Photodisintegration ofBe9through the1/2+state and cluster dipole resonance

Abstract

Photodisintegration of 9 Be through the 1/2 + state near neutron threshold and cluster dipole resonance below giant dipole resonance was measured with quasi-monochromatic γ-ray beams produced in the inverse Compton scattering of laser photons. The cross section for the 1/2 + state is revisited, being consistent with the 2001 data. The cross section for the cluster dipole resonance is consistent with the cluster dipole sum-rule which however degenerates for the two-body (n-8 Be) and three-body(n-α-α) configurations.

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

“…In particular, the first excited 1/2 + state, observed as a sharp peak just above the 8 Be(0 + ) + n threshold, has attracted much attention, and its structure has been discussed in terms of the three-body resonance of α + α + n [8,9,12] or the two-body virtual state of 8 Be + n [11,13,14]. In the energy region higher than E γ = 6 MeV, the recent measurement [7] reports the photodisintegration cross section of 9 Be up to E γ = 16 MeV, and the cross section shows a significant electric dipole strength below the giant dipole resonance (GDR). An enhancement of a low-lying dipole strength below the GDR has been observed in a wide range of the mass number in neutron-rich nuclei and is often denoted by the pygmy dipole resonance (PDR).…”

“…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].…”

“…On the other hand, 9 Be is a light and stable nucleus which has been found to have a cluster structure, and hence, it is interesting to investigate the mechanism of the dipole strength in 9 Be below the GDR energy region. In a recent measurement [7], Utsunomiya et al showed that the enhanced dipole strength in 9 Be at the excitation energy of ∼8 MeV exhausts 10% of Thomas-Reiche-Kuhn sum rule and almost all the cluster dipole sum rule [7]. We desire to understand the low-lying dipole strength below the GDR comprehensively from a viewpoint of the cluster structure of α + α + n in 9 Be.…”

Photodisintegration cross section of9Be up to Eγ = 16 MeV in the α + α + n three-body model

“…As for the former, a very sharp peak corresponding to the 1/2 + state has been observed at the energy just above the 8 Be+n threshold and our recent investigation is also reported in this meeting by Odsuren [1]. About the second problem, it was reported that the observed dipole strength in 9 Be at the exciation energy of ∼ 8 MeV exhausts 10% of Thomas-Reiche-Kuhn sum rule and almost all the cluster dipole sum rule [2].…”

“…11.3 mb·MeV as a lower limit [2]. It is also suggested that this energy-integrated cross section exhausts 10% of the Thomas-Reiche-Kuhn (TRK) sum rule and almost all of the energy-weighted cluster dipole sum rule.…”