TACTIC: the TRIUMF Annular Chamber for Tracking and Identification of Charged Particles

An in-depth characterization of the TACTIC detector was performed using data from a Gd-148 alpha source and some test runs with a stable ion beam. The detector is an active target time-projection chamber with a blind central region for maximizing beam tolerance and GEM-based electron amplification, equipped with a modern digitizing data acquisition system allowing the recording of full signals. The system was developed to study the reaction Li-8(alpha,n)B-11, which is important for bridging the mass 8 gap in scenarios of low He-4 density like Inhomogeneous Big Bang Nucleosynthesis and the production of r-process seeds in supernovae. Both energy resolution and tracking accuracy were found to agree with theoretical predictions and Geant4 simulations. The Li-8 beam rate capability of the system is predicted to be of the order of 10(5)s(-1), several orders of magnitude higher than most previous measurements of the same reaction, while still maintaining a high detection efficiency of 70 % to 80 %.