C-14/C-12 isotopic ratio of a research nuclear reactor graphite control bar

In this work we determine the C-14 content in a graphite bar used in the core of the research nuclear reactor TRIGA MARK III, at the "Instituto Nacional de Investigaciones Nucleares" (ININ) in Mexico. The C-14/C-12 ratio was measured, using Accelerator Mass Spectrometry (AMS) at the Laboratorio Nacional de Espectrometria de Masas con Aceleradores (LEMA) at the "Instituto de Fisica de la Universidad Nacional Autonoma de Mexico" (IFUNAM). Our results show a C-14 ratio over three orders of magnitude higher than that found in modern organic matter. A gamma-ray spectroscopy study of the graphite bar with a High Purity Germanium detector (HPGe) shows the presence of the same radioactive isotopes reported in previous studies of similar bars.