Abstract
In the present work, we study the Timepix2 pixels’ high energy response in the so-called adaptive gain mode. Therefore, Timepix2 with a 500 μm thick silicon sensor was irradiated with ...protons of energies in the range from 400 keV to 2 MeV and
α
-particles of 5.5 MeV from
241
Am. A novel method was developed to determine the energy deposit in single pixels of particle imprints, which are spread out over a set of neighbor pixels (cluster). We show that each pixel is capable of measuring the deposited energy from 4 keV up to ∼3.2 MeV. Reconstructing the full energy content of the clusters, we found relative energy resolutions (
σ
E
) better than 2.7% and better than 4% for proton and
α
-particle data, respectively. In a simple experiment with a 5.5 MeV
α
-particle source, we demonstrate that energy losses in thin (organic) specimen can be spatially resolved, mapping out sample thickness variations, with a resolution around 1–2 μm, across the sensor area. The inherent spatial resolution of the device was determined to be 350 nm in the best case.
A micro-SPECT system having spatial resolution of 2.5 mm is presented. The system has a field of vision about 57 × 57 mm. Results of tomographic reconstruction of calibration phantoms using Tc-99m ...solution are outlined. The design of phantoms that can be used to assess performance of SPECT system having a narrow field of vision is given.
–
This paper describes the methodology and measurements results of the micro-SPECT system parameters with a 57 × 57 mm field of view. The system detection efficiency and uniformity of the Timepix ...based micro-SPECT system is measured using a
99m
Tc radioactive source. The system detection efficiency is 81%, while the total efficiency is 0.0038% only, mainly due to the small surface of the detector. The intrinsic uniformity is 92%. The integral and differential uniformity are 44 and 84%, respectively. The integral uniformity can be significantly improved by using additional filters and more advanced decoding algorithms that take into account the geometry of the collimator.
The Medipix detector family with single photon counting, photon energy discrimination and small pixel size makes it possible to carry out spectral X-ray imaging with high spatial resolution. In these ...detectors, the energy discrimination is performed independently in each pixel. For a good quality of spectral measurements, it is important that the globally defined energy threshold corresponds to the same energy in each pixel. The possibility of local adjustment of the pixel threshold is implemented by the chip design. In this paper, we present a method for thresholds equalization at an arbitrary energy using the X-ray tube spectrum high energy cut-off as a reference energy point. It is shown that the proposed method reduces the spread of pixel energy thresholds by more than 60 % in the energy range from 15 keV to 55 keV.
Abstract
Fast, incremental evolution of physics instrumentation raises the question of efficient software abstraction and transferability of algorithms across similar technologies. This contribution ...aims to provide an answer by introducing Track Lab, a modern data acquisition program focusing on extensibility and high performance. Shipping with documented API and more than 20 standard modules, Track Lab allows complex analysis pipelines to be constructed from simple, reusable building blocks. Thanks to multi-threaded infrastructure, data can be clustered, filtered, aggregated and plotted concurrently in real-time. In addition, full hardware support for Timepix2, Timepix3 pixel detectors and embedded photomultiplier systems enables such analysis to be carried out online during data acquisition. Repetitive procedures can be automated with support for motorized stages and X-ray tubes. Freely distributed on 7 popular operating systems and 2 CPU architectures, Track Lab is a versatile tool for high energy physics research.
Hybrid pixel detectors based on the Medipix chips have proven themselves as a good tool for spectral X-ray imaging. An important advantage of such detectors is the possibility to use various sensor ...materials (Si, GaAs:Cr, CdTe etc). Each of these materials has own advantages and disadvantages. The higher Z materials provide the higher photon registration efficiency, but also the greater energy of the fluorescent photons distorting the detector's energy response. The thickness of the sensor affects the same way: the thicker sensor means the higher photon registration efficiency, but the energy resolution gets worse. At the same time, photons that have passed through the detector without interacting in it can be registered by the next detector. The combination of several detectors with various sensor materials allows increasing the overall photon registration efficiency. In this case, each detector will operate in the optimal energy range. In this work, we consider a system based on three Timepix detectors with sensors made from Si, GaAs:Cr and CdTe. The Monte Carlo simulation was used for the sensors thickness optimization. The possibility and advantages of using such imaging system for spectral CT are demonstrated.
Abstract
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
μ
e
τ
e
¯
= 1.3 × 10
−3
cm
2
/V with a standard deviation
σ
= 0.4 × 10
−3
cm
2
/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) cm
2
/V/s and
τ
e
= (1.38 ± 0.31)
μ
s. 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
μ
m within the sensor volume and a particle trajectory measurement precision Δ
xyz
= 100
μ
m, at a distance of 1 m from the sensor. We demonstrate by measurement with a
22
Na 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).
Hybrid pixel semiconductor detectors find more and more applications in modern experimental physical setups. In particular, pixelated detectors based on GaAs:Cr sensor and Timepix3 chip are used in ...R&D for a state-of-the-art Transition Radiation Detector prototype at CERN. Motivation and usage aspects for GaAs:Cr-Timepix3 device in the experiment are covered in the talk. Authors" contribution to the work of the research group is a study of charge collection and transportation processes in the sensor including fluorescence and so-called charge sharing effect. These are able to significantly affect both spatial and energy resolution of the system. Estimates for the effects are obtained via numerical modelling and then used to analyze the impact on the detector performance.
Abstract
Timepix3 pixel detectors have demonstrated great potential for tracking applications. With 256 × 256 pixels, 55 µm pitch and improved resolution in time (1.56 ns) and energy (2 keV at 60 ...keV), they have become powerful instruments for characterization of unknown radiation fields. A crucial pre-processing step for such analysis is the determination of particle trajectories in 3D space from individual tracks. This study presents a comprehensive comparison of regression methods that tackle this task under the assumption of track linearity. The proposed methods were first evaluated on a simulation and assessed by their accuracy and computational time. Selected methods were then validated with a real-world dataset, which was measured in a well-known radiation field. Finally, the presented methods were applied to experimental data from the Large Hadron Collider. The best-performing methods achieved a mean absolute error of 1.99° and 3.90° in incidence angle
θ
and azimuth
φ
, respectively. The fastest presented method required a mean computational time of 0.02 ps per track. For all experimental applications, we present angular maps and stopping power spectra.
Abstract
The response of a Timepix3 (256 × 256 pixels, pixel pitch 55 μm) detector with a 500 μm thick HR GaAs:Cr sensor was studied in proton beams of 125 MeV at the Danish Centre for Particle ...Therapy in Aarhus, Denmark and in a 120 GeV/
c
pion beam at the Super-Proton Synchrotron (SPS) at CERN. The sensor was biased at different voltages and irradiated at different angles. The readout chip was configured to operate in electron and hole collection modes. Measurements at grazing angles allowed to see elongated tracks with well-defined impact and exit points, so that charge carrier production depths could be determined in each pixel. We extracted the charge collection efficiencies and the charge carrier drift times as a function of the distance to the pixel plane. It was found that measured proton tracks are shorter in hole collection than in the case of electron collection, which is explained by the shorter lifetime of holes. At an angle of 60 degrees with respect to the sensor normal, the average track length in hole collection was ∼700 μm and 950 μm in electron collection mode. To understand the experimental findings, models describing the properties of HR GaAs:Cr were implemented into the Allpix
2
simulation framework. We added previously presented experimental results describing the dependence of the electron drift velocity on the electric field and validated the response by comparing measurement and simulation for various X- and gamma-ray sources in the energy range of 10–60 keV. By comparison of the experimental and the simulated results, the mobility
μ
h
and the lifetime of holes
τ
h
were estimated as
μ
h
= (320 ± 10) cm
2
/V/s and
τ
h
= (4.5 ± 0.5) ns.
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