A lump of deadly caesium-137 went missing in the Australian outback. — It’s 1987, and Rick Astley’s “Never Gonna Give You Up” is blaring on the radio for the first time, but miles away in Goiânia, Brazil, something horrific is taking place. Local scrap merchants had discovered 93 grams of a strange powdery material that glowed blue in the dark. Amazed by…