Ears prick up around the world at any news involving radioactivity and Iran. The most recent story broke on Friday, when Russia's customs service announced that it had stopped an Iranian man bound for the Iranian capital, Tehran, with 18 pieces of radioactive metal packed in steel pencil cases in his luggage. The material had triggered radiation detectors at Moscow's Sheremetyevo airport.
What was the radioactive material in the man's luggage and what is it normally used for?
It was sodium-22, an isotope used to make internal organs and tumours show up in medical PET scanners, and also to determine the thickness of metals and calibrate radiation measurements.
Was it part of a plot to make a bomb?
Unlikely. Mark Hibbs, a non-proliferation expert with the Carnegie Endowment for International Peace, a think tank based in California, says he discussed the incident on Saturday with "extremely senior" security staff at the White House. "The talks convinced me the sodium had no weapons use whatsoever", he says. "If it had been for weapons, we wouldn't have found out about it."
The material would be little use for a dirty bomb aimed at scattering radioactive contamination, as its emissions die fairly quickly, with a half-life of 2.6 years.
But is Iran trying to make a bomb all the same?
The Iranian government denies it – but it probably could it if wanted to. Both inreports last month and in unpublished assessments, the International Atomic Energy Agency (IAEA) says Iran has the know-how and enough fuel-grade uranium to make four nuclear bombs, if it enriches the uranium further. It has already enriched 80 kilograms of it to one step short of weapons grade.
Why would Iran need sodium-22, then?
Probably for medical use. The Tehran Research Reactor, where Iran makes its own medical isotopes, is out of fuel, and although Iran says it will soon make its own, "the production line isn't working yet", says David Albright of the Institute for Science and International Security, a think tank in Washington DC that watches Iran.
Why was the man taking it out of Russia in his luggage?
"Iran is a magnet for isotopes dealers, and Russia is a major supplier," says Hibbs.
Sodium-22 can be imported into Iran legally because of its medical uses, he says. The man might simply have been dodging the costly export permit.
The incident happened a month ago, and the Iranian, a dental student, was released after what the Iranian ambassador to Moscow called "a misunderstanding" – although apparently without his radioactive stuff.
How did it get through?
The real question raised by the incident is how much radioactive material like this breezes unimpeded through airports less vigilant, or well-equipped, than Moscow's. There's enough of it about: in September the IAEA reported 172 incidents of radioactive material going astray just in the past year, including 46 attempts to steal, smuggle or sell it, and 10 where it wasn't recovered.
Sixteen incidents involved the plutonium or highly enriched uranium that can be used to make bombs. Last year in Washington DC governments agreed to take better care of their stocks – but the agreement lacked teeth.
How was it detected?
Moscow would have spotted the sodium-22, which emits gamma rays, with a detector similar to a Geiger counter, says Hibbs. These were installed in several Russian airports by a US-Russian programme in the 1990s to lock down nuclear material after the fall of the Soviet Union. But they aren't routine everywhere, says Jason Woods of Washington University in St Louis, Missouri, because "if you stopped everything with gamma rays, you'd hold up a lot of shipments".
For example, US airports scanned flights from Japan after the Fukushima nuclear accident this year and found gamma rays coming from cargo onflights to Chicago and Dallas. The source turned out to be ordinary medical equipment.
Moreover, "there are big holes in export controls worldwide", says Hibbs, especially outside the Nuclear Suppliers Group of 46 mostly rich countries.
What is being done to stop other forms of radioactive material being smuggled?
The IAEA is developing better handheld detectors to spot different kinds of radiation. Neutron detectors, meanwhile, can spot plutonium without being distracted by legitimate gamma emitters. The US wants to install them at land transport hubs, seaports and airports worldwide.
The problem, says Woods, is that current detectors use helium-3. "It's shy a neutron, so it's hungry for them and good at picking them up," he says. But US production of helium-3 is 8000 litres per year, and the detector programme needs 60,000. Last year Russia stopped exporting it.
Moreover, says Woods, helium-3 is irreplaceable for work in ultra-low-temperature physics and medical uses such as lung imaging. "It should be kept for that," he says, and told the US Congress so earlier this year. Congress agreed: the detector programme is on hold while equipment manufacturers develop alternatives based on boron-10.
