THE STUDIES OF NON-RUTHERFORD BACKSCATTERING CROSS SECTIONS OF ⁴He FROM ¹⁶O

In this article, we report the 170° backscattering cross sections of ⁴He from ¹⁶O in the energy range of 2.0-9.0 MeV. Our measurements show that the alpha-oxygen scattering remains Rutherford scattering up to E_\alpha=2.35 MeV, and there exist two energy regions, namely 5.55-5.85MeV and 8.50-8.80MeV, where the cross sections are enhanced and show a smooth variation. The measured laboratory cross sections are 9.50-9.97 and 35.0-33.0 times greater than the Rutherford values, respectively. In the 8.50-8.80MeV region, the cross sections at scattering angles of 160°, 165°, 170° and 175° were measured and found to be strongly angle-dependent. A most strong resonance occurred at 7.60 MeV, where the cross section is 200 times of its Rutherford value. This resonance has been used to measure the ¹⁶O concentration on a Cu surface, with a sensitivity of 1×10¹⁵ oxygen atoms/cm², Besides, we have studied the backscattering angle dependence of the threshold energy, i.e., the energy at which the elastic cross section begins to deviate from its Rutherford value. The experimental result seems not in agreement with the prediction made from the analytical formula developed by Bozoian et al.