Radioactive material
Around 10g of the radioactive isotope Iridium-192 is missing in IraqGetty

Radioactive material has been declared stolen from an oil depot in Iraq, sparking fears among officials it could be used as a weapon if seized by Islamic State. The "highly dangerous" Iridium-192, which was stored in a protective case the size of a laptop, went missing from a storage facility belonging to a US oilfield company in the southern city of Basra.

A senior environment ministry official told Reuters up to 10g of Iridium-192 in capsules could not be traced. The substance itself is the property of Istanbul-based SGS Turkey.

What is Iridium-192 and what is it used for?

The material is a radioactive isotope of the element iridium, which has a shelf-life of 73.83 days and emits beta and gamma radiation as it decays. Iridium is a silvery-white metal and is roughly twice as dense as lead. Unlike the more stable isotopes Iridium-191 and Iridium-193, Iridium-192 does not occur in nature.

It is used as a gamma ray source in industrial radiography to test for flaws in metal components, such as oil and gas pipelines. It is also used as a radiation source in radiotherapy, particularly brachytherapy which is commonly used to treat cervical, prostate, breast and skin cancer.

Why is it dangerous?

The material is a Category 2 radioactive source according to the International Atomic Energy Agency. Iridium-192 can be fatal if someone is exposed to it for a period of hours to days without the material being handled properly. It can cause permanent damage in a matter of minutes. Exposure to the substance can lead to burns, radiation poisoning, acute radiation sickness and ultimately death.

Security officials fear the stolen Iridium-192 could be used to make a "dirty bomb", which is a radiological weapon that combines radioactive material with conventional explosives. Such a weapon can be used to contaminate an area with radioactive material rendering the vicinity hazardous.

However, there is no indication the material had come into the possession of Isis. Although the jihadist group announced the establishment of a "caliphate" stretching from Aleppo in Syria to Diyala Province in Iraq, it does not control areas near Basra where the Iridium-192 went missing.

Has any Iridium-192 gone missing before?

Yes, quantities have gone missing in the United States, the UK and other countries. In February 2013, a cannister of Iridium-192 was stolen from a van in Bacup, Lancashire.

In 2014, a man in China fell ill after taking home some Iridium-192 from his job at the Fifth Construction Co, a subsidiary of China's oil refinery operator Sinopec, in Nanjing. Last year, Mexican authorities issued an alert covering five states after a container of Iridium-192 used for industrial radiography was taken from a truck in the town of Cardenas in Tabasco state.