 − 3 × <unk> years , giving about 1 alpha decay per two minutes in every kilogram of natural europium . This value is in reasonable agreement with theoretical predictions . Besides the natural <unk> 151Eu , 35 artificial <unk> have been characterized , the most stable being <unk> with a half @-@ life of 36 @.@ 9 years , 152Eu with a half @-@ life of 13 @.@ 516 years , and 154Eu with a half @-@ life of 8 @.@ 593 years . All the remaining radioactive isotopes have half @-@ lives shorter than 4 @.@ <unk> years , and the majority of these have half @-@ lives shorter than 12 @.@ 2 seconds . This element also has 8 meta states , with the most stable being <unk> ( t1 / 2 = 12 @.@ 8 hours ) , <unk> ( t1 / 2 = 9 @.@ <unk> hours ) and <unk> ( t1 / 2 = 96 minutes ) . 
