197,496 research outputs found
Computer simulation of the electronic noise of solid-state detectors
No full textIn this paper we propose a mathematical procedure to computer simulate the electronic noise of ionizing-radiation spectrometers as observed at the output of the preamplifier or of the anti-aliasing filter, just in front of the ADC. Examples are given for the case of segmented HPGe (High Purity Germanium) detectors. The method makes use of the fractional calculus basics. A software procedure provides the noisy waveform as a function of the fundamental electrical-physical parameters of the system, including: detector capacitance, detector leakage current, feedback resistor, 1/f-noise coefficient of the input transistor, temperature of the preamplifier input devices
Spectroscopic technique for optimal P-Z setting in gamma-ray detection
No full textA spectroscopic technique for optimally setting the Pole-Zero (P-Z) compensation in a digital spectrometer has been implemented, which has substantially improved the resolution of the measurements at high count rates. Before ADC conversion the signal undergoes an analog preprocessing, consisting of Pole-Zero compensation and simple three-pole shaping, which is the proper antialiasing-filter shape in this context. A subsequent suitable digital filter optimizes the overall weight function and introduces digital baseline restoration. It is well known that an imperfect P-Z setting causes pulse-tail pileup which is seen as an additional noise and may impact significantly on the final resolution of the measurements, particularly at high count rates. We introduce a spectroscopic technique which permits a second-order tuning of the P-Z compensation. Such a fine-tuning degree, which definitely could not be attained by oscilloscope observation, yields a substantial improvement in the performance of the system. Namely, at a count rate of 20kcounts/s the second-order tuning (1% adjustment) yields a 30% narrowing of the width of the 1.33MeV 60Co line
VLSI cryogenic front-end for HPGe detectors based on a silicon-germanium technology
No full textWe studied the feasibility of monolithic silicon-germanium front-ends for cryogenic semiconductor detectors. In this framework we designed and simulated a low-noise Charge Sensitive Preamplifier for High Purity Germanium detectors using the Austria Micro System S35 silicon-germanium technology. The preamplifier uses two silicon-germanium Hetero-junction Bipolar Transistors, a few silicon Metal-Oxide-Silicon Field-Effect Transistors, and an external silicon Junction Field-Effect Transistor. It is designed for gamma-ray spectroscopy performance at liquid-argon temperature, and exploits the full functionality at cryogenic temperatures of silicon-germanium Bipolar Transistors. Single-channel and four-channel versions are being realized
Measurement requirements and front-end design rules for gamma-ray tracking in large-volume germanium detectors through pulse-shape analysis
No full textIn this paper we address the design of a mixed analogue-digital processor for pulse-shape analysis of signals delivered by large volume High-Purity-Germanium (HPGe) detectors for gamma-ray spectroscopy. The information to be extracted from pulse-shape analysis is the position of the interaction of the gamma photon inside the detector. We discuss the structure of the measurement apparatus and the required characteristics of its components, with a special emphasis on the resolution and sampling frequency of the analogue-to-digital converter (ADC). We also address the problem of the occurrence time estimate of the events, which is strictly related to the pulse shape. A modular hardware solution for pulse-shape measurements is proposed
Optical charcaterization of industrial slurries
No full textIn this work we focus at the characterization of micro- and nano-powders typically adopted for chemical mechanical polishing, extensively exploited whenever global and local planarization of surfaces is required as in nanoelectronic fabs. We present an innovative method for accurate characterization of water suspensions of nanoparticles. It relies upon the combination of a new approach to extract light scattering information from single particles and the recently developed diagnostic tool named Single Particle Extinction and Scattering. It can be exploited in line. Data interpretation becomes independent of any a priori assumption about the samples. The results of accurate measurements performed on Ceria as well as Aluminum oxide surries are reported. We show strong advantages of this method with respect to traditional ones by explicitly reporting experimental results on calibrated spheres made of different materials. We discuss possible applications for in line characterization of ultrapure water, chemicals, slurries for abrasive processes, for example, as well as the detection of any undesired particles could be the key for future improvements of advanced process control systems
Extending the dynamic range of a charge-preamplifier far beyond its saturation limit : a 0.35 μm CMOS preamplifier for germanium detectors
No full textThe dynamic range of integrated charge-sensitive preamplifiers for germanium detectors is typically limited to ~5 MeV, owing to the intrinsically low available voltage swing of scaled CMOS technologies and to the very high sensitivity needed to achieve energy resolutions of ~0.1% @ 2 MeV. We propose a circuit technique that allows for high-resolution energy measurements, compatible with gamma-spectroscopy standards, also in the case of large input signals yielding a deep saturation of the charge preamplifier. The preamplifier has been designed and simulated in a 5V 0.35 μ m CMOS technology. The idea relies on the fact that the physical information, i.e. the charge released by the germanium crystal, is not destroyed by the saturation of the charge sensing stage. The exceeding charge, that cannot be stored on the feedback capacitance, is temporarily stored on the other capacitances connected at the input node, namely the detector capacitance and the input JFET capacitance. The CMOS circuit comprises a fast-reset device connected at the input node of the circuit and performing the fast de-saturation of the charge sensing stage. A first-order linear relation exists between the input charge and the reset time. By estimating the input charge through the direct measure of the reset time, a substantial increase of the energy measurement range is achieved
How to optimize VLSI ROTOR processors
No full textThe principle of operation of ROTOR, a novel processor of nuclear signals, has been recently demonstrated. Nevertheless the prototype versions realised so far are affected by limiting fetors which do not permit to fully exploit the potentiality of the ROTOR principle. For example presently the shape of the filter weight function is forced to be trapezoidal, which is not notimal for low-rate operation and/or when the 1/f noise of the preamplifier is not negligible. Furthermore a very precise timing must be supplied for proper operation. In this paper we suggest that these limitations can be overcome by (i) shrinking the analog pulses provided by the preamplifier, (ii) supplying them to the reference input of a DAC used as a multiplier, whose digital-input tracks the wanted weight function shape, (iii) integrating the signal at the DAC output. In this way on the one hand the weight function may be shaped so as to match the optmal profile, on the other hand precision is no more required in the gating intervals where the flat top and the shoulders of the weight function lay. Eventually the proposed solution is shown to be less sensitive to the parameter-matching accuratness of the used technology
A compact back-end module for high-rate multielement X-ray spectrometers and γ-ray imagers
No full textA compact single-ADC back-end module for the derandomization, acquisition and memorization of 16 spectra from high-rate multielement radiation detectors has been designed and characterized. The input signals, as provided by external peak stretchers, feed Sample&Hold circuits operated independently, which makes it possible to capture randomly-occurring events even in the worst case of time coincidences in different detection elements. The stored signals are then passed along synchronously to a common 12-bit 10MHz flash ADC, by means of a switch array operated as a multiplexer. This provides derandomization of the arrival times of the events. A maximum count rate of about 500 kcounts/s/channel is featured. An homogeneous processing rate among the channels is guaranteed by driving the switches with an "intelligent" digital circuitry implemented in two programmable-logic units. Sliding-scale correction is used to reduce by two order of magnitudes the ADC native differential nonlinearity, and so to meet the requirements of the spectroscopic applications. The measured pulser-peak noise is 1.5 bins r.m.s. over a full scale of ∼4000 bins
Ion spectroscopy : a diamond characterization tool
No full textThe stopping power Delta E and the energy-loss resolution delta E/Delta E of Single-Crystal CVD-Diamond Detectors (SC-DDs) measured with relativistic Heavy Ions (HIs) are interpreted as global quality parameters, characterizing simultaneously crystal texture and carrier-trapping concentrations, as well as the charge-transport properties of intrinsic diamond samples. HI spectra are presented, where spectral lines are obtained similar to the predictions of the Lindhard and Sorensen (LS) theory [J. Lindhard, A.H. Sorensen, Phys. Rev. A 53 (1996) 2443]. The spectroscopic results indicate an almost defect free material, and spatial homogeneity of all parameters relevant to the detector signal (i.e., mass density, dielectric constant, drift mobility and velocity of the charge carriers). Measured and simulated transient current signals generated by relativistic Xe-132 ions are discussed according to theories [A. Many, G. Rakavy, Phys. Rev., 126 (1962) 1980: G. Juska, M. Viliunas. O. Klima, E. Sipek. J. Kocka, Phil, Mag. B 69 (1994) 277; G. Juska, M. Viliunas, K. Arlauskas, J. Kocka, Phys. Rev. B 51 (1994) 16 668] of space-charge limited current (SCLC) transients. The evidence of the spectroscopic results is confirmed by the current-mode studies, and thus indirectly, the potential of the characterization method as well
Single-transistor option for high-resolution gamma-ray spectroscopy in hostile environments
No full textWe designed and realized a low-noise charge preamplifier for HPGe (High Purity Germanium) gamma-ray detectors, able to operate at a distance of 3 to 6 m from the detector. One transistor only is placed in close proximity to the detector. Such a setup is required in applications where the detector works in hostile environments that could damage or destroy the electronic circuitry. Using 3 m RG62 cables and a 23 pF detector capacitance we obtained a noise of ~1.07 keV fwhm at 2 μs shaping time, so fully compatible with gamma-spectroscopy requirements. By compensating the preamplifier so as to completely eliminate the ringings in its response function we obtained a rise-time of ~46ns with 3 m cables and of ~80ns with 5 m cables. With a different approach, or using a lower compensation capacitance and eliminating the ringings through a numerical post filter, we obtained a faster rise time of ~33 ns, with a detector-preamplifier distance of 5 m, while maintaining the low-noise performance. This latter setup is adequate for spectroscopy and tracking of gamma rays with segmented HPGe detectors
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