Photodisintegration cross section of ${}^9\mathrm{Be}$ up to 16 MeV in the $\alpha + \alpha + n$ three-body model

The photodisintegration of ${}^9\mathrm{Be}$ in the energy region lower than $E_{\gamma }=16$ MeV is investigated by using the $\alpha + \alpha + n$ three-body model and the complex scaling method. The cross section exhibits two aspects in two different energy regions. In the low-energy region up to $E_{\gamma }=6$ MeV, the cross section is explained by the transition strengths into the excited resonant states of ${}^9\mathrm{Be}$, while the dipole transition into the nonresonant continuum states of ${}^8\mathrm{Be}\left(2^{+}\right) + n$ dominates the cross section in the energy region of $6\le E_{\gamma }\le 16$ MeV. Furthermore, it is shown that the dipole strength at $E_{\gamma }\sim 8$ MeV is understood to be caused by the single-neutron excitation from the ${}^8\mathrm{Be}\left(2^{+}\right)\otimes \nu p_{3/2}$ configuration in the ground state.

Figure 1

Schematic picture of energy eigenvalue distribution on the complex energy plane for the $\alpha + \alpha + n$ system.

Figure 2

Energy level diagram in the present calculation in comparison with the experimental data. The levels obtained with $v_3=1.10$ MeV for all the spin-parity states are also presented. The experimental data are taken from Ref. [29].

Figure 3

Calculated photodisintegration cross sections in comparison with the experimental data. The solid squares and open circles represent the experimental data taken from Refs. [6, 7].

Figure 4

Contributions of each spin-parity state in the photodisintegration cross section.

Figure 5

Calculated photodisintegration cross section up to $E_{\gamma }=$ 16 MeV. The solid squares and open circles represent experimental data taken from Refs. [6, 7], respectively.

Figure 6

Contributions of each spin-parity state in the photodisintegration cross section up to $E_{\gamma }=16$ MeV.

Figure 7

Decomposed photodisintegration cross section for the $3/2^{+}$ states.

Figure 8

Same as Fig. 7 but for the $5/2^{+}$ states.