( ( ( This rate ) ( of decay ) ) ( ( is ( measured ( by ( half-life ( -LRB- ( ( ( how long ) ( it ( ( takes ( for ( one-half ( of ( the ( parent ( radioactive material ) ) ) ) ) ) ) ( to ( decay ( to ( a ( daughter product ) ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT This) (NN rate)) (PP (IN of) (NP (NN decay)))) (VP (VBZ is) (VP (VBN measured) (PP (IN by) (NP (NP (NN half-life)) (PRN (-LRB- -LRB-) (SBAR (WHADVP (WRB how) (RB long)) (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (NN one-half)) (PP (IN of) (NP (DT the) (NN parent) (NN radioactive) (NN material))))) (PP (TO to) (NP (NP (NN decay)) (PP (TO to) (NP (DT a) (NN daughter) (NN product)))))))) (-RRB- -RRB-)))))) (. .)))
This rate of decay is measured by half-life (how long it takes for one-half of the parent radioactive material to decay to a daughter product).
(ROOT (S (NP (DT The) (NN decay) (NN rate)) (VP (VBZ is) (VP (VBN measured) (PP (IN in) (NP (NP (DT a) (NN unit)) (VP (VBN called) (NP (DT the) (NN half-life))))))) (. .)))