( ( ( ( 1-1976 -RRB- ) ( Radioisotope ( A radioactive ) ) ) isotope ) . )
(ROOT (SQ (VP (VB 1-1976) (-RRB- -RRB-) (NP (NNP Radioisotope) (DT A) (NN radioactive)) (ADVP (RB isotope))) (. .)))
1-1976) Radioisotope A radioactive isotope.
(ROOT (S (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NNS radioisotopes)) (VP (VBZ is) (NP (NP (DT an) (NN isotope)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (JJ radioactive))))))) (. .)))