ELASTIC-SCATTERING CROSS-SECTIONS OF PROTONS BY COPPER, MOLYBDENUM, SILVER AND TIN NEAR THE COULOMB BARRIER

Cross sections for elastic scattering of protons by natural copper, mo lybdenum, silver and tin have been measured in the energy range of 2.3 -6.5 MeV at typical Rutherford backscattering angles of 135 degrees an d 165 degrees. 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 molybdenu m, 5.0 and 5.8 MeV for silver, and 6.1 and 6.2 MeV for tin at angles o f 135 degrees and 165 degrees, respectively. Resonances or the rapid d ecrease of the cross sections above the thresholds render practical pr oton 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 an d theoretical interest has recently been focused at the non-Rutherford cross sections. Comparing the experimental non-Rutherford threshold e nergies with theoretical calculations, we find the data clearly exceed ing the predictions of simple classical formulations, while the optica l model approach yields more realistic threshold energy values. (C) 19 98 American Institute of Physics. [S0021-8979(98)07016-9]