Additional updates at the end.
From The Guardian:
The UN's nuclear watchdog has asked Iran to explain evidence suggesting that Iranian scientists have experimented with an advanced nuclear warhead design, the Guardian has learned.Do you hear that silence?
The very existence of the technology, known as a "two-point implosion" device, is officially secret in both the US and Britain, but according to previously unpublished documentation in a dossier compiled by the International Atomic Energy Agency (IAEA), Iranian scientists may have tested high-explosive components of the design. The development was today described by nuclear experts as "breathtaking" and has added urgency to the effort to find a diplomatic solution to the Iranian nuclear crisis.
The sophisticated technology, once mastered, allows for the production of smaller and simpler warheads than older models. It reduces the diameter of a warhead and makes it easier to put a nuclear warhead on a missile.
Documentation referring to experiments testing a two-point detonation design are part of the evidence of nuclear weaponisation gathered by the IAEA and presented to Iran for its response.
The dossier, titled "Possible Military Dimensions of Iran's Nuclear Program", is drawn in part from reports submitted to it by western intelligence agencies.
The agency has in the past treated such reports with scepticism, particularly after the Iraq war. But its director general, Mohamed ElBaradei, has said the evidence of Iranian weaponisation "appears to have been derived from multiple sources over different periods of time, appears to be generally consistent, and is sufficiently comprehensive and detailed that it needs to be addressed by Iran".
Extracts from the dossier have been published previously, but it was not previously known that it included documentation on such an advanced warhead. "It is breathtaking that Iran could be working on this sort of material," said a European government adviser on nuclear issues.
James Acton, a British nuclear weapons expert at the Carnegie Endowment for International Peace, said: "It's remarkable that, before perfecting step one, they are going straight to step four or five ... To start with more sophisticated designs speaks of level of technical ambition that is surprising."
Iran has rejected most of the IAEA material on weaponisation as forgeries, but has admitted carrying out tests on multiple high-explosive detonations synchronised to within a microsecond. Tehran has told the agency that there is a civilian application for such tests, but has so far not provided any evidence for them.
Western weapons experts say there are no such civilian applications, but the use of co-ordinated detonations in nuclear warheads is well known. They compress the fissile core, or pit, of the warhead until it reaches critical mass.
That is the sound of Western governments leaping into action to stop what is very obviously Iran's relentless drive to build not only nuclear weapons but also their delivery systems. Which could, by the way, reach most of Europe.
But taking military action to stop the inevitable deployment of weapons that can kill millions would be immoral and wrong. Much better to use diplomacy. It's worked so well so far, after all.
UPDATE: Raymond in DC, in the comments, adds:
"Two point implosion" implies a plutonium core, not one based on enriched uranium. This confirms a long-held suspicion of a two-track development project in Iran. While attention has focused on Natanz and those spinning centrifuges, work on the heavy water facility in Arak and the effort to extract plutonium from spent reactor fuel has not gotten the attention it deserved.
We should recall that the Syrian nuclear plant destroyed by Israel in 2007 was based on a North Korean design intended to produce plutonium. (It was reportedly funded by Iran.)
UPDATE 3: Grazi in the comments brings us three important links:
An interview with former IAEA inspector,
That same inspector's article about how Syria needs to be checked out more carefully, and
Joshua Pollack on Iranian/North Korean cooperation.