Radium-226 is a radioactive isotope of the element radium, which is found in trace amounts in uranium and thorium ores. It has a half-life of about 1,600 years, meaning it takes that long for half of a sample to decay. Radium-226 emits alpha particles and gamma radiation, making it hazardous to human health if ingested or inhaled. This isotope was historically used in luminous paints for watches and instrument dials due to its ability to glow in the dark. However, its use has been largely discontinued because of the serious health risks associated with radiation exposure, including cancer.