( It ( ( ( decays ( by ( beta decay ) ) ) ( with ( ( a half-life ) ( of ( 14.29 days ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ decays) (PP (IN by) (NP (JJ beta) (NN decay))) (PP (IN with) (NP (NP (DT a) (NN half-life)) (PP (IN of) (NP (CD 14.29) (NNS days)))))) (. .)))
It decays by beta decay with a half-life of 14.29 days.
(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))))))) (. .)))