The rate of formation of extended defects by heavy energetic ions in track-forming minerals shows a pronounced nonlinear dependence on the linear ionization rate. It is suggested that the formation of an extended defect—as recorded by small-angle x-ray scattering—requires a certain threshold ionization density. As a consequence, the mean number of observable defects per ion track is related more directly to the fluctuation in ionization density than to its mean value.

• Received 13 June 1985

DOI:https://doi.org/10.1103/PhysRevB.32.5429