In 1912 many physicians considered radium a cure for cancer but few could afford it because radium cost a fortune. William Duane, Marie Curie's associate, discovered that “radium milk” (later officially named radon) was easier for physicians to use. In 1915 he built Boston's first radium “cow” and thousands of patients were treated with its “milk.” But because radon decayed with high‐energy alpha emissions, it also became the first “atom smasher.” Making radon available to nuclear scientists was one of America's major contributions to an evolving nuclear age.