Rigidity Dependence of the Interplanetary Mean Free Path

Abstract

We use energy spectra of anomalous cosmic rays derived from data from experiments on the Voyager and Pioneer spacecraft to inf er the rigidity dependence of the perpendicular interplanetary mean free path over the rigidity range ~0.3 to 4 GV. Data are from three intervals: 1993/157-209, 1994/157- 313, and l 996/1-52. We use two techniques to estimate that the rigidity dependence is approximately proportional to R^2 at low rigidities with a flattening above ~1 GV, roughly consistent with recent theoretical estimates (Bieber et al. 1995).