The8Li(p,α)5He reaction at low energies, and

D. R. Mendes

¹

,

A. Lépine‐Szily

²

,

Pierre Descouvemont

³

et al.

Abstract

We present a direct measurement of the low-energy 8 Li(p, α) 5 He cross section, using a radioactive 8 Li beam impinging on a thick target. With four beam energies, we cover the energy range between E c.m. = 0.2 and 2.1 MeV. An R-matrix analysis of the data is performed and suggests the existence of two broad overlapping resonances (5/2+ at E c.m. = 1.69 MeV and 7/2 + at E c.m. = 1.76 MeV). At low energies our data are sensitive to the properties of a subthreshold state (E x = 16.67 MeV) and of two resonances above threshold. These resonances were observed in previous experiments. The R-matrix fit confirms spin assignments, and provides partial widths. We propose a new 8 Li(p, α) 5 He reaction rate and briefly discuss its influence in nuclear astrophysics.

Spectroscopy of high lying resonances in9Be produced with radioactive8Li beams

“…In the first experiment [1], only the first solenoid was used. When using only one solenoid, the secondary beam still has some contaminants easily identified in elastic scattering experiments.…”

“…The contribution of these α-particles, as well as the continuous energy distributions of α-particles resulting from the 3-body break-up, were calculated and subtracted from the energy spectra. All details of these calculations can be obtained in the reference of Mendes et al [1]. We performed measurements at four different incident energies, the 8 Li secondary beam energies incident on the thick [CH 2 ] n secondary target were, respectively 13.2, 14.5, 17.0 and 19.0 MeV.…”

“…In this work, we present our recently published results [1] of the 8 Li(p,α) 5 He reaction, together with preliminary results of the 8 Li(p,p) 8 Li cross sections at low energies. These experiments have been performed at RIBRAS (Radioactive Ion Beams in Brazil) [5,6] with a 8 Li radioactive beam (τ 1/2 ≈ 0.8 s).…”

“…The 9 Be level scheme is well known at low excitation energies [7,8], but the high-energy region is still uncertain. The 8 Li(p,α) 5 He reaction [1] allows the precise determination of several resonance parameters: energies, spins, proton and alpha widths. A transfer reaction offers several advantages.…”

RIBRAS: The Facility for Exotic Nuclei in Brazil

“…The presence of peaks in the spectra is related to resonances in the compound system. This technique allows spectrocopic studies of light nuclei like 7 Li and 9 Be at relatively high excitation energies [14,15]. Contaminant reactions in the Carbon of the CH 2 target can be subtracted by measurements using a pure Carbon target and the presence of contaminations in the secondary beam can be monitored using a pure Gold target, where just scattering (no reactions) takes place.…”