( ( The half-life ) ( ( is ( defined ( as ( ( the time ) ( ( required ( for ( half ( of ( ( the atoms ) ( of ( a ( particular isotope ) ) ) ) ) ) ) ) ( to decay ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN half-life)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT the) (NN time)) (VP (VBN required) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN of) (NP (DT a) (JJ particular) (NN isotope))))))) (PP (TO to) (NP (NN decay)))))))) (. .)))
The half-life is defined as the time required for half of the atoms of a particular isotope 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)))))))))) (. .)))