Study of ⁷Be Formation from Oxygen Nuclei by Bremsstrahlung Photons at $E_{\gamma }^{{\max }}$ = 40 and 70 MeV

Abstract

Using the induced activity method, the inclusive process ¹⁶O(γ, X)⁷Be of the ⁷Ве isotope photoproduction from oxygen nuclei was studied at the linear electron accelerator AANL (YerPhI) at the boundary energies of bremsstrahlung photons $E_{\gamma }^{{\max }}$ = 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 $E_{\gamma }^{{\max }}$ = 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 ¹⁶O(γ, ⁹Be)⁷Be channel, which proceeds through the two-particle photofission mechanism and the ¹⁶O(γ, n + α + α)⁷Be 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 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”.