( ( Define ( halflife ( as ( ( the amount ) ( of ( time ( ( required ( for ( half ( of ( the ( parent isotopes ) ) ) ) ) ) ( to decay ) ) ) ) ) ) ) ) . )
(ROOT (S (VP (VB Define) (ADJP (JJ halflife) (PP (IN as) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN time)) (VP (VBN required) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (DT the) (NN parent) (NNS isotopes))))) (PP (TO to) (NP (NN decay)))))))))) (. .)))
Define halflife as the amount of time required for half of the parent isotopes to decay.
(ROOT (S (NP (DT The) (NN term) (NN half-life)) (VP (VBZ decribes) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN time)) (VP (VBN required) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (DT the) (JJ original) (NN material))))) (PP (TO to) (NP (NP (NN decay)) (PP (IN in) (NP (DT an) (NN isotope)))))))))) (. .)))