Where did the highly enriched uranium (HEU) particles come from?
Iranian officials asserted that highly enriched uranium (HEU) particles found at the Natanz pilot plant in 2003 came from contamination from foreign-origin centrifuge assemblies, which was the first clue revealing the Pakistani A.Q. Khan network as supplier of some centrifuges to Iran. Iran admitted to enriching uranium to just 1.2%, while the particles sampled ranged from 36% U-235 to 70% U-235 enrichment. In October 2003, Iranian officials admitted they tested centrifuges at the Kalaye Electric Company using UF6 between 1998 and 2002. The IAEA did not rule out the possibility that Iran’s own enrichment activities could be the source of the HEU in samples. Why did Iran keep other information hidden? Iran has been particularly slow to reveal the existence of more sophisticated centrifuge designs (using maraging steel or composite rotors) and its laser enrichment program. Iran provided significant detail about the P-1 centrifuges in its October 2003 declaration, but it did not admit unt
