Time-of-flight system for profiling recoiled light elements

Abstract

The Elastic Recoil Detection method developed at University of Montreal to profile light elements in solids has been improved significantly. In this method, the light elements are ejected out of the sample by an incident 30 MeV 35Cl beam. In the original technique, the concentration profiles are extracted from the energy spectra of the recoiling particles. Some ambiguity occurs when two or more recoil particles have the same energy. This problem can be solved using a time-of-flight technique to measure the masses of the recoil particles. We use a thin carbon foil and a micro-channel plate as a start detector and a Si detector as a stop detector. This system gives a time resolution of 250 ps fwhm for 5.48 MeV alpha particles. It has been used successfully to separate the profiles of H, B, C, N and O. This method should prove useful to complement the profiles of heavy elements obtained by RBS.