New determination of proton spectroscopic factors and reduced widths for ~8Be states in the 16.5–18.0 MeV excitation energy region via the study of the ~7Li (~3He,d)~8Be transfer reaction at E_(lab) = 20 MeV: Implication for the ~7Li( p, α) ~4He hydrogen burning reaction

摘要

The angular distributions of 8Be states in the excitation energy region E_x ～ (16.5–18.2) MeV produced in the ~7Li(~3He,d)~8Be proton transfer reaction have been measured at the Orsay 14.8−MV tandem accelerator for ~3He~(2+) ion bombarding energy, E_(lab) = 20 MeV, and forward angular range, θ_ (lab) = 5°–50°. A high energy resolution detection system composed of a split-pole magnetic spectrometer and a △E − E, position-sensitive drift chamber was used to record the energy spectra of outgoing deuterons. The measured cross section data for the direct reaction component have been separated from the compound nucleus one, then analyzed in the framework of the nonlocal, finite-range (FR)–distorted-wave Born approximation (DWBA) theory. New values of the C~2S and (S_(p1/2), S_(p3/2)) proton absolute and partial spectroscopic factors and related γ _p~2 (a) proton reduced widths versus the p + ~7Li channel radius have been extracted for the 2~+(16.626) and 2+(16.922),T = 0 + 1 isospin-mixed loosely bound states of astrophysical interest and the 1~+(17.640), T = 1 unbound state of ~8Be. They are compared to sparse earlier experimental values and to shell-model-predicted ones from the literature, and are discussed. In particular, the status of the spectroscopic information on the 2~+ isospin-mixed doublet is reviewed and updated. The application in nuclear astrophysics of the DWBA derived results is emphasized.