 The only primordial isotope of bismuth , bismuth @-@ 209 , was traditionally regarded as the heaviest stable isotope , but it had long been suspected to be unstable on theoretical grounds . This was finally demonstrated in 2003 , when researchers at the Institut d <unk> <unk> in Orsay , France , measured the alpha emission half @-@ life of 209Bi to be 1 @.@ 9 × 1019 years , over a billion times longer than the current estimated age of the universe . Owing to its extraordinarily long half @-@ life , for all presently known medical and industrial applications , bismuth can be treated as if it is stable and nonradioactive . The radioactivity is of academic interest because bismuth is one of few elements whose radioactivity was suspected and theoretically predicted before being detected in the laboratory . Bismuth has the longest known alpha decay half @-@ life , although tellurium @-@ 128 has a double beta decay half @-@ life of over 2 @.@ 2 × 1024 years . 
