Study of ⁷Be formation from oxygen nuclei by Bremsstrahlung photons at Eγmax = 40 and 70 MeV

Using the induced activity method, the inclusive process 16^O(γ, X)⁷Be of the ⁷Be 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 in the near-threshold energy range Eγ <40 MeV was first observed 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 have 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 with the 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) in comparison with our data, which is associated with a strong underestimation in model calculations of the role of two main near-threshold reaction channels: the ¹⁶O(γ, ⁹Be)⁷Be channel, which proceeds through the two-particle photofission mechanism and the ¹⁶O(γ, n+α+α)⁷Be spallation channel. FLUKA predictions are qualitatively comparable with experimental data at Eγ < 40 MeV and E_γ = (50–60) MeV, however, they greatly exceed them in the energy range E_γ = (40–50) MeV, this excess being almost entirely due to the overestimated contribution of the ¹⁶O(γ, n+α+α)⁷Be 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'