New Method for Distorted-Wave Analysis of Stripping to Unbound States

Emergence of theN=16shell gap inO21

“…The 4.77 MeV state is identified as 3/2 + and carries some 60% of the ν0d 3/2 strength. The spectroscopic factor agrees with the USDA interaction calculations that correctly predict 26 O to be unbound. The N=16 shell gap was thus estimated to be 5.1(11) MeV, somewhat larger than the lower limit of 3.55(10) MeV derived from the energy difference between the 3/2 + resonance and the 1/2 + level.…”

“…Two neutron unbound states were observed at excitation energies of 4.77 (10) and 6.17(11) MeV. The spectroscopic factor deduced for the lower of these, interpreted as a 3/2 + level, reveals a relatively pure (60%) 0d 3/2 single-particle configuration, in good agreement with shell-model calculations which predict 26 O to be unbound. The large energy difference between the 3/2 + and 1/2 + states is indicative of the emergence of the N=16 shell gap, which is estimated to be 5.1(11) MeV.…”

“…The simulation was then used to estimate the resolution at higher excitation energies. The adjustment to the data yielded energies and widths for the resonances of E res1 = 0.96(10), Γ 1 =0.46 (20) and E res2 =2.36(11), Γ 2 =0.32 (26) MeV. The corresponding excitation energies are 4.77(10) and 6.17(11) MeV.…”

“…The Chapel-Hill parameterisation (CH89) [25] was used to describe the nucleon-nucleus potentials for both the entrance and outgoing channels. The calculations for the unbound states were performed using the Vincent and Fortune prescription [26] implemented in DWUCK4 [27]. The neutron single-particle form factors were obtained using a Woods-Saxon potential with the depth adjusted to reproduce the experimental binding energy of each level.…”

Investigation of the unbound21C nucleus via transfer reaction

“…(1), in the zero range limit when the residual nucleus is unbound. This is due to the oscillating behavior of the n-20 C wave functions in the asymptotic region, and some treatments were suggested [10][11][12] to resolve this problem. In the present study, we took 80 fm for the space of the n-20 C wave function in the pseudo states approach, which could be quite far away from the convergence.…”