Initial results on charge and velocity discrimination for heavy ions using silicon-Timepix detectors

Abstract

The Timepix ASIC is a version of the hybrid pixel detector technology developed by the Medipix2 Collaboration [1]. Within the 256 by 256 pixel matrix, the electronics for each of the 55μm individual pixels are contained in the footprint of that pixel. The Timepix has a charge-sensitive pre-amp and an associated discriminator attached to a logic unit capable of being employed in one of several different modes. For the present work, the Time-Over-Threshold mode was used to allow measurement of deposited energy in the silicon sensor layer. The general properties of a Timepix-based device with a silicon sensor have been described in [2,3], and [4].Ionization along heavy ion particle tracks in the silicon sensor results in the production of free charge carriers in the detector. The charge carrier motion under the influence of an applied bias voltage leads to charge collection at the Timepix-sensor interface in one or more pixels. Signatures within the pixel cluster patterns are currently being examined, and initial results indicate that such signatures, when coupled with stopping power information, provide enough discrimination capability to begin to resolve heavy ion charge and velocity. Here we present the salient characteristics that have been identified for heavy ion charge and velocity discrimination using Timepix Silicon detectors and discuss the application of this method for particle track characterization.