γ -ray emission in α -particle interactions with C, Mg, Si, and Fe at Eα=50-90 MeV

Abstract

Nuclear deexcitation lines are regularly observed in the γ-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and α particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the γ-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the γ-ray emission in interactions of α-particle beams of Eα=50-90 MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one LaBr3:Ce detector have been employed to detect the γ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt γ-ray emission from the targets from other γ rays and neutron-induced background. γ-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, C12, Mg24, Si28, Fe56, there are now measured cross-section data from reaction threshold to Eα=90 MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong γ-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range