| dc.description.abstract | Ground state stable nuclei typically have spherical geometries but may exhibit exotic shapes and form α-particle clusters within their bulk if given excitation energy and/or angular momentum. It is predicted that such clustering can promote the production of angular-momentum stabilized toroidal nuclei. Previously, an experiment was performed using the NIMROD detector array where high-excitation energy peaks were observed in the 7-α particle disassembly of ^28Si in collisions of ^28Si + ^12C at 35 MeV/nucleon; these peaks were attributed to the breakup of toroidal high-spin isomer states. However, the angular resolution of NIMROD is determined by the size of the individual silicon detectors, giving large uncertainties when reconstructing the excitation energy of the fragmenting source. This motivated the present work, where these collisions were measured with improved angular resolution using the Forward Array Using Silicon Technology (FAUST). FAUST is equipped with resistive dual-axis duo-lateral (DADL) position-sensitive silicon detectors capable of sub-millimeter position resolution. Due to the detector charge-splitting mechanism, position dependence of the measured energy as well as distortions in calculated particle positions were observed when using conventional signal processing electronics. A charge determination method has been developed that greatly minimizes these distortions. The performance and response of the array was characterized in detail to accurately predict the expected resolution of measuring narrow resonances. The measured excitation energy distributions for 7- and 8-α disassembly events showed no strong evidence for highly excited states, in contradiction with the NIMROD experiment. Further investigation of collision properties that lead to these exit channels revealed challenges in isolating clean projectile-mass decays, where many 7-α events do not originate from a single ^A28Si source. A statistical likelihood analysis was performed to determine the sensitivity of the present measurement for confidently determining resonant yield, providing an upper limit to toroidal high-spin isomer cross section as a function of the excitation energy and width of potential states. | |
