For example, at over 1. 9 years, over a billion times longer than the current estimated age of the universe, bismuth-209 ( atomic number 83 ) has the longest known alpha decay half-life of any naturally occurring element.

For example, at over 1. 9 years, over a billion times longer than the current estimated age of the universe, bismuth-209 ( atomic number 83 ) has the longest known alpha decay half-life of any naturally occurring element.

0.004 seconds.