A general expression for the width of a charged-particle track

Theoretical estimates of the dimensions of charged-particle tracks are conventionally based on Monte Carlo simulation of the trajectories of the primary as well as all secondary particles. The present note expresses the lateral width of a track by an integral over the primary cross-section and thus eliminates the need for simulating the primary trajectory. Expressions are given for the second-order and the fourth-order lateral average over the deposited-energy profile. These relations are applicable to tracks generated by either ionization or collision cascades. As an illustration, an analytical estimate is presented for the width of a collisional track generated by Au ions in Au which is of interest in current experimental work on sputtering by gold clusters. (C) 2000 Elsevier Science B.V. All rights reserved.