( ( ( The amount ) ( of ( time ( it ( ( takes ( for ( half ( of ( ( a sample ) ( of ( ( radioactive material ) ( to decay ) ) ) ) ) ) ) ) ( into ( ( a ( stable substance ) ) ( in ( this way ) ) ) ) ) ) ) ) ) ( ( is ( called ( the 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 (NP (DT a) (JJ stable) (NN substance)) (PP (IN in) (NP (DT this) (NN way))))))))))) (VP (VBZ is) (VP (VBN called) (NP (DT the) (NN half-life)))) (. .)))
The amount of time it takes for half of a sample of radioactive material to decay into a stable substance in this way is called the 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)))))))))) (. .)))