( ( ( The amount ) ( of ( time ( it ( ( takes ( for ( half ( of ( ( a sample ) ( of ( ( radioactive material ) ( to decay ) ) ) ) ) ) ) ) ( into ( a ( stable substance ) ) ) ) ) ) ) ) ( ( is ( called ( its half-life ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN amount)) (PP (IN of) (NP (NP (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (NP (DT a) (NN sample)) (PP (IN of) (NP (NP (JJ radioactive) (NN material)) (PP (TO to) (NP (NN decay))))))))) (PP (IN into) (NP (DT a) (JJ stable) (NN substance))))))))) (VP (VBZ is) (VP (VBN called) (NP (PRP$ its) (NN half-life)))) (. .)))
The amount of time it takes for half of a sample of radioactive material to decay into a stable substance is called its half-life .
(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)))))))))) (. .)))