 152Eu ( half @-@ life 13 @.@ 516 years ) and 154Eu ( half @-@ life 8 @.@ 593 years ) cannot be beta decay products because <unk> and <unk> are non @-@ radioactive , but 154Eu is the only long @-@ lived " shielded " <unk> , other than <unk> , to have a fission yield of more than 2 @.@ 5 parts per million <unk> . A larger amount of 154Eu is produced by neutron activation of a significant portion of the non @-@ radioactive 153Eu ; however , much of this is further converted to <unk> . 
