Target-dependence of light fragment production in photonuclear reactions at intermediate energies

Abstract

in irradiations with bremsstrahlung having maximum end-point energies up to 1200 MeV were measured by γ-ray spectrometry ( 7 Be, 22 Na, 24 Na and 28 Mg) and accelerator mass spectrometry ( 10 Be). The yields of heavier fragments, 39 Cl,43, 44m, 44g,46,47, 48 Sc, 59 Fe,and 56,57,58,60 Co, were also measured by γ-ray spectrometry in order to survey the relative contribution of fragmentation to spallation and/or fission in the mass yield curves. A distinct difference of the target massdependence of these yields has made it possible to disentangle the contributions of photospallation and photofragmentation processes. It was found that the neutron-to-proton ratios of targets strongly affect the formation of the nuclei by fragmentation as revealed in the yields of the isotopic pairs as well as of the single isotopes. The photon results were compared with those of proton-induced reactions, and no clear effect due to the difference of the initial interactions of photons and protons with nuclei was found in the fragment yields.

Photonuclear channel of 7Be production in the Earth’s atmosphere

“…At the present time the monitoring of the content of radionuclides in the bottom layer of the Earth's atmosphere leads to the conclusion that the short-lived isotope 7 Be of cosmogenic origin makes a substantial contribution to the radioactivity of air in this layer. The change in the content of 7 Be in air stems from the solar activity and have characteristic seasonal variations and a latitude dependence [1,2].…”

“…These are the so-called spallation reactions 14 N(p, X) 7 Be, 16 O(p, X) 7 Be, 14 N(n, X) 7 Be, and 16 O(n, X) 7 Be. Photonuclear reactions may be yet another mechanism of the production of the beryllium isotope 7 Be in the upper atmosphere [5].…”

“…Unfortunately, there are very few data in the literature on the reactions of multiparticle photodisintegration of nuclei. For example, the cross section for the reaction 12 C(γ, nα) 7 Be was studied in detail in [6]. The reaction nat O(γ, X) 7 Be on the natural mixture of oxygen isotopes in the energy range from 300 to 1000 MeV was studied in [7].…”

“…For example, the cross section for the reaction 12 C(γ, nα) 7 Be was studied in detail in [6]. The reaction nat O(γ, X) 7 Be on the natural mixture of oxygen isotopes in the energy range from 300 to 1000 MeV was studied in [7]. The average value of the cross sections for this photonuclear reaction in the above energy range is about 0.3 mb.…”

“…An experiment in which some targets, including oxygen, nitrogen, and carbon, were irradiated with bremsstrahlung photons at a linear electron accelerator was performed in order to determine the cross sections for 7 Be photoproduction in the reactions 12 C(γ, X) 7 Be, 14 N(γ, X) 7 Be, and 16 О(γ, X) 7 Be. The energy of accelerated electrons was 90 MeV, and their current was 3.26 μA.…”