A new report by the International Atomic Energy Agency (IAEA) suggests that Iran may have a programme to develop nuclear warheads capable of being deployed by missiles. The report is a little short on details, but it closely echoes a previous rumour from 2009 that suggested Iran was looking into how to build a compact weapon.

According to the IAEA, Iran has recently conducted work to develop a device that, when compressed by explosives, generates a large flux of neutrons. Such a neutron generator is the key to building a compact nuclear warhead that can be delivered by a missile instead of an aircraft. The agency says that the country has also been working with conventional high explosives that could be used to trigger a nuclear warhead, along with special systems used in nuclear testing. Taken together, it makes a compelling case that Iran’s nuclear intentions are not entirely peaceful.

The chief allegation is that Iran has conducted experiments with uranium deuteride, a material that, when compressed, creates a burst of neutrons. Neutrons are the key to starting a nuclear detonation. For compact bombs of the sort typically mounted on missiles, the neutrons needed to start the bomb have to come from an “initiator”. Uranium deuteride is an unconventional choice, but the Pakistani physicist and nuclear smuggler AQ Khan is suspected to have dabbled in it (see “Uran-deuteride” in the photo above). You can read more nuclear weapons nitty-gritty in our previous post.

The IAEA cites other reasons to be suspicious. The Iranians are apparently working with Exploding Bridgewire, a high speed explosive that could be used to compress a spherical nuclear bomb in order to set off its nuclear charge. They’re also studying ways to explode the bridgewire simultaneously, another important technique to ensure that a bomb compresses correctly. The Iranians have also acquired high-voltage firing equipment of the type you might use if you wanted to be very very far away from something when you pressed the button—say in a nuclear test. Finally, the Iranians are working on mounting a “spherical nuclear payload” onto their Shahab-3 missile.

The agency bases its report on “information which the Agency has acquired from Many Member States and through its own efforts”. It also says that its overall knowledge of Iran’s programme “continues to diminish”.