Determination of H recoil cross-sections for He ions incident at 2.5–4.5 MeV and recoil angles from 30° to 60°

Proton diAerential recoil cross-sections were measured for impact of He ions in the energy range from 2.5 to 4.5 MeV and for recoil angles from 30∞ to 60∞. For the first time, H recoil cross-sections at angles from 45∞ to 60∞ are reported. All the measured cross-sections, except those for 60∞, deviate from the Rutherford cross-sections. Thin melamine foils (50 lg=cm 2 ) evaporated on50 lg=cm 2 thick Cu were prepared as targets. Two surface barrier detectors positioned at forward angles were used to detect the recoiled and scattered atoms. One detector was kept all the time at 40∞ and was used to measure the loss of H due to irradiation. The experimental results were compared with the other available experimental data for lower recoil angles and a good agreement is found. A comparison is also made with the theoretical calculations obtained by fitting the phase shifts of the kinematic inverse reaction using the principle of detailed balance. Again an agreement is found for low recoil angles, but for 55∞ and 60∞ the experimental cross-sections are significantly smaller than the theoretical values. ” 2001 Elsevier Science B.V. All rights reserved.