( ( ( ( ( Strontium 90 ) , ) ( with ( ( a half-life ) ( of ( twenty-eight years ) ) ) ) ) , ) ( ( is ( a ( long-lived isotope ) ) ) . ) )
(ROOT (S (NP (NP (NNP Strontium) (CD 90)) (, ,) (PP (IN with) (NP (NP (DT a) (NN half-life)) (PP (IN of) (NP (JJ twenty-eight) (NNS years))))) (, ,)) (VP (VBZ is) (NP (DT a) (JJ long-lived) (NN isotope))) (. .)))
Strontium 90, with a half-life of twenty-eight years, is a long-lived isotope.
(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)))))) (. .)))