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We report on the design of an active feedback circuit for charge sensitive amplifiers used for reading out hybrid pixel detectors. The predominant advantages of the proposed feedback over the existing solutions are its low noise, stability, and tunability. In addition, the circuit occupies small silicon area, which is crucial for hybrid pixel detectors. This paper presents both the mathematical analysis of the proposed circuit and measurement results obtained with the test structure.

Spectrally selective X-ray imaging provides improved material and tissue discrimination in comparison with the state-of-the-art dual energy technologies that are commonly used in medical, industrial, and security applications. Cadmium telluride (CdTe)- and cadmium zinc telluride (CdZnTe)-based line scanners and small size two-dimensional X-ray sensors are emerging to the market, but the need for large-scale panels is axiomatic. In this study, a seamless CdTe tile was developed that enables the implementation of large-sized, energy selective X-ray detector panels. The developed tile consists of a $64\times64$ pixel array (with $150~\mu \text{m}$ pitch) with a necessary substrate, ASIC, and CdTe crystal. The performance of the constructed seamless tile was characterized by focusing on spectral resolution and stability. In addition, a simple pixel trimming method that automates the equalization of each energy selective pixel was developed and analyzed. The obtained results suggest that the proposed concept of seamless (tileable) detector structures is a feasible approach to scale up panel sizes. The seamless tile shows comparable spectral resolution and stability performance with commercial CdTe sensors. The effect of tile to tile variation, the realization of a large-scale panel, as well as the charge sharing performance were left out of the scope and are to be studied in the next phase.

An on-chip implementable algorithm for allocation of an X-ray photon imprint, called a hit, to a single pixel in the presence of charge sharing in a highly segmented pixel detector is described. Its proof-of-principle implementation is also given supported by the results of tests using a highly collimated X-ray photon beam from a synchrotron source. The algorithm handles asynchronous arrivals of X-ray photons. Activation of groups of pixels, comparisons of peak amplitudes of pulses within an active neighborhood and finally latching of the results of these comparisons constitute the three procedural steps of the algorithm. A grouping of pixels to one virtual pixel , that recovers composite signals and event driven strobes, to control comparisons of fractional signals between neighboring pixels are the actuators of the algorithm. The circuitry necessary to implement the algorithm requires an extensive inter-pixel connection grid of analog and digital signals, that are exchanged between pixels. A test-circuit implementation of the algorithm was achieved with a small array of $32\times 32$ pixels and the device was exposed to an 8 keV highly collimated to a diameter of 3- $\mu \text{m}$ X-ray beam. The results of these tests are given in this paper assessing physical implementation of the algorithm.

Nowadays, single photon counting pixel hybrid detectors are becoming increasingly popular in high-energy physics, X-ray detectors for synchrotron applications, and medical imaging. Readout chips for these detectors usually have the area of a few square centimeters and are designed to be abutted on three sides. However, many applications require large-area detectors without dead areas. The through-silicon vias (TSVs) aim to minimize the dead area and in that way to enable development of four-side buttable large-area detectors. AGH, Krakow, and IZM, Berlin, have undertaken a common effort to apply TSV (via last) technology to the readout integrated circuit called UFXC32k containing a matrix of $128 \times 256$ pixels, with a pixel pitch of $75~\mu \text{m}$ and a total area of 2 cm2. The TSVs were applied to the 87 I/O pads located at the bottom of UFXC32k IC. A TSV diameter of $20~\mu \text{m}$ was chosen while the wafers were thinned to $100~\mu \text{m}$ . The redistribution layer and the array of pads for solder bumping were distributed at the bottom side of the chips. Two UFXC32k chips with TSVs were attached to a single, 320- $\mu \text{m}$ -thick silicon sensor and finally, the chip detector modules were attached to low-temperature co-fired ceramic boards. The $2 \times 2$ cm2 plug-in detector modules were successfully built and tested.

A combined X-ray photon correlation spectroscopy and rheology study is carried out to capture the evolution of structure, fast particle-scale dynamics, and moduli (elastic and loss) at early times of gel formation near the fluid–gel boundary of a suspension of nanoparticles. The system is comprised of moderately concentrated suspensions of octadecyl silica in decalin (ϕ = 0.2) undergoing thermoreversible gelation. Near the gel boundary, the rate of gel formation is very sensitive to changes in attraction strength. However, we find that at different attraction strengths, the system goes through identical intermediate states of microscopic and macroscopic behavior, even though the absolute time needed to form a gel varies by orders of magnitude. We identify a single dimensionless time parameter, tw/tg, where tw is the wait time following the quench and tg is the rheologically determined gel time, that captures the similarity in gel formation at a range of attraction strengths. Following a temperature quench below the gel boundary, the system is initially fluidlike and forms diffusive clusters (∼8.5 times the particle diameter). After a lag-time, tL, clusters aggregate to form a network like structure which is characterized by the onset of mechanical rigidity and a rapid growth in microscopic relaxation times. At tg, the Baxter parameter obtained from adhesive hard sphere fits of the structure factor attains a constant value corresponding to the theoretical percolation boundary, thus demonstrating that gelation is percolation driven.

X-ray photon correlation spectroscopy is performed using a dual counter pixel array detector at a frame rate of 11.8 kHz with no readout dead-time., Small-angle scattering X-ray photon correlation spectroscopy (XPCS) studies were performed using a novel photon-counting pixel array detector with dual counters for each pixel. Each counter can be read out independently from the other to ensure there is no readout dead-time between the neighboring frames. A maximum frame rate of 11.8 kHz was achieved. Results on test samples show good agreement with simple diffusion. The potential of extending the time resolution of XPCS beyond the limit set by the detector frame rate using dual counters is also discussed.

This paper presents a readout integrated circuit called UFXC32k, designed for hybrid pixel semiconductor detectors used in X-ray imaging applications. The UFXC32k integrated circuit, designed in a CMOS 130 nm process, contains about 50 million transistors in the area of $9.64\;\hbox{mm} \times 20.15\;\hbox{mm}$ . The core of the IC is a matrix of $128 \times 256$ square-shaped pixels of ${\hbox{75}}\;\mu\hbox{m}$ pitch. Each pixel contains a charge sensitive amplifier, a shaper, two discriminators, and two 14-bit ripple counters. The analog front-end electronics allow processing of sensor signals of both polarities (holes and electrons). The UFXC32k chip is bump-bonded to a pixel silicon sensor and is fully characterized using X-ray radiation. The measured equivalent noise charge for the standard settings is equal to $123\ {{\rm e}^ - }\;\hbox{rms}$ (for the peaking time of 40 ns) and each pixel dissipates $26\;\mu\hbox{W}$ . Thanks to the use of trim blocks working in each pixel independently, an effective offset spread calculated to the input is only $9\ {{\rm e}^ - }\;\hbox{rms}$ with a gain spread of 2%. The maximum count rate per pixel depends mainly on effective CSA feedback resistance. Dead time in the front end can be set as low as 85 ns. In the continuous readout mode, a user can select the number of bits read out from each pixel to optimize the UFXC32k frame rate, e.g., for a readout of 2 bits/pixel with 200 MHz clock, the frame rate is equal to 23 kHz.

We report on a novel technique of an in-pixel multilevel offset correction to be used in hybrid pixel detector readout circuits operating in a single photon counting mode. This technique was implemented in a prototype integrated circuit consisting of 23,552 square shaped pixels of $75\ \mu \hbox{m}$ pitch, which was designed and manufactured in CMOS 130 nm technology. Each pixel contains a charge sensitive amplifier, shaper, two discriminators, two 14-bit counters and a block for multilevel offset correction. The effective gain and offset are controlled individually in each pixel. The measurement results prove very good uniformity of the prototype integrated circuit with an offset spread of only 7 ${{\rm e}^ - }{\rm rms}$ and a gain spread of 2.5%.

The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids.

The paper presents a prototype integrated circuit built in a 40 nm CMOS process for readout of a hybrid pixel detector. The core of the IC constitutes a matrix of $18 \times 24$ pixels with the pixel size of $100~\mu\hbox{m} \times 100~\mu\hbox{m}$ . The paper explains the functionality and the architecture of the IC, which is designed to operate in both the standard single photon counting mode and the single photon counting mode with interpixel communication to mitigate negative effects of charge sharing. This article focuses on the measurement results of the IC operating in the standard single photon counting mode. The measured ENC is $84{\rm e}^{-}~\hbox{rms}$ (for the peaking time of 48 ns), the gain is $79.7~\mu\hbox{V}/{\rm e}^{-}$ , while the effective threshold dispersion is $21{\rm e}^{-}~\hbox{rms}$ .

The VIPIC1 readout integrated circuit was designed for X-ray Photon Correlation Spectroscopy experiments that are typically performed using mono-energetic (8 keV) X-rays at a synchrotron radiation facility. The device is a pixel detector with sparsification and parallel readout from the groups, yielding high timing resolution. Recent improvements in bonding alignment of wafers resulted in deliveries of 3D bonded wafers. The stacks, bonded with both the Cu-Cu thermo-compression method and the Cu DBI bonding method, yielded operational devices that have been tested. Chips (with a pixel pitch of $80~\mu\hbox{m}$ ) were also bonded to silicon pixelated sensors (with a pixel pitch of $100~\mu\hbox{m}$ ) and the assemblies were exposed to X-ray sources for the first time. The paper focuses on the test results, including the calibrated noise (ENC) and the conversion gain. The noise measured corresponded to $39~\hbox{e}^ {- }$ and $70~\hbox{e}^ {- }$ , respectively for the readout channels that were not connected and connected to the sensor diodes. The conversion gain varied from 43 to $52~\mu\hbox{V/e}^ {- }$ as a function of the bias current in the front-end block. Essentially all the pixels on a small prototype were operational.

We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, T_{gel}, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT=T_{quench}-T_{gel}), wave vector, and formation time t_{f}. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular ΔT and t_{f} map to those at other ΔTs and t_{f}s via an effective scaling temperature, T_{s}. A single T_{s} applies to a broad range of ΔT and t_{f} but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures.

International audience; Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 ( $\sqrt{s_{NN}}=$ 2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials ( $\mu_B > 500$ MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter.

In this paper we present a measurement system for in vivo multichannel recordings of the electrophysiological activity of brain tissue. The system consists of penetrating Microelectrode Array (MEA), three versions of a Conditioning Module each equipped with different Application Specific Integrated Circuits (ASIC), Digitizer and PC Application for recorded data presentation and storage. The MEA consists of 64 15 μm diameter microelectrodes. The multichannel ASICs amplify and filter field and action potential signals. The custom-made Digitizer Module simultaneously acquires data from all channels with a 14 kS/s sample rate and 12 bit resolution. The resulting byte stream (about 2 MB/s) is transmitted to the PC via USB (Universal Serial Bus). Eventually the measurement data is decoded, presented to the system user and stored on a HDD. Preliminary system tests confirm its excellent performance (low input refereed noise, low power consumption, low area occupancy, ability of Action Potentials/Local Field Potentials separation). Our system equipped with multichannel ASICs meets requirements of many different neurobiology experiments.