Fission: Impossible? Search for fission of 230Ac

Licentiatavhandling, 2025

A novel and versatile approach for studying (d,pF) reactions using the ISOLDE Solenoidal Spectrometer (ISS) at CERN is presented. Specifically designed
to maximize the detection efficiency for fission fragments in coincidence with a proton from a (d,pF) reaction within the 2 T magnetic field of the ISS, this setup will enable the precise extraction of fission probabilities of neutron-rich nuclei as a function of excitation energy. Furthermore, dedicated γ-ray measurements will provide additional insights into the total energy and multiplicity of γ-rays emitted during the fission process. Extensive simulations are conducted to optimize the experimental setup, leading to significant improvements in the detection efficiency of fission fragments. A CD-shaped silicon detector is chosen to enhance the detection of the fragments that are strongly forward-peaked in the laboratory frame due to the kinematic boost in inverse kinematics. This design achieves a detection efficiency eight times higher than that of gas-filled fission fragment detectors used in a previous proof-of-principle experiment. Additionally, the case is made for an innovative off-axis configuration for the beam luminosity monitor, contrary to the standard on-beam approach. This choice minimizes interference with fission fragment trajectories and, through the additional position information provided by the detector, significantly improves the signal-to-background ratio. The compact and modular design of this experimental setup also facilitates the detection of γ-rays emitted from fission fragments, offering a comprehensive characterization of the fission process. These developments are driven by the upcoming experiment to investigate the fission of 230Ac using a radioactive 229Ac beam, marking the first such measurement for this isotope. Importantly, the versatility of this approach makes it adaptable for studying other isotopes of interest in future experiments.