Evaluation of Timepix2 in adaptive gain mode for stopped and penetrating position-sensitive ion spectroscopy

Abstract

We present the study of the response of a Timepix2 detector (256 × 256 pixels, pixel pitch 55 µm) with a 500 µm thick silicon sensor in laboratory measurements with α sources, charged particle beams of relativistic ion fragments at the Super-Proton-Synchrotron at CERN and in short-ranged heavy ion beams at the Heavy Ion Facility of UCLouvain in Belgium: 22Ne, 53Cr and 103Rh of 238, 505 and 957 MeV, respectively. The Timepix2 detector was used in adaptive gain mode, and calibrated using previously developed methodology using protons with energies in the range from 500 keV to 2 MeV and α-particles of 5.5 MeV from 241Am source prior to the testing. In a laboratory experiment, the detector was irradiated with α-particle from a 239Pu241Am244Cm source. α-particles of higher energy (∼ 9 MeV) were obtained through a measurement of naturally occurring decays of radon and its daughters while the detector was left running in the laboratory for two weeks. In both cases, an energy resolution of 2% was achieved. In the stopped ion beam measurement, the proper ion energy determination was hindered by the per-pixel saturation of 3.2 MeV. Still, due to an increase of measured energy with increasing charge deposition, the different ion species were separable. In the last study, the dE/dX spectra were obtained in a mixed relativistic particle beam and used to evaluate the capability of determining the beam composition. The spectrum stripping technique using iterative Landau curve fitting was applied to the spectra allowing for ion charge determination up to Z = 13. The per-pixel saturation was mitigated by placing the detector at an angle of 70 degrees with respect to the sensor normal.