Australia’s nuclear safety agency said on Tuesday it had joined the hunt for a tiny radioactive capsule missing somewhere in the outback, sending a team with specialized car-mounted and portable detection equipment.

Authorities have now been on a weeklong search for the capsule, which is believed to have fallen from a truck that made a 870-mile journey in Western Australia. The loss has triggered a radiation alert for large parts of the vast state.

The capsule, part of a gauge used to measure the density of iron ore feed, had been entrusted by Rio Tinto Ltd to a specialist contractor to transport. Rio apologized on Monday for the loss, which happened sometime in the past two weeks.

The Australian Radiation Protection and Nuclear Safety Agency said it was working with the Western Australian government to locate the capsule. It added that the Australian Nuclear Science and Technology Organisation has also sent radiation services specialists as well as detection and imaging equipment.

The truck travelled from Rio’s Gudai-Darri mine, north of Newman, a small town in the remote Kimberley region, to a storage facility in the suburbs of Perth — a distance longer than the length of Great Britain.

State emergency officials on Tuesday issued a fresh alert to motorists along Australia’s longest highway to take care when approaching the search parties, as vehicles carrying the radiation detectors are travelling at slow speeds.