( ( ( half-life ( ( The amount ) ( of time ) ) ) ( that ( it ( ( takes ( for ( ( one half ) ( of ( ( an ( original population ) ) ( of ( atoms ( of ( a ( radioactive isotope ) ) ) ) ) ) ) ) ) ) ( to decay ) ) ) ) ) . )
(ROOT (S (VP (VB half-life) (NP (NP (DT The) (NN amount)) (PP (IN of) (NP (NN time)))) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (CD one) (NN half)) (PP (IN of) (NP (NP (DT an) (JJ original) (NN population)) (PP (IN of) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT a) (JJ radioactive) (NN isotope))))))))) (PP (TO to) (NP (NN decay))))))) (. .)))
half-life The amount of time that it takes for one half of an original population of atoms of a radioactive 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)))))))))) (. .)))