Proton total reaction cross sections for 22 isotopes of Ti, Fe, Ni, Cu, Zn, Zr, and Sn at 14.5 MeV

Total proton reaction cross sections have been measured at 14.5 MeV for 22 separated isotope targets to an accuracy of 2% for Ti, Fe, Ni, Cu, Zn, and Zr isotopes and 4% for the Sn isotopes. A beam-attenuation technique employing a solid-state counter to detect elastically scattered protons at forward angles has been used. Use of the solid-state detector reduces the corrections due to inelastic processes to a negligible level. The total reaction cross sections for the Fe, Ni, Zn, and Zr isotopes increase more rapidly with increasing N than optical-model calculations based on 14.5-MeV elastic-scattering and polarization data predict. The measured values for Fe, Ni, Cu, Zn, and Zr isotopes were generally smaller than the optical-model predictions; the measured Sn values, however, were larger. The dip in R near Ni, previously observed using elemental targets in a number of experiments, is reproduced by suitable averaging of the isotope reaction cross sections. The dip is shown to arise from a combination of a sharply rising R with increasing N (for constant Z) and the relatively small average value of N for Ni due to shell closure.