( ( H H ) ( ( ( ( half-life ( The time ) ) ( for ( ( the activity ) ( of ( ( a ( radioactive isotope ) ) ( to decay ) ) ) ) ) ) ( to ( half ( its ( original value ) ) ) ) ) . ) )
(ROOT (S (NP (NNP H) (NNP H)) (VP (VBD half-life) (NP (DT The) (NN time)) (PP (IN for) (NP (NP (DT the) (NN activity)) (PP (IN of) (NP (NP (DT a) (JJ radioactive) (NN isotope)) (PP (TO to) (NP (NN decay))))))) (PP (TO to) (NP (PDT half) (PRP$ its) (JJ original) (NN value)))) (. .)))
H H half-life The time for the activity of a radioactive isotope to decay to half its original value.
(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)))))))))) (. .)))