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

Proton differential recoil cross-sections were measured for impact of He io ns in the energy range from 2.5 to 4.5 MeV and for recoil angles from 30 de grees to 60 degrees. For the first time, H recoil cross-sections at angles from 45 degrees to 60 degrees are reported. All the measured cross-sections , except those for 60 degrees, deviate from the Rutherford cross-sections. Thin melamine foils (similar to 50 mug/cm(2)) evaporated on similar to 50 m ug/cm(2) thick Cu were prepared as targets. Two surface barrier detectors p ositioned at forward angles were used to detect the recoiled and scattered atoms. One detector was kept all the time at 40 degrees and was used to mea sure the loss of H due to irradiation. The experimental results were compar ed with the other available experimental data for lower recoil angles and a good agreement is found. A comparison is also made with the theoretical ca lculations obtained by fitting the phase shifts of the kinematic inverse re action using the principle of detailed balance. Again an agreement is found for low recoil angles, but for 55 degrees and 60 degrees the experimental cross-sections are significantly smaller than the theoretical values. (C) 2 001 Elsevier Science B.V. All rights reserved.