  The response of the Timepix detector to neon ions with kinetic energy 77 and
158.4 MeV has been studied at the cyclotron U-400M of the JINR Flerov
Laboratory of Nuclear Reaction. Sensors produced from gallium arsenide
compensated by chromium and from silicon are used for these measurements. While
in Timepix detector with Si sensor the well-known so-called "volcano effect"
observed, in Timepix detector with GaAs:Cr sensor such effect was completely
absent.
  In the work the behavior of the Timepix detector with GaAs:Cr sensor under
irradiation with heavy ions is described in comparison with the detector based
on Si sensor. Also the possible reason for absence of "volcano" effect in
GaAs:Cr detector is proposed.
