( ( ( The half-life ) ( -LRB- ( ( ( t & ) ( frac12 ; ) ) -RRB- ) ) ) ( ( is ( ( the time ) ( it ( ( takes ( for ( half ( the isotope ) ) ) ) ( to decay ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN half-life)) (PRN (-LRB- -LRB-) (NP (NP (CD t) (CC &)) (SBAR (S (VP (VBZ frac12)) (: ;)))) (-RRB- -RRB-))) (VP (VBZ is) (NP (NP (DT the) (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (PDT half) (DT the) (NN isotope))) (PP (TO to) (NP (NN decay)))))))) (. .)))
The half-life (t &frac12; ) is the time it takes for half the 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)))))))))) (. .)))