Resonance parameters of the first1/2+state inBe9and astrophysica

Abstract

Spectra of the 9 Be(e,e) reaction have been measured at the Superconducting Darmstadt Electron Linear Accelerator at an electron energy of E 0 = 73 MeV and scattering angles of 93 • and 141 • with high-energy resolution up to excitation energies of E x = 8 MeV. The astrophysically relevant resonance parameters of the first excited 1/2 + state of 9 Be have been extracted in a one-level approximation of R-matrix theory, resulting in resonance energy E R = 1.748(6) MeV and width R = 274(8) keV, which are in good agreement with the latest 9 Be(γ ,n) experiment but with considerably improved uncertainties. However, the reduced B(E1) transition strength deduced from an extrapolation of the (e,e) data to the photon point is smaller by a factor of two. Implications of the new results for possible production of 12 C in neutron-rich astrophysical scenarios are discussed.

Astrophysical reaction rate forBe9formation within a three-body approach

“…It shows a Borromean structure, since none of the binary subsystems 5 He nor 8 Be are bound. 9 Be is a loosely bound system with a 3/2 − ground state located at 1.5736 MeV below the α + α + n threshold [36].…”

“…The presence of a very narrow two-body 8 Be resonance at 0.092 MeV above the three-body threshold suggests a sequential description of the formation process [3]. Due to the small lifetime of the 5 He system (∼ 10 −21 s) compared to 8 Be (∼ 10 −16 s), the sequential synthesis is considered to proceed mainly through 8 Be [37]. Nevertheless, the sequential picture may underestimate the reaction rate at low temperature by several orders of magnitude [14].…”

“…However, in neutron rich environments, the reaction α(αn, γ) 9 Be followed by 9 Be(α, n) 12 C may dominate over, depending on the astrophysical conditions [3]. The relevance of this process has been linked to the nucleosynthesis by rapid neutron capture (or r process) in type II supernovae [3][4][5][6], so establishing an accurate rate for the formation of 9 Be is essential for the r-process abundance predictions [7,8].…”

Photodisintegration cross section ofBe9up to 16 MeV in theα + α + nthree-body model

“…The cross section in a lowenergy region has been measured to deduce a production rate of 9 Be from the astrophysical point of view [1][2][3][4][5][6][7]. In the lowenergy region up to E γ = 6 MeV, the cross section has been observed to come from the electromagnetic transitions into the excited states of 9 Be, and theoretically, has been studied within the α + α + n three-body model [8][9][10][11].…”

Formation and decay of resonance states in Be9 and B9 nuclei: Microscopic three-cluster model investigations

“…[24][25][26][27][28][29][30][31], where the structure and different processes taking place in these nuclei have been investigated.…”