Experimental study of shell effects in the giant resonance in 27Al

Photoproton spectra have been obtained from the 27Al nucleus at 14 bremsstrahlung maximum energies E/sup max//sub γ/ in the range 17.0--29.7 MeV. From the spectra we have calculated the partial cross sections for the photoproton reaction with formation of the final nucleus in the ground state, the first two excited states, and in groups of states with centers of gravity at 4.4, 6.6, 8.5, 11.0, and 13.0 MeV. The sum of the partial cross sections exhausts the total cross section of the (γ,p) reaction. Analysis of the experimental results was carried out simultaneously for the nuclei 27Al, 26Mg, and 28Si with use of data on pickup reactions. The role of nucleons of different shells and the fraction of excitations of the 1p1h type in the 27Al giant dipole resonance are estimated. The influence of the structure of the ground state of nuclei of the 1d-2s shell on the properties of the giant resonance is discussed