Probing the Nuclear Structure of ²⁹Si with the (α,dγ) Reaction

(α, d) reactions strongly populate fully-aligned states. To find the fully aligned state in ²⁹Si, an (α,d) singles experiment was previously performed at the FSU Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Laboratory [1]. A candidate was observed at 13.73 MeV. A subsequent ²⁷Al(α,dγ)²⁹Si experiment was conducted with the SE-SPS and the CeBrA Demonstrator [2] to investigate the gamma decay of excited states in ²⁹Si up to that excitation energy. Aided by the coincident γ-ray detection, we observed a stark change in γ-decay behavior at around 11 MeV in excitation energy, where the candidate for the fully-aligned state is located. Excited states below 11 MeV predominantly decay through the first 5/2⁺ state, while excited states above 11 MeV predominantly decay through the second 5/2⁺ state. Nuclear structure changes between the two 5/2⁺ states or for the groups of higher-lying states might explain the experimental observation. Details of the experiment will be presented, and the possible origin of the structure change will be discussed.