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

Yields of7Be,10Be,22Na,24Na and28Mg produced fromnatB,natC,natO,23Na,27Al,natSi,natS,natCl,natK,natCa,natV,55Mn,natFe,59Co,natNi,natCu,89Y,natAg,natIn,141Pr,159Tb,165Ho and197Au in irradiations with bremsstrahlung having maximum end-point energies up to 1200 MeV were measured by γ-ray spectrometry (7Be,22Na,24Na and28Mg) and accelerator mass spectrometry (10Be). The yields of heavier fragments,39Cl,43, 44m, 44g, 46, 47, 48Sc,59Fe, and56, 57, 58, 60Co, 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 mass-dependence 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.