argon-39 atom CAS:25729-41-3 Ar-39 radioisotope PMID:30487580 PMID:16429279 A trace radioisotope of argon with atomic mass of 38.964313 and a half-life of 269 years. PMID:28017500 argon-39 PMID:28755564 CHEBI:155827 38.96431 [39Ar] argon 39 InChI=1S/Ar/i1-1 Ar-39 38.964 (39)Ar 0 PMID:17791262 [Ar] XKRFYHLGVUSROY-BJUDXGSMSA-N argon, isotope of mass 39 chebi_ontology (39)18Ar PMID:17781454 (39)Ar radioisotope argon atom