9 . ▁ ▁No ble ▁g ases ▁( x en on , ▁k rypt on ) ▁are ▁vol atile ▁even ▁without ▁flu or id ation , ▁and ▁will ▁not ▁con den se ▁except ▁at ▁much ▁lower ▁temper atures . ▁ ▁Left ▁behind ▁are ▁alk ali ▁met als ▁( ca es ium , ▁rub id ium ), ▁al kal ine ▁earth ▁met als ▁( str ont ium , ▁b arium ), ▁l anth an ides , ▁the ▁remaining ▁act in ides ▁( amer ici um , ▁cur ium ), ▁remaining ▁transition ▁met als ▁( y tt rium , ▁z ir con ium , ▁p all ad ium , ▁silver ) ▁and ▁post - transition ▁met als ▁( t in , ▁ind ium , ▁cad m ium ). ▁This ▁fraction ▁contains ▁the ▁f ission ▁products ▁that ▁are ▁radiation ▁ha z ards ▁on ▁a ▁scale ▁of ▁dec ades ▁( C s - 1 3 7 , ▁Sr - 9 0 , ▁Sm - 1 5 1 ), ▁the ▁four ▁remaining ▁long - l ived ▁f ission ▁products ▁Cs - 1 3 5 , ▁Z r - 9 3 , ▁P d - 1 0 7 , ▁Sn - 1 2 6 ▁of ▁which ▁only ▁the ▁last ▁em its ▁strong ▁radiation , ▁most ▁of ▁the ▁neut ron ▁po isons , ▁and ▁the ▁higher ▁act in ides ▁( amer ici um , ▁cur ium , ▁cal if or ni um ) ▁that ▁are ▁radiation ▁ha z ards ▁on ▁a ▁scale ▁of ▁hundreds ▁or ▁thousands ▁of ▁years ▁and ▁are