High-energy per-pixel calibration of timepix pixel detector with laboratory alpha source

The spectral response of the pixel detector Timepix at the high per-pixel proportional range is examined and calibrated using a simple technique and alpha particles from a standard laboratory source in air. For the detector used, a Timepix ASIC chip equipped with a 300 mu m thick silicon sensor, the spectral range is newly extended up to about 1750 keV per-pixel. This expands and covers the region above 850 keV per pixel which is described and covered by the existing low-energy calibration. The low-energy calibration uses discrete low-energy gamma rays in the range 5-60 keV and is extrapolated over the linear range up to 850 keV/px. Above this level, the per-pixel spectral response changes. At higher energies it undergoes distortion and saturation. The proportional and monotonic response is observed with regions of varying dependence up to nearly 2 MeV. This high-energy region is covered and described by the newly developed calibration method which Uses an alpha source of common low activity (kBq level). Data are collected within one day of total measuring time. Measurements are performed in air at various source-to-distance positions and several sensor bias settings. The developed method together with suitable setting of the sensor bias, which determines the extent of charge sharing, expands the spectral response of Timepix to high energy-loss particles such as alpha particles and light ions in wide energy range. Results are demonstrated on alpha particles, protons and C-12 ions. Resulting spectra of deposited energy and cluster pixel height are correctly calibrated and they reproduce expected values.