Geochronology by the 40Ar/39Ar method at the Sernageomin Laboratory, Santiago, Chile

40K undergoes a branched decay to 40Ca (89.5%) and 40Ar (10.5%). The 40K to 40Ar decay has a half-life of 1.25 x 109 years, and is thus suitable for the study of the age of potassium-bearing geological materials which have the capacity to retain radiogenic argon. At the Servicio Nacional de Geologia y Mineria, a potassium-argon laboratory has been operating since 1980. Over this 20-year period, about 7000 K-Ar analyses have been performed in this laboratory. In 1998 a 40Ar/39Ar laboratory was constructed, the first of its kind in South America (there is now a second laboratory in Brazil). This presentation deals with the applications of 40Ar/39Ar geochronology in Chile, limitations and development of irradiation methodology, and the role of the CCHEN reactor for the SERNAGEOMIN laboratory. Since the inauguration of the SERNAGEOMIN 40Ar/39Ar Geochronology Laboratory, the close working relationship with the CCHEN has proved vital in the development of a suitable irradiation methodology, the standardization of sample processing throughout the entire analytical chain and the implementation of safety norms for the manipulation of radioactive samples. Future development and improvement of the method, such as the implementation of sample rotation during irradiation and possible changes in sample holder design, are dependent upon this relationship