The decay of the 21.47-MeV stretched resonance in ¹³C: A precise probe of the open nuclear quantum system description

The decay of the 21.47-MeV stretched resonance in ¹³C, arising from p_3/2→d_5/2 nucleon excitation coupled to maximum spin, was investigated in a (p,p^′) experiment at 135 MeV proton bombarding energy, performed at the Cyclotron Centre Bronowice (CCB) at IFJ PAN in Krakow. First experimental information on the proton and neutron decay branches from this state was obtained by using coincidence measurement of protons inelastically scattered on a ¹³C target and γ rays from daughter nuclei, namely, ¹²B (proton decay) and ¹²C (neutron decay). The main branches lead to the J^π=2⁺, first-excited state at 0.953 MeV in ¹²B, and to the J^π=1⁺, T=1 level at 15.110 MeV in ¹²C. The results were compared with predictions from the Gamow Shell Model (GSM), which was used to describe the stretched resonance in terms of its energy, width, electromagnetic transition strengths and decay pattern. A very good agreement was obtained between the measured and calculated properties of the 21.47-MeV stretched resonance in ¹³C, demonstrating the high-quality and precision of the GSM wave function calculations, which include coupling to the resonant and non-resonant particle continuum.