Update: A passerby in a town south of Basra, Iraq, found the missing radioactive iridium. [Read more on the finding]
Some security experts are worried that a cache of radioactive material reportedly stolen from an oil field in Iraq could be used by organizations such as the Islamic State group to produce a dirty bomb.
A laptop-size case with about 0.35 ounces (10 grams) of the material, called iridium-192, allegedly went missing from an oil field storage facility in Basra that is run by the American company Weatherford, Reuters reported. Both the company and the Iraqi government declined to confirm the report.
"We are afraid the radioactive element will fall into the hands of Daesh," a senior security official with the Iraqi government, told Reuters, using an Arabic acronym for the Islamic State group, also called ISIS. "They could simply attach it to explosives to make a dirty bomb." [Doomsday: 9 Real Ways Earth Could End]
So, what is iridium-192, and could it really be used in a dirty bomb?
Based on reports of what was allegedly stolen, "you will not make a dirty bomb that has much of an actual health risk, because there's so little material," said Robert Rosner, former director of Argonne National Laboratory and a professor of physics and astronomy at the University of Chicago. "But you can scare the bejesus out of people."
Iridium is the 77th element on the periodic table, and is a very dense, platinumlike metal that is highly resistant to corrosion. It is often recovered as a byproduct of nickel mining, and is used in electrical connections and to harden platinum.
Iridium-192 is a radioactive isotope, meaning it's a version of iridium with a different number of neutrons than is contained in the dominant forms of the element. Iridium-192 does not typically occur naturally. Instead, scientists must put iridium-191 in a nuclear reactor and bombard it with neutrons. The iridium-191 then takes up an extra neutron to become iridium-192.
However, the iridium-192 is unstable and emits electrons and gamma-rays (highly energetic packets of light) to decay into osmium isotopes and platinum isotopes. The half-life of iridium-192 is about 74 days, meaning that in that space of time, half of the material will have decayed to more stable forms, Rosner said.
The International Atomic Energy Agency defines iridium-192 as a category-2 radioactive substance. This means the substance can permanently injure a person who handles the radioactive material for minutes to hours, and it can kill people in close proximity within hours to days, according to the agency.
The high-energy gamma-rays do their damage directly in the short term.
"You actually get irradiation burns, tissue damage and necrosis [tissue death]," Rosner said.
However, that acute form of radiation sickness would mainly occur if someone were to open up the case or hold the unshielded capsules in his or her hands.
Longer-term damage, such as cancer, would occur only if the cells in the body absorbed the radioactive material, which would then continue to emit DNA-damaging gamma-rays over a long period, Rosner said. However, the body doesn't normally use iridium for biological processes, so such damage is less likely than with other radioactive substances, such as radioactive iodine, Rosner added. One 2008 case study found that a man exposed to a high dose of iridium-192 who was followed over 20 years did not develop some of the longer-term radiation illness found with other types of radioactive substances.
The oil field in Basra likely was using iridium-192 to image the inside of its pipelines, Rosner said. Pipelines are typically made of dense materials that X-rays can't adequately penetrate, so instead, oil companies use more energetic gamma-rays to peer inside the massive pipes. The iridium source is usually placed inside the pipelines, and a detector outside the pipe tracks the amount of gamma radiation, which reveals if the walls of the pipeline are thicker or thinner, or if there is a crack, Rosner said.
Iridium-192 is also often used in radiation therapy. For instance, in a technique called Gamma Knife surgery, a focused beam of gamma-rays is used to directly cut or destroy tumor cells, Rosner added.
Risk of dirty bomb or nuclear terrorism
It's still not clear whether the material really was stolen or simply lost. Even if the material was stolen by bad actors such as the Islamic State group, the actual risk of mass casualties is small, Rosner said.
"The amount of people hurt by being exposed to this stuff is not going to be very different from the number of people who are hurt by any bomb going off," Rosner told Live Science.
For one, a dirty bomb would disperse the material out over an area dozens of feet in diameter, diluting the effects. Moreover, the first rainstorm would wash away much of the substance, and what was left in the environment would quickly decay naturally.
Nonetheless, a dirty bomb could incite terror, Rosner noted.
"If you spread the material over a fairly large area, the effect is relatively modest, but the psychological effects are huge," Rosner said. "People are scared of radioactive materials."
This isn't the first time that the radioactive material has been stolen. In 2011, a car thief stole a medical camera that contained iridium-192 from the parking lot of a Texas hotel. The material was never recovered.
And in 2013, carjackers in Mexico unwittingly stole cobalt-60 — a dangerous radioactive isotope used in both medical therapies and food irradiation — from a truck fitted with a radiotherapy machine used for cancer treatment. While the material was eventually recovered, the event highlighted the danger that could result from unsecured sources of radiation.
"Perhaps the most worrisome lesson of the Mexican incident and the other ones above is this: If hapless truckjackers can steal high-activity sources by accident, a well-organized terrorist group could certainly do so in a planned operation," scientists at the Bulletin wrote at the time.