Study of 7 Be Formation from Oxygen Nuclei by Bremsstrahlung Photons at E_γ^max = 40 and 70 MeV

Using the induced activity method, the inclusive process 16 O(γ, X) 7 Be of the 7 Ве isotope photoproduction from oxygen nuclei was studied at the linear electron accelerator AANL (YerPhI) at the boundary energies of bremsstrahlung photons E_γ^max = 40 and 70 MeV. This process was first observed in the near-threshold energy range E γ < 40 MeV in this work owing to low-background conditions in the underground laboratory of the AANL where spectroscopic measurements were carried out. The cross-section averaged over the spectrum of bremsstrahlung photons and the cross-section per equivalent photon has been measured. Estimates are also obtained for the integral cross-section of this process. The measured cross-sections are compared with the available experimental data and predictions of the TALYS1.9, GEANT4, and FLUKA models. It is shown that the predictions of TALYS and GEANT4 are strongly underestimated (especially at E_γ^max = 40 MeV) as compared with our data, which is associated with a strong underestimation in model computations of the role of two main near-threshold reaction channels: the 16 O(γ, 9 Be) 7 Be channel, which proceeds through the two-particle photofission mechanism and the 16 O(γ, n + α + α) 7 Be spallation channel. The FLUKA predictions are qualitatively comparable with experimental data at E γ < 40 MeV and E γ = (50–60) MeV, however, they greatly exceed them in the energy range E γ = (40–50) MeV, this excess is almost entirely caused by the overestimated contribution of the 16 O(γ, n + α + α) 7 Be spallation reaction cross-section. The data obtained may turn out to be useful in attempts to improve theoretical models of nuclear reactions, in the study of the radioisotope content of the earth’s atmosphere, and also be of interest in connection with the so-called “primary lithium problem”.