Highest time resolution in scintillator based detectors is becoming more and more important. In medical detector physics L(Y)SO scintillators are commonly used for time of flight positron emission ...tomography (TOF-PET). Coincidence time resolutions (CTRs) smaller than 100ps FWHM are desirable in order to improve the image signal to noise ratio and thus give benefit to the patient by shorter scanning times. Also in high energy physics there is the demand to improve the timing capabilities of calorimeters down to 10ps. To achieve these goals it is important to study the whole chain, i.e. the high energy particle interaction in the crystal, the scintillation process itself, the scintillation light transfer in the crystal, the photodetector and the electronics. Time resolution measurements for a PET like system are performed with the time-over-threshold method in a coincidence setup utilizing the ultra-fast amplifier-discriminator NINO. With 2×2×3mm3 LSO:Ce codoped 0.4%Ca crystals coupled to commercially available SiPMs (Hamamatsu S10931-050P MPPC) we achieve a CTR of 108±5ps FWHM at an energy of 511keV. Under the same experimental conditions an increase in crystal length to 5mm deteriorates the CTR to 123±7ps FWHM, 10mm to 143±7ps FWHM and 20mm to 176±7ps FWHM. This degradation in CTR is caused by the light transfer efficiency (LTE) and light transfer time spread (LTTS) in the crystal. To quantitatively understand the measured values, we developed a Monte Carlo simulation tool in MATLAB incorporating the timing properties of the photodetector and electronics, the scintillation properties of the crystal and the light transfer within the crystal simulated by SLITRANI. In this work, we show that the predictions of the simulation are in good agreement with the experimental data. We conclude that for longer crystals the deterioration in CTR is mainly caused by the LTE, i.e. the ratio of photons reaching the photodetector to the total amount of photons generated by the scintillation whereas the LTTS influence is partly offset by the gamma absorption in the crystal.
For the full exploitation of the excellent timing properties of the Multigap Resistive Plate Chamber (MRPC), front-end electronics with special characteristics are needed. These are (a) differential ...input, to profit from the differential signal from the MRPC (b) a fast amplifier with less than 1ns peaking time and (c) input charge measurement by Time-Over-Threshold for slewing correction. An 8-channel amplifier and discriminator chip has been developed to match these requirements. This is the NINO ASIC, fabricated with 0.25μm CMOS technology. The power requirement at 40mW/channel is low. Results on the performance of the MRPCs using the NINO ASIC are presented. Typical time resolution σ of the MRPC system is in the 50ps range, with an efficiency of 99.9%.
TDCpix pixel detector ASIC with 100 ps time stamping Rinella, G. Aglieri; Bonacini, S.; Jarron, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2023, Volume:
1053
Journal Article
Peer reviewed
Open access
The TDCpix pixel read-out ASIC contains 1800 pixels arranged in 40 columns and 45 rows with the dimension of 300μm x 300μm. Each pixel contains a preamplifier and shaper circuit with a dynamic range ...of 0.8 to 10 fC and a rise time of 5 ns, followed by a Leading-Edge discriminator with Time-over-Threshold correction. The discriminator outputs of each pixel are connected to time-to-digital converters (TDC) measuring the time when the input signal has exceeded the threshold and the pulse width with a binning of 97 ps. The electronics noise of pre-amplifier/shaper is 170 e− or 2.7 mV rms with a gain of 65 mV/fC. The jitter of the entire processing chain for an electrical input signal of 2.4 fC is lower than 60 ps rms. The ASIC has been designed to work in radiated environments of 6 * 104 Gray per year and 2 x 1014 1 MeV neutron equivalent cm−2.
The renewal of interest in Time of Flight Positron Emission Tomography (TOF-PET), as well as the necessity to precisely tag events in high energy physics (HEP) experiments at future colliders are ...pushing for an optimization of all factors affecting the time resolution of the whole acquisition chain comprising the crystal, the photo detector, and the electronics. The time resolution of a scintillator-based detection system is determined by the rate of photo electrons at the detection threshold, which depends on the time distribution of photons being converted in the photo detector. The possibility to achieve time resolution of about 100 ps Full Width at Half Maximum (FWHM) requires an optimization of the light production in the scintillator, the light transport and its transfer from the scintillator to the photo detector. In order to maximize the light yield, and in particular the density of photons in the first nanosecond, while minimizing the rise time and decay time, particular attention must be paid to the energy transfer mechanisms to the activator as well as to the energy transition type at the activator ion. Alternatively other light emission mechanisms can be considered. We show that particularly Cerenkov emission can be used for this purpose. Special emphasis was put on the light transport within the crystal and at its interface with the photo detector. Since light is produced isotropically in the scintillator the detector geometry must be optimized to decrease the optical path-length to the photo detector. Moreover light bouncing within the scintillator, affecting about 70% of the photons generated in currently used crystals, must be reduced as much as possible. We also investigate photonics crystals that are specifically designed to favor specific light propagation modes at the limit of total reflection inside and outside of the crystal and how they might increase the light transfer efficiency to the photo detector and hence improve time resolution. Examples for the production and deposition of photonics crystals as layers on Lutetium Yttrium Ortho-Silicate (LYSO) and Lutetium Yttrium Aluminum Perovskite (LuYAP) crystals are shown here, as well as first results on an improved light extraction resulting from this method.
Time of flight (TOF) measurements in positron emission tomography (PET) are very challenging in terms of timing performance, and should ideally achieve less than 100 ps FWHM precision. We present a ...time-based differential technique to read out silicon photomultipliers (SiPMs) which has less than 20 ps FWHM electronic jitter. The novel readout is a fast front end circuit (NINO) based on a first stage differential current mode amplifier with 20 Ω input resistance. Therefore the amplifier inputs are connected differentially to the SiPM's anode and cathode ports. The leading edge of the output signal provides the time information, while the trailing edge provides the energy information. Based on a Monte Carlo photon-generation model, HSPICE simulations were run with a 3 × 3 mm 2 SiPM-model, read out with a differential current amplifier. The results of these simulations are presented here and compared with experimental data obtained with a 3 × 3 × 15 mm 3 LSO crystal coupled to a SiPM. The measured time coincidence precision and the limitations in the overall timing accuracy are interpreted using Monte Carlo/SPICE simulation, Poisson statistics, and geometric effects of the crystal.
SiPM time resolution: From single photon to saturation Gundacker, S.; Auffray, E.; Di Vara, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2013, Volume:
718
Journal Article
Peer reviewed
The time resolution of photon detection systems is important for a wide range of applications in physics and chemistry. It impacts the quality of time-resolved spectroscopy of ultrafast processes and ...has a direct influence on the best achievable time resolution of time-of-flight detectors in high-energy and medical physics. For the characterization of photon detectors, it is important to measure their exact timing properties in dependence of the photon flux and the operational parameters of the photodetector and its accompanying electronics. We report on the timing of silicon photomultipliers (SiPM) as a function of their bias voltage, electronics threshold settings and the number of impinging photons. We used ultrashort laser pulses at 400nm wavelength with pulse duration below 200fs. We focus our studies on different types of SiPMs (Hamamatsu MPPC S10931-025P, S10931-050P and S10931-100P) with different SPAD sizes (25μm, 50μm and 100μm) coupled to the ultrafast discriminator amplifier NINO. For the SiPMs, an optimum in the time resolution regarding bias and threshold settings can be reached. For the 50μm type, we achieve a single photon time resolution of 80ps sigma, and for saturating photon fluxes better than 10ps sigma.
We discuss design issues related to the extensive use of Enclosed Layout Transistors (ELT's) and guard rings in deep submicron CMOS technologies in order to improve radiation tolerance of ASIC's ...designed for the LHC experiments (the Large Hadron Collider at present under construction at CERN). We present novel aspects related to the use of ELT's: noise measured before and after irradiation up to 100 Mrad (SiO/sub 2/), a model to calculate the W/L ratio and matching properties of these devices. Some conclusions concerning the density and the speed of IC's conceived with this design approach are finally drawn.
A study of the single photon time resolution (SPTR) and the coincidence time resolution (CTR) of the 4×4 MPPC array of Hamamatsu (S11827) has been performed to characterise the difference in signal ...response of an array compared to a single cell MPPC device. The monolithic 16-channel array has outputs from the 16 individual anodes and a common cathode. The common cathode has the disadvantage that a signal in any one of the 16 cells is coupled to the others. This is a source of cross-talk and also generates noise in the common ground affecting the timing performance of the array. The dependence of the SPTR on the applied bias voltage, the threshold and the laser intensity was first measured with a single 3×3mm2 MPPC (10963-50P) since it is the basic element of the 4×4 MPPC array. The results show that when only a single cell of the array is connected (with all other cells ‘off’, i.e. with the anodes disconnected) the MPPC array response is much like the single-cell MPPC with an SPTR of 110ps (sigma). We then tested the performance of the 4×4 array, incrementing the number of active cells in the array. Increasing the number of MPPC cells decreases the signal (measured by time-over-threshold) leading to a worsening of the SPTR proportional to the number of active MPPC cells. The merit of the differential readout for timing becomes evident when we compare the observed SPTR value of the MPPC-matrix with that of the single-ended readout. This improvement is also confirmed by the CTR measurement results. We measured the timing characteristics of the array using a 4×4 LYSO crystal matrix (3×3×15mm3 per cell). The improvement in CTR (FWHM) from 283ps to 226ps is obtained by implementing the differential readout scheme. The results suggest that for critical timing applications, a differential output from each individual cell is an advantage.
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