Partial photonucleon cross sections and the 24Mg giant dipole resonance

Abstract

The ( γ, n i ) cross sections in the region of the giant dipole resonance (GDR) of the self-conjugate 24Mg nucleus have been obtained on the basis of the experimental ( γ, p i ) cross sections ( i specifies states of the final nucleus) and the isospin symmetry of photonucleon decays. In the ( γ, n i ), ( γ, p i ) cross sections, the total photonucleon cross sections, and the photoabsorption cross sections, we have identified the components due to semidirect GDR decay using the ratios of the semidirect decay widths resulting from the R-matrix theory. In the integrated photoabsorption, photoproton, and photoneutron cross sections the probability of semidirect decays was found to be 57–67%, 45–60%, and 80–90%, respectively. The semidirect decays dominate in the low-energy (<22 MeV) group of the GDR containing the transitions 1 d2 s → 1 f2 p and 1 p 1 2 → 1 d2 s and the statistical decays dominate in the high-energy (> 22 MeV) group of the transitions 1 p 3 2 → 1 d2 s .