Bertram Borden Boltwood (27.07.1870-15.08.1927) was an American chemist and physicist and a member of the National Academy of Sciences (1911). He was born in Amherst. He graduated (1892) from the Sheffield Scientific School at Yale, and afterwards furthered his knowledge at the universities of Munich, Leipzig and Yale. At the last of these he worked from 1894 (in 1897 he received his doctorate there, and from 1910 he was professor).
His research concerned radioactivity and radiochemistry. He proved that radium and actinium are decay products of uranium, and that the last, non-radioactive product of the successive series of transformations of uranium is lead. Independently of O. Hahn he discovered (1907) ionium, which proved to be an isotope of thorium. He used radioactivity to determine the age of geological rocks.