Send any friend a storyThe United States is wiring Ukraine with sensors that can detect‌‌ bursts of radiation from a nuclear weapon or a dirty bomb and can confirm the identity of the attacker. The preparations, mentioned last month in a House hearing and detailed Wednesday by the National Nuclear Security Administration, a federal agency that is part of the Energy Department, seem to constitute the hardest evidence to date that Washington is taking concrete steps to prepare for the worst possible outcomes of the invasion of Ukraine, Europe’s second largest nation. “If they wanted to render as much of the countryside as they could uninhabitable, those reactors might become targets