( ( ( half-life ( The amount ) ) ( of time ) ) ( ( ( needed ( for ( half ( of ( ( the atoms ) ( of ( a ( radioactive material ) ) ) ) ) ) ) ) ( to decay ) ) . ) )
(ROOT (S (NP (NP (NN half-life) (DT The) (NN amount)) (PP (IN of) (NP (NN time)))) (VP (VBD needed) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN of) (NP (DT a) (JJ radioactive) (NN material))))))) (PP (TO to) (NP (NN decay)))) (. .)))
half-life The amount of time needed for half of the atoms of a radioactive material 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)))))))))) (. .)))