( ( ( The ( radioactivity level ) ) ( of ( ( an isotope ) ( such ( as plutonium ) ) ) ) ) ( ( is ( determined ( by ( ( ( its half-life ) , ) ( which ( is ( ( the time ) ( it ( ( takes ( for ( half ( of ( an ( original quantity ) ) ) ) ) ) ( to decay ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN radioactivity) (NN level)) (PP (IN of) (NP (NP (DT an) (NN isotope)) (PP (JJ such) (IN as) (NP (NN plutonium)))))) (VP (VBZ is) (VP (VBN determined) (PP (IN by) (NP (NP (PRP$ its) (NN half-life)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (NP (NP (DT the) (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (DT an) (JJ original) (NN quantity))))) (PP (TO to) (NP (NN decay)))))))))))))) (. .)))
The radioactivity level of an isotope such as plutonium is determined by its half-life, which is the time it takes for half of an original quantity 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)))))))))) (. .)))