Development of TACTIC: a novel detector for nuclear astrophysics

Active-target detectors play a significant role in low-energy nuclear physics. The ability to utilise low intensity radioactive beams and a flexible choice of target gas enable these detectors to make direct measurements of a variety of nuclear reactions. This thesis focuses on the development and commissioning of TACTIC, a cylindrical active-target TPC. The design of TACTIC is suitable for the cross section measurement of alpha-induced charged particle reactions at low centre of mass energies. The measurements rely on the identification of charged particles by means of differential energy loss in the detection medium. In order to detect the reaction products over a wide range of energies, the novel μ-RWELL (micro-Resistive WELL) detectors are used as the gas multiplication stage. A unique concentric cathode cage configuration is also used to trap the ionisation electrons from the unreacted beam ions, which enables TACTIC to accommodate higher beam intensities (> 10^6 pps), compared to other active target detectors. Furthermore, an adjustable extended gas target allows simultaneous cross section measurements at multiple centre of mass energies. A detailed characterisation of the detector and the first successful cross section measurement at the TRIUMF ISAC-I facility are documented in this work. The astrophysically important 23Na(α, p)26Mg reaction was studied in inverse kinematics as a commissioning experiment.

This thesis also includes the study of the μ-RWELL detectors with the test chamber, which is a planar analogue of TACTIC. A series of alpha and 55Fe X-ray source tests were used to study the performance and optimum operating conditions of the μ-RWELL detectors in terms of gas gain and energy resolution achievable as well as the low-energy detection capability (∼ few keV) in different gas mixtures of interest. The installation marked the very first integration of the state-of-the-art μ-RWELL technology inside a cylindrical geometry for charged particle tracking.