Timepix Chip Research Articles

Scintillator-based Timepix3 detector for neutron spin-echo techniques using intensity modulation.

A scintillator-based Timepix3 (TPX3) detector was developed to resolve the high-frequency modulation of a neutron beam in both spatial and temporal domains, as required for neutron spin-echo experiments. In this system, light from a scintillator is manipulated with an optical lens and is intensified using an image intensifier, making it detectable with the TPX3 chip. Two different scintillators, namely, 6LiF:ZnS(Ag) and 6LiI:Eu, were investigated to achieve the high resolution needed for spin-echo modulated small-angle neutron scattering (SEMSANS) and modulation of intensity with zero effort (MIEZE). The methodology for conducting event-mode analysis is described, including the optimization of clustering parameters for both scintillators. The detector with both scintillators was characterized with respect to detection efficiency, spatial resolution, count rate, uniformity, and γ-sensitivity. The 6LiF:ZnS(Ag) scintillator-based detector achieved a spatial resolution of 200μm and a count rate capability of 1.1 × 105 cps, while the 6LiI:Eu scintillator-based detector demonstrated a spatial resolution of 250μm and a count rate capability exceeding 2.9 × 105 cps. Furthermore, high-frequency intensity modulations in both spatial and temporal domains were successfully observed, confirming the suitability of this detector for SEMSANS and MIEZE techniques, respectively.

Probability distribution maps of deposited energy with sub-pixel resolution for Timepix3 detectors

The Medipix3 Collaboration has developed the Timepix3 chip, which can provide information about individual particles interacting with a hybrid pixelated semiconductor detector. The Timepix3 generates a data packet including time and energy information for each pixel receiving a charge above the discriminator threshold. From a set of such packages generated by one particle the total deposited energy and the sub-pixel center of mass (c.m) position of the interaction can be calculated. However, sub-threshold losses will distort both the measured energy and c.m calculation. This work aims to generate probability maps for the most probable initial interaction position and energy for a given detected cluster. The correction maps were calculated for different energies and sub-pixel c.m positions. It is crucial to realistically simulate the front-end response of the Timepix3 detector to be able to match and understand the experimental data and generate accurate probability maps. The correction maps from the simulations using the simulation tool Allpix 2 are applied to experimental data utilizing an Am-241 source to irradiate a Minipix Timepix3, leading to sub-pixel resolution and improved energy resolution for Timepix3 detectors.

Measurement of electron fluxes in a Low Earth Orbit with SATRAM and comparison to EPT data

We present the determination of electron fluxes measured by the Space Application of Timepix Radiation Monitor (SATRAM), a pixelated single-layer particle detector and the comparison with the Energetic Particle Telescope (EPT), a science-class radiation spectrometer. Both are attached to the Proba-V satellite of the European Space Agency. SATRAM hosts a Timepix chip with a 300 μm thick silicon sensor divided into a 256 × 256 pixel matrix with 55 μm pixel pitch. Simulations were conducted to determine the geometric factor of the sensor and the effective area that includes the shielding effects from all directions. The simulation was further used to study the influence of secondary particle production, track interruption, and backscattering on the number of detected particles. Particle identification is performed using two different methods. The first method requires that particle tracks are individually identifiable. A neural network was developed for this purpose, achieving an accuracy of 90.2% for particle identification. If individual particle tracks could not be identified, a statistical approach was used utilizing the energy deposition, average cluster energy, and the last known fraction of electrons. A comparison of the two instruments shows good agreement within one order of magnitude for the majority of the data.

Tristan10M detector: characterization of a large area detector for time resolved experiments based on Timepix3 chip

Tristan10M is a 10-million-pixel large area detector based on the Timepix3 ASIC. The Timepix3 ASIC can work in event driven mode in addition to the standard frame based mode. Thanks to these capabilities of the Timepix3 ASIC, the Tristan detector is ideal for time-resolved experiments. The Tristan 10M detector is organized in a 2 × 5 module matrix, each module being made up of sixteen Timepix3 chips bump-bonded to a monolithic pixelated silicon sensor. In this contribution, we will report on the status of the detector development, and characterization results in terms of threshold equalization, energy calibration, and flat-field correction. A number of initial commissioning experiments have been carried out on the small molecule single crystal diffraction beamline I19 at Diamond light source, which we will also report on here. In particular, X-ray powder diffraction from a standard sample, LaB6, was performed to evaluate the inter-module alignment based on per-module basis.

A New Technique Based on Convolutional Neural Networks to Measure the Energy of Protons and Electrons With a Single Timepix Detector

The Timepix chip has been exposed to the outer space for the first time with the Space Application of Timepix-based Radiation Monitor (SATRAM) instrument on Project for On-Board Autonomy Vegetation (Proba-V), a European Space Agency's (ESA) satellite. The objective of this study is to develop a new technique to improve the separation of protons and electrons, which are detected by the single-layer Timepix detector in SATRAM. The current identification method proposed by Gohl et al. (2019) is based on pattern recognition and stopping power measurements. In this article, the limitations of this method are discussed. A new method based on neural network trained with Geant4 data is proposed. Its validation with SATRAM data is presented. Similarly, a neural network trained with Geant4 data is introduced. Its purpose is to deduce the particles' incident energy using the energy deposited in the Timepix.

Timepix3: Temperature influence on X-ray measurements in counting mode with Si sensor

The Timepix3 radiation imaging and particle tracking detector is the direct successor to the Timepix semiconductor detector developed in CERN. The Timepix ASIC chip (256 × 256 pixels with a pitch of 55μm provides the possibility to operate each of the 65536 pixels in one of the following modes: (1) event counting (Medipix mode); (2) energy measurement (Time over Threshold — ToT mode); and (3) measurement of the interaction time (Time of Arrival — ToA mode). The Timepix3 chip of the new generation introduces the ability to measure ToT and ToA simultaneously and also the event-based readout where each hit pixel is read out immediately after the hit. This detector can be used in a variety fields of science including particle physics, X-ray imaging as well as medicine and space science. With regards to the wide application possibilities of this detector, we investigate the properties of the detector in the temperature range from −20°C to ＋80°C. This temperature range spans the majority of laboratory conditions as well as requirements for most of outer space missions. This paper describes thermal-vacuum testing of the most common 300µm Si detector with AdvaPIX readout interface in the counting mode. The detector was stabilised under various thermal conditions in a thermal vacuum chamber and subsequently exposed to characteristic X-ray radiation of 5 elements in the energy range of 4–24keV. It was found that the absolute measurement accuracy of higher energies is more affected by higher temperature (up to 0.8keV@17.48keV) and relative error of Timepix3 accuracy is inversely proportional to the incident X-ray energy. The relative precision is kept in the range of 6% for temperatures from −20°C to ＋60°C with significant change at ＋80°C.

Investigation of thick GaAs:Cr pixel sensors for X-ray imaging applications

The new generation of synchrotron radiation sources sets advanced requirements in the performance of hybrid pixel detectors. A critical point in the design of such detectors is the choice of the sensor material. Chromium-compensated Gallium Arsenide (GaAs:Cr) is a promising candidate for use in pixel detectors, targeting imaging applications in the intermediate energy range 20–50 keV. In this work, thick GaAs:Cr sensors grown recently using the Liquid Encapsulated Czochralski (LEC) method were bonded to Timepix chips. The performance of the sensors was characterised by using various X-ray sources in view of imaging applications. The uniform illumination of the sensors reveals inhomogeneities due to the presence of crystal defects in the microscopic level. Using a micro-focused X-ray beam we extract sensitivity maps and the mobility-lifetime product at the pixel level. The results obtained confirm that the non-uniformities observed at the sensor level are directly linked with the microscopic defects. Overall, the efficient use of such sensors in X-ray imaging applications relies on their stability over irradiation-time.

Study of charge sharing effect in a GaAs:Cr-based Timepix3 detector

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.

Registration of the transition radiation with GaAs detector: Data/MC comparison

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-angular distributions using a 500 |j.m thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed.

Thermal vacuum testing of Timepix3 detector

The thermal dependence of semiconductor detectors is one of their critical properties. This paper presents the results of the Timepix3 detector thermal vacuum testing, with respect to the effects on its properties and sensitivity. The Timepix3 represents a new generation of Timepix chips of the Medipix family, and it is equipped with an event-based mode of detection allowing for simultaneous measurement of the position, time and energy of an incident particle. Due to their properties, Timepix3 detectors are very suitable for space applications. Given that this is a relatively new device, the influence of temperature is not described in detail yet, especially for space usage. The operation of the device in a broad range of temperatures is required (e.q. QB50 mission on LEO from −20̂C to +50̂C). Timepix detectors have been used already in space missions, e.g. VZLUSAT-1, LUCID and SATRAM missions. In space, thermal cycling of the detectors occurs and this results in measurement distortion because both the noise edge and energy spectra are affected by changes in temperature. The experiments were performed on a detector equipped with a 300 μm thick Si sensor. The detector was equalised under various thermal conditions in vacuum and subsequently exposed to several energies of X-ray radiation corresponding to the characteristic radiation of 5 elements in the energy range of 4–24 keV. The results of these tests improve the knowledge regarding the behaviour of the essential components of the detector under extreme conditions. This new information can be used to improve measurements and thus minimise external influences, for example, in space applications but also in other fields where temperature stabilisation of the detector is very difficult or energy-consuming.

Studies of the spectral and angular distributions of transition radiation using a silicon pixel sensor on a Timepix3 chip

X-ray transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. In most of the detectors, emission of the X-ray transition radiation (TR) starts at Lorentz factors above γ∼500 and reaches saturation at γ∼2÷3⋅103. However, many experiments require particle identification up to γ∼105, which is very difficult to achieve with conventional detectors. Semiconductor pixel detectors offer a unique opportunity for precise simultaneous measurements of spectral and angular parameters of TR photons. Test beam studies of the energy and the angular distributions of TR photons emitted by electrons and muons of different momenta crossing several types of radiators were performed at the CERN SPS with a 480 μm thick silicon detector bonded to a Timepix3 chip. High resolution images of the energy−angle phase space of the TR produced by different radiators were obtained and compared with MC simulations. The characteristic interference patterns are in agreement with the theoretical models with an unprecedented level of details. The studies presented in this paper also show that simultaneous measurements of both the energy and the emission angles of the TR X-rays could be used to enhance the particle identification performances of TRDs.

Single-shot, omni-directional x-ray scattering imaging with a laboratory source and single-photon localization.

Omni-directional, ultra-small-angle x-ray scattering imaging provides a method to measure the orientation of micro-structures without having to resolve them. In this letter, we use single-photon localization with the Timepix3 chip to demonstrate, to the best of our knowledge, the first laboratory-based implementation of single-shot, omni-directional x-ray scattering imaging using the beam-tracking technique. The setup allows a fast and accurate retrieval of the scattering signal using a simple absorption mask. We suggest that our new approach may enable faster laboratory-based tensor tomography and could be used for energy-resolved x-ray scattering imaging.

Soft X-ray measurements with a gas detector coupled to microchips in laser-plasma experiments at VEGA-2

This work presents an innovative usage of the GEMpix detector for soft X-rays (SXR) measurements aimed to make an estimate of the electron temperature of a Laser Produced Plasma (LPP). The GEMpix is a proportional gas detector based on three Gas Electron Multipliers (GEMs) with a Front-End Electronics (FEE) based on four Timepix chips. This FEE provides the Time over Threshold (ToT) acquisition mode pixel by pixel and then a digital measure of the released charge in the gas mixture. In addition, the charge can be amplified through the GEM foils with 4 orders of magnitude spanning gain offering, in this way, a big dynamic range and adjustable sensitivity. Chip design provides a threshold for each channel. All the thresholds are set in order to cut electronic noise and detect X-rays. In this configuration, a cut on the low amplitude signals is set, but the gain has been tuned in order to observe the main signal due to the soft X-rays reaching the detector. This detector works in an energy range between 2 to 15 keV . It offers good imaging properties, high efficiency and absolute calibration. It offers a good immunity to Electromagnetic Pulse (EMP), as checked at VEGA-2 laser facility (hundreds of TW in about 30 fs). In these experiments, where the formation of warm dense matter produced by blast waves has been studied, a measure of the plasma temperature was required. This measurement was realized applying some filters on the active area of the detector, in correspondence of three chips. With this configuration a study of the GEMpix response due to the photons coming from the coronal plasma produced by the laser on the target has been done for each single shot. GEMpix revealed innovative and attractive features, compared to the state of the art where passive films or detectors based on indirect conversion are used, for SXR imaging and spectral analysis to infer the electron temperature.

Improving spatial resolution by predicting the initial position of charge-sharing effect in photon-counting detectors

X-ray photon-counting detectors are considered as next generation x-ray detectors because they offer several advantages over conventional energy-integrating detectors, such as the ability to obtain energy information due to the photon-counting capability. In addition, the contrast-to-noise ratio in a photon-counting detector is higher than that of a conventional charge-integration detector due to its direct detection of radiation. Nevertheless, it suffers from charge sharing effect which is caused by diffusion of electrons generated from incident x-rays and k-edge escape photon to other pixels. Due to these phenomena, distortion can occur in terms of the position information and the energy information. In this work, we used the time-over-threshold (ToT) and projection method to compensate for charge sharing. We projected the charge-sharing value of eight neighboring pixels to the center pixel and found the point where the photon had the highest probability of entering the center pixel. We then divided the center pixel into 3 × 3 sections and found the location where the very first x-ray photon was incident through the projection. Using a timepix chip with CdTe pixels, 50,000 images were acquired for 1.5 seconds at intervals of 30 us with the ToT method. At this time, x-ray irradiation was applied to various materials at 80 kVp and 5 uA.

Performance of the GridPix detector quad

A gaseous pixel readout module with four GridPix chips, called the quad, has been developed as a building block for a large time projection chamber readout plane. The quad module has dimensions 39.6mm×28.38mm and an active surface coverage of 68.9%. The GridPix chip consists of a Timepix3 chip with integrated amplification grid and have a high efficiency to detect single ionization electrons, which enable to make a precise track position measurement. A quad module was installed in a small time projection chamber and measurements of 2.5GeV electrons were performed at the ELSA accelerator in Bonn, where a silicon telescope was used to provide a reference track. The error on the track position measurement, both in the pixel plane and drift direction, is dominated by diffusion. The quad was designed to have minimum electrical field inhomogeneities and distortions, achieving systematics of better than 13µm in the pixel plane. The resolution of the setup is 41µm, where the total systematic error of the quad detector is 24µm.

First tests with Timepix2 and heavy ions

We investigate the response of the new Timepix2 chip to heavy ions. Understanding this response is important to understand the performance and capabilities of this chip in the space environment, where it is a possible replacement for the existing Timepix chip which is already widely used in space. We carry out measurements on Timepix2 using a variety of heavy ion beams. We find that the Timepix2 generally performs as expected for a variety of measurements. We confirm that the Timepix2 front end can measure up to at least 2.2MeV in silicon per pixel. We also confirm that improvements in the pixel interaction with the shutter allow for measurements of individual tracks in fields substantially more intense than those measurable by Timepix. We conclude that the Timepix2 is a very promising candidate for use in space radiation measurements.

Timepix3 detector and Geant4-based simulations for gamma energy detection in Laser Produced Plasmas

The particular physics of Laser Produced Plasmas (LPP) needs some diagnostic requirements. Specifically, the X-ray monitoring of the plasma is known to be difficult since typically X-ray emissions are concentrated in bursts from a few tens of ps to few ns, based on the power and pulse time width of the laser. Therefore, the energy measurement of the radiation coming from a single experimental run is basically unfeasible using conventional techniques. Additional particles can be produced from LPP experiments, especially high energy gamma photons and electrons. As a case study in recent experiments, carried out on VEGA-2 laser facility (CLPU, Salamanca, Spain), the aim was to produce neutrons through photonuclear reactions on different types of solid targets. We have used the Timepix3 chip, in a “side-on” configuration, in order to produce a quick estimate of the gamma photons energy involved in the reactions. This detector, based on silicon, is realized with a single chip of 256 × 256 pixels bump-bonded with a 14 mm × 14 mm × 300 μm silicon layer. Interaction of gammas with the detector in this configuration produces some characteristic clusters of pixels and, for each cluster, a variety of physical and morphological parameters can be defined. Based on some of these parameters, we have characterized the detector response using some known laboratory gamma sources and the related Geant4 simulations. This allows quick energy discrimination for the gamma photons coming from different experimental runs.

Development of the GridPix detector quad

We have developed the gaseous GridPix detector quad made from four Timepix3 chips. To provide the required charge amplification a Micromegas-like grid has been deposited on the chip surface by MEMS technology. The grid holes are precisely aligned to the chip pixels and have a pitch of 55 μm while the high time resolution of 1.56 ns of the Timepix3 chip enables the precise reconstruction of each individual primary ionization electron in the detector gas. The chip is coated by a high resistivity protection layer to prevent damage by unavoidable discharges. Using the GridPix technology, the full position of the ionization cloud is measured. As such the ultimate resolution of a gaseous detector is achieved, mainly limited by diffusion. The quad has all services located under the detection surface. Multiple quads can be simply joined together to create a large readout plane of a TPC. In this paper we show details about the construction of the quad and the preliminary results from a recent test beam experiment at the ELSA electron beam facility in Bonn.

Timewalk correction for the Timepix3 chip obtained with real particle data

In this work we have developed a prototype gaseous pixel detector by combining a micromegas grid with a Timepix3 chip for the readout. The micromegas foil supported by a matrix of pillars about 50 $\mathrm{\mu m}$ high was manually placed on top the chip. By placing a cathode foil above the chip an ionization detector was created with a drift gap of 13.5 mm. The Timepix3 chip, thanks to the simultaneous measurement of the time-of-arrival (ToA) and charge via time-over-threshold (ToT) allows corrections to remaining timewalk effects, improving further the position resolution along the drift direction. We present the timewalk correction for Timepix3 chip obtained with real data from a particle beam and its impact on the tracking performance. The results obtained show an significant improvement on the position resolution for single-hits and tracks along the drift direction compared to previous experiments.

Transition radiation measurements with a Si and a GaAs pixel sensor on a Timepix3 chip

Growing energies of particles at modern or planned particle accelerator experiments as well as cosmic ray experiments require particle identification at gamma-factors (γ) of up to ∼105. At present there are no detectors capable of identifying charged particles with reliable efficiency in this range of γ. New developments in high granular pixel detectors allow one to perform simultaneous measurements of the energies and the emission angles of generated transition radiation (TR) X-rays and use the maximum available information to identify particles. First results of studies of TR energy-angular distributions using gallium arsenide (GaAs) sensors bonded to Timepix3 chips are presented. The results are compared with those obtained using a silicon (Si) sensor of the same thickness of 500 μm. The analysis techniques used for these experiments are discussed.