Bending MeV proton beams in graded composition Si1-xGex/Si layers

This paper characterises the ability of graded composition Si1-xGex/Si bila yers to bend MeV proton beams through small angles. The graded germanium ep ilayer composition results in off-normal lattice directions of the epilayer being gradually bent, so channeled protons are gently deflected away from their initial direction. The relationship between the incident beam energy, bilayer tilt angle, emergent angle and bending efficiency for 3, 5 and 10 MeV protons are simulated using a Monte Carlo channeling code and studied e xperimentally using the Utrecht magnetic spectrometer. A maximum bending ef ficiency of 35% of those protons, which are channeled at the front surface of the epilayer is measured with the bilayer in a reverse geometry, and goo d agreement with simulated results is demonstrated. These results are used to predict the bending behaviour at higher beam energies and the relevant o ptimum layer characteristics. (C) 2000 Elsevier Science B.V. All rights res erved.