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Currently, we are developing a neutron scintillation detector prototype using silicon photomultipliers (SiPMs) as the photodetector. In order to reconstruct the position of single neutron events to an accuracy better than the pixel pitch of the SiPM, a very accurate photon count is required. Each pixel consists of 3200 microcells, operated in Geiger mode. A cell which is already triggered cannot detect any following photons hitting the cell, until it is recharged. This leads to a nonlinearity in the pixel’s response for a higher photon density impinging across the pixel. Previous studies provided a correction factor to estimate the saturation, by assuming a homogeneous photon distribution density and comparing it to the number of microcells. In our specific application, the photon distribution is not homogeneous, which is why we examined the influence of the homogeneity on the saturation. In this work, we present a case study for difference in nonlinearity effect for an inhomogeneous and homogeneous photon distribution density, given the light intensity is equal. The simulation results suggest that the effect could be higher for an inhomogeneous distribution. Therefore, care must be taken when using the established correction factor for saturation and an analysis of the photon distribution homogeneity is necessary. [ABSTRACT FROM AUTHOR]

We obtain experimental chimera states in the minimal network of three identical mechanical oscillators (metronomes), by introducing phase-lagged all-to-all coupling. For this, we have developed a real-time model-in-the-loop coupling mechanism that allows for flexible and online change of coupling topology, strength and phase-lag. The chimera states manifest themselves as a mismatch of average frequency between two synchronous and one desynchronized oscillator. We find this kind of striking "chimeric" behavior is robust in a wide parameter region. At other parameters, however, chimera state can lose stability and the system behavior manifests itself as a heteroclinic switching between three saddle-type chimeras. Our experimental observations are in a qualitative agreement with the model simulation. [ABSTRACT FROM AUTHOR]

In recent years, the price increase of 3He has triggered the search for alternative neutron detectors. One of the viable options is a scintillation-based neutron detector. Usually, photomultiplier tubes (PMTs) are used in these detectors for photodetection. However, the increase in performance requirements such as the operability in magnetic field and spatial resolution necessitates an advanced neutron detector. Therefore, we developed a detector prototype with an active area of 13 cm × 13 cm using silicon photomultipliers (SiPMs). As compared to PMTs, SiPMs offer more compactness, more robustness, and a lower sensitivity to magnetic field. The final detector is aimed to be used in the future at the TREFF instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany, for neutron reflectometry (NR). First measurements were carried out at TREFF and at the dedicated detector test instrument V17 at BER-II of HZB in Berlin, Germany. In this study, we report the results for detection efficiency, gamma discrimination, 2-D position resolution, count rate, and detection linearity. [ABSTRACT FROM AUTHOR]

The energy consumed by electron devices such as field-effect-transistors (FET) in an integrated circuit is mostly used to process different electrical signals. However, a fraction of that energy is also converted into heat that gets transferred throughout the integrated circuit and modifies the local temperature. The modification of the local temperature, which is interpreted as a self-heating mechanism, is a function of different charge carrier scattering mechanisms, the characteristic energy relaxation times for charge carriers, the heat carrier mechanisms, the geometry of the FET, the volume of the integrated circuit, and the composed thermal properties of the integrated circuit and the system package. Besides all those dependencies, the charge and heat transport properties are temperature dependent. All these features make the electrothermodynamic analysis and modeling of low-power cryogenic electron devices a compulsory need. In this work, we introduce an analysis based on experimental results obtained from characterizing FET test structures in the temperature range between 300 K and down to 3.1 K. [ABSTRACT FROM AUTHOR]

Electrical impedance tomography (EIT) is gaining importance in the field of geophysics and there is increasing interest for accurate borehole EIT measurements in a broad frequency range (mHz to kHz) in order to study subsurface properties. To characterize weakly polarizable soils and sediments with EIT, high phase accuracy is required. Typically, long electrode cables are used for borehole measurements. However, this may lead to undesired electromagnetic coupling effects associated with the inductive coupling between the double wire pairs for current injection and potential measurement and the capacitive coupling between the electrically conductive shield of the cable and the electrically conductive environment surrounding the electrode cables. Depending on the electrical properties of the subsurface and the measured transfer impedances, both coupling effects can cause large phase errors that have typically limited the frequency bandwidth of field EIT measurements to the mHz to Hz range. The aim of this paper is to develop numerical corrections for these phase errors. To this end, the inductive coupling effect was modeled using electronic circuit models, and the capacitive coupling effect was modeled by integrating discrete capacitances in the electrical forward model describing the EIT measurement process. The correction methods were successfully verified with measurements under controlled conditions in a water-filled rain barrel, where a high phase accuracy of 0.8 mrad in the frequency range up to 10 kHz was achieved. The corrections were also applied to field EIT measurements made using a 25 m long EIT borehole chain with eight electrodes and an electrode separation of 1 m. The results of a 1D inversion of these measurements showed that the correction methods increased the measurement accuracy considerably. It was concluded that the proposed correction methods enlarge the bandwidth of the field EIT measurement system, and that accurate EIT measurements can now be made in the mHz to kHz frequency range. This increased accuracy in the kHz range will allow a more accurate field characterization of the complex electrical conductivity of soils and sediments, which may lead to the improved estimation of saturated hydraulic conductivity from electrical properties. Although the correction methods have been developed for a custom-made EIT system, they also have potential to improve the phase accuracy of EIT measurements made with commercial systems relying on multicore cables. [ABSTRACT FROM AUTHOR]

Currently both preclinical and clinical PET systems are built with pixilated, optically isolated scintillators. The use of optical isolators limits the achievable packing fraction for designs that use small crystals. No optical isolation is necessary in a monolithic scintillation crystal design hence the sensitivity is increased. The light distribution created by a high energy interaction in a monolithic scintillator can be readout by a SiPM-array to determine the 3-D position of the interaction. We have developed a digital pulse width modulation readout circuit that is able to readout many densely packed SiPM-arrays connected to monolithic scintillators. A monolithic scintillation detector requires simultaneous acquisition of the light distribution on multiple sensors unlike in a one-to-one optically isolated pixelated configuration. Therefore, pulse width modulation can reduce the readout complexity of the monolithic scintillation detector. The circuit gives an output signal with a pulse width linear to the incoming charge. Therefore, the circuit provides both timing and intensity information using just one digital line per channel. The charge to pulse-width conversion ratio of the circuit is adjustable (e.g., 33 ns/pC). The trigger jitters \sigma 41.2 ps between two channels. The PCB offers 8 channels and comes with additional features: The gain variation of a SiPM is compensated over a large temperature range by controlling the bias voltage. We measured from 15^\circC to 42^\circC, here it can bring the variation of a SiPM in gain from -21 ns/^\circC to +3.8 ns/^\circC or stabilizes the variation of the energy resolution between 18 and 20%. [ABSTRACT FROM PUBLISHER]

A photoreceiver optoelectronic integrated circuit based on InP with a bandwidth of 37 GHz is presented. The receiver consists of a 50 GHz waveguide-integrated photodiode and a distributed amplifier with a bandwidth of 39.5 GHz, which is composed of four high-electron mobility transistors. A system experiment at 40 Gb/s receiving an return-to-zero coded optical input signal is demonstrated, and a good quality of eye pattern is achieved [ABSTRACT FROM PUBLISHER]