GEANT4 Simulations of Electron Capture Branching Ratio Measurements for the TITAN Facility

A novel technique has been developed to measure the electron capture branching ratios (ECBRs) of key intermediate nuclei involved in double-b decay using the TITAN facility, TRIUMF’s Ion Trap for Atomic and Nuclear Science Facility. Knowledge of ECBRs is essential to evaluate the nuclear matrix elements of double-b decay for both two-neutrino double-b decay (2nbb) and neutrino-less double-b decay (0nbb) processes. In most of the cases of interest the ECBRs are poorly known or completely unknown because the EC process is suppressed by several orders of magnitude relative to their b-decay counterpart due to energy consideration. In addition, traditional methods of measuring these ratios suffer from large backgrounds due to the many orders of magnitude more intense b-decay. A new method for measuring EC branching ratios was implemented by using the TITAN ion trap at the TRIUMF ISAC (Isotope Separator and Accelerator) radioactive beam facility. In these experiments the Electron Beam Ion Trap (EBIT) is used as a spectroscopy Penning trap, where the electrons from b-decay will be confined by trap’s magnetic field and transported out of the trap, while the x-rays from EC are detected by Si(Li) x-ray detectors that are radially installed around the trap through seven open ports towards the trap’s center. A comprehensive GEANT4 based Monte-Carlo simulation has been developed to optimize the TITAN-EC experimental set-up and measurements at TRIUMF as analytical tool. The developments, evolution and validation of this Monte-Carlo simulation tool are described in this thesis.