What is the radioactive capsule missing in WA used for and how dangerous is it?

As authorities scour the desert for the missing source, here's what we know about how it works and what threat it poses to humans

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Authorities are continuing the search for a tiny radioactive capsule lost along a 1,400km stretch of Western Australian desert highway.

The 8mm by 6mm capsule fell from a secure device on a truck that was travelling from a Rio Tinto mine site, north of Newman in the Pilbara region, to Perth, where it was being sent for repair.

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