One-step energy scanning of wide low-lying 1− resonances in 13C+p and 13N+p scattering

Thick polyethylene targets have been bombarded with 8.2 MeV 13C and 13N beams accelerated by a cyclotron, i.e. having a relatively large energy spread of about 200 keV. Recoil protons have been detected in order to observe the Jπ=1− wide resonances at E∗=8.06 and 5.17 MeV in the 14N and 14O compound nuclei, respectively. It is shown that accurate values of the energy, width and spin of the resonant states can be obtained under experimental conditions which, at first glance, may seem inappropriate. The method is well suited for resonance studies using radioactive beams. The measured width of the 14N resonance (Λ=33.7±1.0 keV) disagrees with a recent measurement (Λ=23 keV). The energy of the 14O resonance was determined to be Ec.m.=526±3 keV instead of 545±10 keV as quoted in the literature. A new paramater-free microscopic calculation was undertaken to solve an apparent discrepancy between the experimental proton width and a previous calculation.