He coins the terms alpha and beta rays in 1899 to describe the two distinct types of radiation emitted by thorium and uranium salts. Rutherford is joined at McGill University in 1900 by Frederick Soddy and together they discover nuclear transmutation when they find in 1902 that radioactive thorium is converting itself into radium through a process of nuclear decay and a gas (later found to be 4 2He ); they report their interpretation of radioactivity in 1903.[8] Rutherford becomes known as the "father of nuclear physics" with his nuclear atom model of 1911.[9]