Measurement of the energy resolution and calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip

This paper describes an iterative method of per-pixel energy calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip. A convolution of precisely measured spectra of characteristic X-rays of different metals with the resolution and the efficiency of the pixel detector is used for the calibration. The energy resolution of the detector is also measured during the calibration. The use of per-pixel calibration allows to achieve a good energy resolution of the Timepix detector with GaAs:Cr sensor: 8% and 13% at 60 keV and 20 keV, respectively

Characterization of a 5 mm thick CZT-Timepix3 pixel detector for energy-dispersive γ -ray and particle tracking

The present manuscript describes a comprehensive characterization of a novel highly segmented 5 mm CZT sensor attached to Timepix3. First, the sensor’s IV curve was measured and basic sensor characterization was done with laboratory γ-radiation sources. The sensor resistivity was determined to be (0.155± 0.02) GOhm · cm. The sensor showed decent homogeneity, both for the per-pixel count rate and electron mobility-lifetime product μ e τ e. The latter was measured to be μeτe¯ = 1.3 × 10−3 cm2/V with a standard deviation σ = 0.4 × 10−3 cm2/V describing the dispersion of values for different pixels. The basic sensor characterization is complemented by measurements at grazing angle in a 120 GeV/c at the CERN’s Super Proton Synchrotron. The penetrating nature of these particles together with the pixelation of the sensor allows for a determination of the charge collection efficiency (CCE), as well as charge carrier drift properties (drift times, lateral charge cloud expansion) as a function of the interaction depths in the sensor. While CCE drops by 30%–40% towards the cathode side of the sensor, from the drift time dependency on interaction depth, the electron mobility μ e was extracted to be (944.8 ± 1.3) cm2/V/s and τ e = (1.38 ± 0.31) μs. The spectroscopic performance was assessed in photon fields and extracted from energy loss spectra measured at different angles in the pion beam. While at photon energies below 120 keV incomplete charge collection leads to an underestimation of the photon energy when irradiated from the front-side, at higher energies the relative energy resolution was found to be ∼4.5%, while a relative energy resolution of ∼7.5% was found for the particle energy loss spectra. It is shown that the drift time information can be used to reconstruct particle interactions in the sensor in 3D, providing a spatial resolution of σ xyz = 241 μm within the sensor volume and a particle trajectory measurement precision Δxyz = 100 μm, at a distance of 1 m from the sensor. We demonstrate by measurement with a 22Na source, that the energy resolution combined with the 3D reconstruction allows for detection of γ-ray source location and polarity using Compton scattering within the sensor (Compton camera and scatter polarimeter)

Alignment and resolution studies of a MARS CT scanner

This paper describes a procedure of alignment of MARS CT scanner with cone beam geometry. The position of the xray source relative to the detector, the tilt of the detector are measured during alignment. The mechanical precision of gantry movement is determined. Significant improvement in the quality of image reconstruction has been achieved as a result of the calibration. Spatial resolution (PTF) of the scanner is confirmed to be about 30 μm

Measurement of shower development and its Moli\`ere radius with a four-plane LumiCal test set-up

A prototype of a luminometer, designed for a future e+e- collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this beam test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Moli\`ere radius has been determined to be 24.0 +/- 0.6 (stat.) +/- 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.Comment: Paper published in Eur. Phys. J., includes 25 figures and 3 Table

Performance of fully instrumented detector planes of the forward calorimeter of a Linear Collider detector

Detector-plane prototypes of the very forward calorimetry of a future detector at an e+e- collider have been built and their performance was measured in an electron beam. The detector plane comprises silicon or GaAs pad sensors, dedicated front-end and ADC ASICs, and an FPGA for data concentration. Measurements of the signal-to-noise ratio and the response as a function of the position of the sensor are presented. A deconvolution method is successfully applied, and a comparison of the measured shower shape as a function of the absorber depth with a Monte-Carlo simulation is given.Comment: 25 pages, 32 figures, revised version following comments from referee