Automatic activation analysis at a TRIGA reactor

Automatic Activation Analysis (AAA) is rendered possible by a unique neutron activation analysis facility for short-lived isomeric transitions based on a fast rabbit system with sample changer and sample separation, and an adaptive digital gamma spectrometer for very high counting rates of up to 106 c/s. The system is governed by a computer program performing irradiation control, neutron flux monitoring, and gamma spectrometry with realtime correction of counting losses, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic flow of operations. As spectrometry is done by means of hundreds of sequentially measured pairs of concurrently recorded loss-corrected and non corrected spectra, concentrations are derived from an optimally weighted average of all individual occurrences in this sequence of spectra which also enables the separation of isomeric transitions with coinciding energies but different half-lives such as 116m2In (162.4 keV, t1/2 = 2.2 s) and 77mSe (162.2 keV, t1/2 17.4 s). An expert system for AAA specifically designed for Triga reactors and thus avoiding the procedural obstacles of ordinary activation analysis could be extremely helpful to facilitate the introduction of neutron activation analysis (NAA) at research reactors in developing countries where appropriate specialists are not (yet) available. (author)