Elastic scattering cross sections of protons by copper, molybdenum, silver and tin near the Coulomb barrier

Abstract

Cross sections for elastic scattering of protons by natural copper, molybdenum, silver and tin have been measured in the energy range of 2.3–6.5 MeV at typical Rutherford backscattering angles of 135° and 165°. The threshold energies have been determined above which the Rutherford cross sections become invalid. The threshold energies obtained are 3.5 and 3.4 MeV for copper, 5.1 and 5.0 MeV for molybdenum, 5.0 and 5.8 MeV for silver, and 6.1 and 6.2 MeV for tin at angles of 135° and 165°, respectively. Resonances or the rapid decrease of the cross sections above the thresholds render practical proton backscattering analysis impossible. A literature survey has been carried out to compile relevant energy threshold data for the present target mass and scattering angle regions. Considerable experimental and theoretical interest has recently been focused at the non-Rutherford cross sections. Comparing the experimental non-Rutherford threshold energies with theoretical calculations, we find the data clearly exceeding the predictions of simple classical formulations, while the optical model approach yields more realistic threshold energy values.