( ( ( The period ) ( of ( time ( it ( ( takes ( for ( one-half ( of ( the ( radioactive material ) ) ) ) ) ) ( to decay ) ) ) ) ) ) ( ( is ( called ( ( the half-life ) ( of ( the isotope ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN period)) (PP (IN of) (NP (NP (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (NN one-half)) (PP (IN of) (NP (DT the) (JJ radioactive) (NN material))))) (PP (TO to) (NP (NN decay))))))))) (VP (VBZ is) (VP (VBN called) (NP (NP (DT the) (NN half-life)) (PP (IN of) (NP (DT the) (NN isotope)))))) (. .)))
The period of time it takes for one-half of the radioactive material to decay is called the half-life of the isotope.
(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)))))))))) (. .)))