A tiny capsule of radioactive matter that sparked a nuclear safety warning has been found in the middle of the Australian outback after a weeklong search that was like looking for a "needle in a haystack".
The solid, silver-coloured cylinder is smaller than a human fingernail - just eight millimetres by six millimetres - but the authorities say it contains enough Caesium-137 to cause acute radiation sickness.
It disappeared sometime after Jan 10 on a desert road stretching some 1,400 kilometres (870 miles) - the longest and most remote highway in the world.
Nuclear scientists travelled to the state of Western Australia to begin the painstaking task of searching between the state's capital, Perth, and the remote Kimberley region – a distance equivalent to driving between London and Edinburgh then back again.
Announcing the discovery on Wednesday, Stephen Dawson, the emergency services minister for Western Australia, said searchers "have quite literally found the needle in the haystack".
"I do want to emphasise this is an extraordinary result," Mr Dawson said. "Western Australians can sleep better tonight."
Detection devices attached to a vehicle picked up signs of radiation waves on Wednesday morning south of the Pilbara town of Newman, about two metres from the edge of the Great Northern Highway.
Dr Andrew Robertson, the chief health officer of Western Australia, said the "tiny source" had posed a "significant" health risk.
It did not look like it had been moved since landing near the highway and it would be "extremely" unlikely radioactive material had leaked in the area, he added.
Army experts were being called in on Wednesday to inspect the capsule and verify that it was the missing piece.
Mining giant Rio Tinto had admitted on Jan 25 – the eve of a public holiday when millions of Australians hit the road – that one of their contractors lost the caesium-137 capsule.
The small part, from a gauge used to measure the density of iron ore, was believed to have fallen off the back of a truck some time between Jan 11 and Jan 16 while it was being driven from Rio Tinto's Gudai-Darri mine to a city storage facility.
When workers unpacked the package for inspection, the gauge was found broken apart, with one of four mounting bolts missing and screws from the gauge also gone.
Simon Trott, Rio Tinto's chief executive, said the company was “incredibly grateful" but "the fact is it should never have been lost in the first place".
"I’d like to apologise to the wider community of Western Australia for the concern it has generated," Mr Trott said.
"We are taking this incident very seriously and are undertaking a full and thorough investigation into how it happened.
"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 contractors who lost the capsule are under investigation and may face prosecution.
Rio Tinto was at the centre of controversy in the Pilbara region, and across Australia, two years ago when it emerged the company had blown up a sacred Aboriginal site.