 Unlike the lower mass noble gases , the normal stellar nucleosynthesis process inside a star does not form xenon . Elements more massive than iron @-@ 56 have a net energy cost to produce through fusion , so there is no energy gain for a star when creating xenon . Instead , xenon is formed during supernova explosions , by the slow neutron capture process ( s @-@ process ) of red giant stars that have exhausted the hydrogen at their cores and entered the asymptotic giant branch , in classical nova explosions and from the radioactive decay of elements such as iodine , uranium and plutonium . 
