Cross Sections for theO16(γ,π+)N16Reaction

Abstract

Cross sections for the ${\mathrm{O}}^{16}(\gamma ,{\pi }^{+}){\mathrm{N}}^{16}$ reaction were determined by measuring the ${\mathrm{N}}^{16}$ radioactivity produced in water samples that were irradiated with bremsstrahlung of maximum energy varying from 100 to 300 MeV. The observed yields were corrected for contributions from photonuclear reactions involving the ${\mathrm{O}}^{17}$ and ${\mathrm{O}}^{18}$ nuclei present in the targets and for secondary reactions. The resulting cross sections reach a maximum value of 8 μb at 240 MeV. The ${\mathrm{O}}^{16}(\gamma ,{\pi }^{+}){\mathrm{N}}^{16}$ cross sections average about 24% of those reported previously for the ${\mathrm{B}}^{11}(\gamma ,{\pi }^{-}){\mathrm{C}}^{11}$ reaction. These results are in agreement with those expected from the theory outlined by Laing and Moorhouse for reactions of this type assuming surface production of pions and assuming that the transition probabilities depend much more on the total number of states available than on the specific details of the states involved.