By Lewis Jackson

SYDNEY (Reuters) – A lost radioactive capsule found after a search along a 1,400 km stretch of the arid Western Australian outback is due to arrive in Perth on Thursday evening as investigators work on piecing together just how it fell from a truck.

The capsule – 6mm in diameter and 8 mm long or about the size of a tic-tac sweet – was found in the state’s remote northwest on Wednesday. The week-long search retracing the truck’s journey involved 100 people from at least five government agencies using specialised radiation detection equipment.

Verified by members of Australia’s Defence Force and sealed in a lead container, the Caesium-137 capsule is being escorted to Perth by a team of 14 that includes nuclear specialists. It will be stored at a facility that officials declined to identify, citing security reasons.

A search team found it when Australian-invented CORIS360 radiation equipment mounted to their car driving along the Great Northern Highway detected gamma rays 74 km south of the town Newman in the state’s Kimberley region.

“Everything spiked and the computers went mad and they hit the brakes and flew out of the vehicle in excitement,” Department of Fire and Emergency Services Incident Controller Darryl Ray told a news conference on Thursday.

GRAPHIC: Australia’s missing radioactive capsule found (https://www.reuters.com/graphics/AUSTRALIA-RADIATION/zdvxdnrmrvx/graphic.jpg)

The team then deployed portable detection equipment, locating the capsule at 11:13 am local time (0313 GMT) on Wednesday, about 2 metres from the side of the road.

No one is thought to have been exposed to radiation and the site was not permanently contaminated, officials said.

Prime Minister Anthony Albanese lauded its recovery.

“Little radioactive, tiny little thing that they were looking for like a needle in a haystack. But they found it to their great credit, though,” he told a Perth radio station.

The capsule was part of a gauge used at Rio Tinto’s Gudai-Darri iron ore mine. Authorities believe the gauge broke apart on the journey, dislodging the capsule which then fell out of its crate and from the truck, a road train with multiple trailers.

Western Australia’s Chief Health Officer Andrew Robertson told reporters on Thursday the investigation would look at how the gauge was made, operated, packaged and transported.

Prosecutions would be considered under state radiation safety laws dating to 1975. A report for Western Australia’s Health Minister is due in several weeks.

The maximum penalty for failing to safely handle radioactive substances is A$1,000 and A$50 per day the offence continues, though the state government has flagged new rules with bigger penalties.

Officials said any changes would not be retrospective.

Rio Tinto has launched its own investigation and has offered to reimburse the cost of the search. It has also said it will cooperate fully with the official investigation.

Subcontractors SGS Australia, responsible for the packaging of the gauge, and Centurion, responsible for its transportation have also said they will cooperate.

(Reporting by Lewis Jackson; Editing by Edwina Gibbs)

---