nuclear hopeful — needs increasingly few centrifuges to make uranium 235 increasingly potent. For instance, one industry blueprint features 3,936 centrifuges for enriching up to 4 percent, 1,312 centrifuges to 20 percent, 546 centrifuges to 60 percent and just 128 centrifuges to 90 percent — the level needed for a bomb. The reason is that “you’re moving a lot more material at lower levels of enrichment,” said David Albright, president of the Institute for Science and International Security, a private group in Washington that tracks nuclear proliferation and disclosed the blueprint. “It’s the reduction of the material” that makes the process gradually easier. – New York Times