( This ( ( is ( called ( a ( carbon ( 14 isotope ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (VP (VBN called) (NP (DT a) (NN carbon) (CD 14) (NN isotope)))) (. .)))
This is called a carbon 14 isotope.
(ROOT (S (NP (NP (NNP Carbon) (CD 14) (NN isotope)) (PP (IN of) (NP (NN carbon)))) (VP (VBZ is) (ADVP (RB typically)) (VP (VBN used) (PP (TO to) (NP (NN date) (JJ ancient) (NNS items))))) (. .)))