Measurements of theCu63(γ, n)and (γ, 2n) Cross Sections

The ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}(\gamma , n)$ cross section was measured over the energy range from threshold to 25 MeV with a photon beam of 2.0% resolution which was produced by the inflight annihilation of positrons. The ($\gamma , n$) cross section was found to have a maximum value of 75±6 mb at about 17.1 MeV and an integrated value up to 25 MeV of 490±40 MeV mb. No structure was observed in these measurements or in additional ($\gamma , n$) measurements which were made in the region of the peak of the giant resonance with 1.5% $\gamma$-ray resolution. The ($\gamma , n$) data from the present experiment were combined with the $(\gamma , n)+(\gamma , pn)$ data from Livermore to obtain the ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}(\gamma , pn)$ cross section, which was found to have a maximum value of 15±4 mb at about 23 MeV and an integrated value up to 25 MeV of 60±15 MeV mb. In addition, the ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}(\gamma , 2n)$ cross section was measured at three representative energies between threshold and 26 MeV. The maximum ($\gamma , 2n$) cross section obtained was 10.0±1.6 mb at 23.7 MeV. The results of the experiments are compared with previous measurements and with theory. A small bump in the $(\gamma , n)+(\gamma , pn)+(\gamma , 2n)$ cross section at about 23 MeV may possibly be attributed to an analog giant resonance.