“We are incredibly grateful for the hard work of everyone involved in finding the missing capsule,” Rio Tinto Iron Ore CEO Simon Trott said. “While the recovery of the capsule is a great testament to the skill and tenacity of the search team, the fact is it should never have been lost in the first place.”

The round stainless steel capsule, which was smaller than a 9 mm bullet, contained Cesium-137. It was intended for use as a level sensor gauge on the iron ore feed for the mine’s crushing circuit. Packed by a specialist radioactive materials handler, the gauge was collected by a transport contractor from the Gudai- Darri mine site on January 10 and reported lost on January 25 when workers discovered the gauge had broken apart during transport.

“We are taking this incident very seriously and are undertaking a full and thorough investigation into how it happened,” Trott said. “This sort of incident is extremely rare in our industry, which is why we need to investigate it thoroughly and learn what we can to ensure it doesn’t happen again. As part of our investigation, we will be assessing whether our processes and protocols, including the use of specialist contractors to package and transport radioactive materials, are appropriate.”

The capsule was found south of Newman on the Great Northern Highway. Using portable search equipment, search crews detected radiation emissions and found the capsule lying 2 m off the highway. The search effort took seven days and spanned 1,400 km from Perth to the mine.