 Naturally occurring xenon is made of eight stable isotopes , the most of any element with the exception of tin , which has ten . Xenon and tin are the only elements to have more than seven stable isotopes . The isotopes 124Xe and 134Xe are predicted to undergo double beta decay , but this has never been observed so they are considered to be stable . Besides these stable forms , there are over 40 unstable isotopes that have been studied . The longest lived of these isotopes is 136Xe , which has been observed to undergo double beta decay with a half @-@ life of 2 @.@ 11 × 1021 yr . 129Xe is produced by beta decay of 129I , which has a half @-@ life of 16 million years , while 131mXe , 133Xe , 133mXe , and 135Xe are some of the fission products of both 235U and 239Pu , and therefore used as indicators of nuclear explosions . 
 Naturally occurring xenon is made of eight stable isotopes , the most of any element with the exception of tin , which <a href='got' title='1'><mark>has</mark></a> ten . Xenon and tin <a href='drop_aux' title='2'><mark>are</mark></a>the only elements to have more than seven stable isotopes . The isotopes 124Xe and 134Xe are predicted to undergo double beta decay , but this <a href='been_done' title='3'><mark>has</mark></a> never been observed so they are considered to be stable . Besides these stable forms , <a href='dey_it' title='4'><mark>there</mark></a> are over 40 unstable isotopes <a href='null_relcl' title='5'><mark>that</mark></a><a href='been_done' title='6'><mark>have</mark></a> been studied . The longest lived of these isotopes <a href='drop_aux' title='7'><mark>is</mark></a>136Xe , which <a href='been_done' title='8'><mark>has</mark></a> been observed to undergo double beta decay with a half @-@ life of 2 @.@ 11 × 1021 yr . 129Xe is produced by beta decay of 129I , which <a href='got' title='9'><mark>has</mark></a> a half @-@ life of 16 million years , while 131mXe , 133Xe , 133mXe , and 135Xe <a href='drop_aux' title='10'><mark>are</mark></a>some of the fission products of both 235U and 239Pu , and therefore used as indicators of nuclear explosions . 
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