"Радіоактивних" refers to materials that emit radiation due to the decay of unstable atomic nuclei. This process can release particles and energy, which can be harmful to living organisms. Common examples of radioactive materials include elements like уран and плутоній. Radioactive substances are used in various fields, including medicine, where they help in diagnosing and treating diseases, such as cancer. Additionally, they play a role in energy production through nuclear reactors, which harness the energy released during radioactive decay to generate electricity.