Cross-shell Phenomena in Mass 36 Al and Si Isotopes Investigated via β-Decays

The β-decays of ³⁶Mg and ³⁶Al were studied at the National Superconducting Cyclotron Laboratory (NSCL) to extract the half-lives of the parent nuclei and reveal the nuclear structure of the decaying descendants. Neutron-rich ³⁶Mg and ³⁶Al were produced at the NSCL's Coupled Cyclotron Facility via projectile fragmentation of a ⁴⁸Ca beam of energy 140 MeV/u impinged on a 642 mg/cm² thick ⁹Be target. The fragmented beam was delivered to the decay station after being resolved by the A1900 separator. Two Si p-i-n detectors were used for the particle identification whereas the ions were implanted on a 3-mm thick CeBr₃ scintilator. The β-delayed γ-rays were identified with 16 Ge (SeGA) and 15 LaBr₃ detectors. The half-lives of the two parent nuclei were determined. β-delayed γ-ray transitions were observed in ³⁶Al and ³⁶Si for the first time. Excited energy states of ³⁶Al populated by the β-decay of ³⁶Mg are proposed, whereas only the ground state information was available prior to this work. The experimental results were interpreted by using the nuclear configuration interaction studies with the FSU shell-model Hamiltonian. The results will shed light on our understanding of the structure of more exotic neutron-rich nuclei to be produced with the next generation facilities like FRIB.