11 June

People have been plundering warship wrecks from WW2. You’ll never guess why. They’re after the rarest metal in the world. It’s actually just steel, but a special type of steel, it’s called ‘low background steel’. Making steel uses a lot of oxygen, they ‘blast’ the furnaces with air (why they’re called blast furnaces, funnily enough). But from 1945 onwards, the US and Russia in particular started doing thousands of open-air nuclear explosions. So any steel made post-1945 has radioactive air particles included in the steel. This doesn’t matter for most uses, but for some, like building radiation detectors, it’s crucial that the steel is radiation-free. That’s why the wrecks are being plundered, for steel made before nuclear tests began. The level of radioactive particles now in the air from those tests is almost zero, so it’s not clear this plundering actually needs to happen.