European authorities are providing new details about a cloud of mysterious radioactive material that appeared over the continent last month. Monitors in Italy were among first to detect the radioactive isotope ruthenium-106 on Oct. 3, according to a fresh report by France's Radioprotection and Nuclear Safety Institute, known as IRSN. In total, 28 European countries saw the radioactive cloud, the report says. The multinational Comprehensive Nuclear-Test-Ban Treaty Organisation, which runs a network designed to monitor for nuclear weapons tests, also confirmed to NPR that it had detected the cloud. Based on the detection from monitoring stations and meteorological data, the...