( ( Some ( of ( these isotopes ) ) ) ( ( ( ( ( have ( half-lives ( of ( ( tens ( of thousands ) ) ( of years ) ) ) ) ) , ) and ) ( therefore ( require ( long-term isolation ) ) ) ) . ) )
(ROOT (S (NP (NP (DT Some)) (PP (IN of) (NP (DT these) (NNS isotopes)))) (VP (VP (VBP have) (NP (NP (NNS half-lives)) (PP (IN of) (NP (NP (QP (NNS tens) (IN of) (NNS thousands))) (PP (IN of) (NP (NNS years))))))) (, ,) (CC and) (VP (ADVP (RB therefore)) (VBP require) (NP (JJ long-term) (NN isolation)))) (. .)))
Some of these isotopes have half-lives of tens of thousands of years, and therefore require long-term isolation.
(ROOT (S (NP (DT The) (JJ long-lived) (NNS isotopes)) (VP (VBP require) (NP (NP (NNS thousands)) (PP (IN of) (NP (NP (NNS years)) (PP (TO to) (NP (NN decay)))))) (PP (TO to) (NP (NP (DT a) (JJ safe) (NN level)) (PP (IN in) (NP (DT a) (JJ nuclear) (NN reactor)))))) (. .)))