TEHRAN -- International Atomic Energy Agency inspectors have discovered that Iran produced and experimented with polonium, an element useful in initiating the chain reaction that produces a nuclear explosion, according to two individuals familiar with a report the inspectors will submit to the United Nations this week.
Iran reportedly acknowledged the experiments but offered an explanation involving another of polonium's other possible uses, which include power generation. The agency noted the explanation and left the issue "hanging there," said one person familiar with the matter. The experiments were described by that person as occurring "some time ago."
The discovery is the latest example of a nuclear activity that Iran had not previously disclosed. Earlier, it was revealed that Iran had obtained plans and parts for a nuclear centrifuge, a sophisticated machine used to enrich uranium for use in power plants, as well as in nuclear weapons. Iran insists it always intended its nuclear program to be used only to supply electrical power.
Polonium is a radioactive, silvery-gray or black metallic element. The most common natural isotope is polonium-210. It has some industrial purposes, but can also be utilized, in combination with beryllium, to make sure that the chain reaction leading to a nuclear explosion is initiated at precisely the right moment.
"It does heighten suspicions because polonium-210 is so linked to a certain type of neutron-initiator," said David Albright, a specialist on nuclear proliferation at the Institute for Science and International Security. "But it's not an ideal neutron-initiator. It doesn't last long, so you've got to keep producing it."
Polonium-210 has a half-life of 138 days. Specialists say research on polonium would be done early in a weapons program. "It's quite clear they were trying to make an explosive device," said one person with knowledge of the polonium discovery. "But they hadn't gotten far enough. No one will find a smoking gun because they weren't able to make a gun."
The disclosures present an unwelcome political challenge for Iran, which was hoping to put the nuclear issue behind it before March 8, when the full board of the International Atomic Energy Agency convenes in Vienna. Instead, diplomats said, Iranian officials were bracing for a report raising enough questions to keep the nuclear issue alive.
"They are going to be facing this problem for a while," said one diplomat.
"We remain committed to our obligations under the International Atomic Energy Agency," Foreign Ministry spokesman Hamid Reza Asefi said on Sunday, while acknowledging that Iran had acquired nuclear equipment from "middlemen" representing a Pakistani nuclear scientist. "We've never pursued nuclear arms and will never do so," he said.
Iran is undergoing fresh inspections by the atomic agency, the UN body charged with enforcing the 1970 nuclear Non-Proliferation Treaty. Iran was facing a deadline for disclosing its nuclear activities late last year when three European countries persuaded its government to accede to international pressure to open its nuclear program. Iran agreed to permit more rigorous inspections, suspend uranium enrichment, and make a full accounting of nuclear programs it had kept largely secret for 18 years.
Inspections appear to have gone smoothly. Iran's state-controlled media make no mention of the presence of the foreign inspectors. And though one foreign official said the atomic agency would prefer that Iranian officials be "more proactive" in revealing previously hidden elements, Iranian officials have made no effort to block the inspectors.
On the other hand, their discoveries corrode Iran's already fragile credibility. Neither the polonium work nor plans for a P-2 centrifuge were mentioned in Iran's earlier "comprehensive" summary. Discovery of the P-2 centrifuge design and components -- revealed after Libya exposed a black market in nuclear programs run out of Pakistan -- was especially damaging to trust, officials said.
"They say it was an oversight. The IAEA people don't think it was an oversight," said one analyst here. "You have forces that want to keep things secret."
Albright, who has written extensively on Iran's nuclear program, said, "The Libyan bomb design looks like what China gave Pakistan, and why wouldn't have Iran gotten it?
"There's a lot of pressure on Iran," he said. "And I don't think it's credible that Iran says it never had a military nuclear program. To me, it's not so much a suspicion, it's more of an assessment that Iran did have a nuclear weapons program."
Privately, many foreign and Iranian analysts agree. "The intention is clear from the fact they had a clandestine program," said one analyst, who would not be identified by nationality or position.