Radium is a ignoble metal, which chemically is very similar to barium. It is radioactive, the most stable isotope, 226Ra, has a half-life of 1602 years and decays to radon. Radium was discovered by Marie Curie and played an important role in the earliest research of radioactivity. Up to the late 1920s, it was treated quite unscrupulously and was even promoted as being healthy. A popular application was for self-luminous paint in clock dials until the 1960s. Only after many people died very gruesome and slowly, it was realized that radioactivity isn't harmless at all, but very tissue-damaging. Today radium is hardly used for anything, except in very small amounts for research. Natural radium is produced in the decay chain of uranium via thorium.