Constant Fraction Timing Research Articles

Comparison of timing discrimination method for pulse-based Lidar

Time discrimination methods of pulse signals serve as the foundation for ranging, identification, and precision in pulse Lidar. Therefore, employing a judicious time discrimination method is pivotal in enhancing Lidar overall performance. This study initially delves into the theoretical distinctions among various time discrimination methods, including constant fraction timing, waveform centroid, dual-threshold waveform, and amplitude with rising edge compensation timing. It meticulously analyzes and compares these diverse methods for time discrimination. Subsequently, employing these methodologies to process Lidar echo signals to contrast their time measurement accuracy. The conclusions will provide valuable guidance for the design and practical application of pulse-type Lidar systems.

Time of flight detector for charged particle identification based on circular electron-positron collider

The circular electron-positron collider (CEPC) requires a 3% precision in the measurement of d<i>E</i>/d<i>x</i> to identify long-lived charged particles. However, the measurement of d<i>E</i>/d<i>x</i> has a blind area for each of charged particles of <inline-formula><tex-math id="M8">\begin{document}$\pi / \rm{K}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M8.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M9">\begin{document}$\pi / \rm{P}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M9.png"/></alternatives></inline-formula>, and <inline-formula><tex-math id="M10">\begin{document}$\rm{K} / \rm{P}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M10.png"/></alternatives></inline-formula>, having transverse momenta of 1 GeV/<i>c</i>, 1.6 GeV/<i>c</i>, and 2 GeV/<i>c</i> respectively. One potential solution is to use a high-precision time-of-flight (TOF) detector with a time resolution of less than 50 ps to fill in the blind area. To address this, we propose a small particle TOF detector that uses small plastic scintillators (<inline-formula><tex-math id="M11">\begin{document}$1 \;\; \mathrm{cm} \times 1 \;\; \mathrm{cm} \times 0.3 \;\; \mathrm{cm}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M11.png"/></alternatives></inline-formula>) silicon photomultipliers for readout. In this work, we introduce the construction of the detector and calibrate its performance by using <inline-formula><tex-math id="M12">\begin{document}${ }^{90} \mathrm{Sr} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M12.png"/></alternatives></inline-formula> electron collimators and high-speed waveform acquisition electronics. Using a constant fraction timing method, we find that the time resolution of the detector is about 48 ps, satisfying the CEPC’s requirements for TOF detection.

White Rabbit Time Synchronization for Radiation Detector Readout Electronics

As radiation detector arrays in nuclear physics applications become larger and physically more separated, the time synchronization and trigger distribution between many channels of detector readout electronics become more challenging. Clocks and triggers are traditionally distributed through dedicated cabling, but newer methods such as the IEEE 1588 Precision Time Protocol and White Rabbit allow clock synchronization through the exchange of timing messages over Ethernet. Consequently, we report here the use of White Rabbit in a new detector readout module, the Pixie-Net XL. The White Rabbit core, data capture from multiple digitizing channels, and subsequent pulse processing for pulse height and constant fraction timing are implemented in a Kintex 7 FPGA. The detector data records include White Rabbit time stamps and are transmitted to storage through the White Rabbit core's gigabit Ethernet data path or a slower diagnostic/control link using an embedded Zynq processor. The performance is characterized by time-of-flight style measurements and by time correlation of high energy background events from cosmic showers in detectors separated by longer distances. Software for the Zynq processor can implement "software triggering", for example to limit recording of data to events where a minimum number of channels from multiple modules detect radiation at the same time.

Implementation of digital constant fraction timing based on field programmable gate array

Compared with analog circuits, FPGA(Field Programmable Gate Array) had the advantages of redevelopment and low cost. Compared with MCU, FPGA used hardware description language to construct the circuit, which had the advantages of simple structure and fast parallel operation speed. In this paper, the simulation of digital Constant Fraction Timing can be realized based on FPGA, and the feasibility and accuracy of the design can be proved by using the simulation waveform of Modelsim and the waveform can be captured by signaltap. Modelsim can verify the correctness of the timing between modules, and signaltap can verify the actual running effect of the program on the board.

The time shift between the neutron and [formula omitted]-ray timestamps in organic stilbene scintillator

It is shown that the use of the standard constant fraction timing method for obtaining timestamps of signals from an organic stilbene scintillator leads to a systematic difference in timestamps when detecting neutrons and γ-rays. A detailed study of this effect was carried out using a digital time-of-flight spectrometer based on a stilbene detector and a pulsed source of quasi-monoenergetic neutrons based on the 2H(d,n)3He reaction. It is shown that this effect is present for the entire range of crystal light output values and is related to the difference in the rise time of signals induced by neutrons and γ-rays. It is demonstrated that this effect can lead to a systematic error in absolute measurements of the prompt fission neutron spectra using the time-of-flight method with conventional analog constant fraction timing. A method for compensating this systematic shift based on the analysis of the timestamps position for the digital signals at the different values of the constant fraction is suggested.

Investigation of digital timing resolution and further improvement by using constant fraction signal time marker slope for fast scintillator detectors

A digital timing algorithm is explored for fast scintillator detectors, viz. LaBr3, BaF2, and BC501A. Signals were collected with CAEN 250 mega samples per second (MSPS) and 500 MSPS digitizers. The zero crossing time markers (TM) were obtained with a standard digital constant fraction timing (DCF) method. Accurate timing information is obtained using cubic spline interpolation of a DCF transient region sample points. To get the best time-of-flight (TOF) resolution, an optimization of DCF parameters is performed (delay and constant fraction) for each pair of detectors: (BaF2-LaBr3), (BaF2-BC501A), and (LaBr3-BC501A). In addition, the slope information of an interpolated DCF signal is extracted at TM position. This information gives a new insight to understand the broadening in TOF, obtained for a given detector pair. For a pair of signals having small relative slope and interpolation deviations at TM, leads to minimum time broadening. However, the tailing in TOF spectra is dictated by the interplay between the interpolation error and slope variations. Best TOF resolution achieved at the optimum DCF parameters, can be further improved by using slope parameter. Guided by the relative slope parameter, events selection can be imposed which leads to reduction in TOF broadening. While the method sets a trade-off between timing response and coincidence efficiency, it provides an improvement in TOF. With the proposed method, the improved TOF resolution (FWHM) for the aforementioned detector pairs are; 25% (0.69 ns), 40% (0.74 ns), 53% (0.6 ns) respectively, obtained with 250 MSPS, and corresponds to 12% (0.37 ns), 33% (0.72 ns), 35% (0.69 ns) respectively with 500 MSPS digitizers. For the same detector pair, event survival probabilities are; 57%, 58%, 51% respectively with 250 MSPS and becomes 63%, 57%, 68% using 500 MSPS digitizers.

Readout electronics for a high-resolution soft X-ray spectrometer based on silicon drift detector

The readout electronics for a prototype soft X-ray spectrometer based on silicon drift detector (SDD), for precisely measuring the energy and arrival time of X-ray photons is presented in this paper. The system mainly consists of two parts, i.e., an analog electronics section (including a pre-amplifier, a signal shaper and filter, a constant fraction timing circuit, and a peak hold circuit) and a digital electronics section (including an ADC and a TDC). Test results with X-ray sources show that an energy dynamic range of 1–10 keV with an integral nonlinearity of less than 0.1% can be achieved, and the energy resolution is better than 160 eV @ 5.9 keV FWHM. Using a waveform generator, test results also indicate that time resolution of the electronics system is about 3.7 ns, which is much less than the transit time spread of SDD (<100 ns) and satisfies the requirements of future applications.

The experimental set-up of the RIB in-flight facility EXOTIC

We describe the experimental set-up of the Radioactive Ion Beam (RIB) in-flight facility EXOTIC consisting of: (a) two position-sensitive Parallel Plate Avalanche Counters (PPACs), dedicated to the event-by-event tracking of the produced RIBs and to time of flight measurements and (b) the new high-granularity compact telescope array EXPADES (EXotic PArticle DEtection System), designed for nuclear physics and nuclear astrophysics experiments employing low-energy light RIBs. EXPADES consists of eight ΔE–Eres telescopes arranged in a cylindrical configuration around the target. Each telescope is made up of two Double Sided Silicon Strip Detectors (DSSSDs) with a thickness of 40/60μm and 300μm for the ΔE and Eres layer, respectively. Additionally, eight ionization chambers were constructed to be used as an alternative ΔE stage or, in conjunction with the entire DSSSD array, to build up more complex triple telescopes. New low-noise multi-channel charge-sensitive preamplifiers and spectroscopy amplifiers, associated with constant fraction discriminators, peak-and-hold and Time to Amplitude Converter circuits were developed for the electronic readout of the ΔE stage. Application Specific Integrated Circuit-based electronics was employed for the treatment of the Eres signals. An 8-channel, 12-bit multi-sampling 50MHz Analog to Digital Converter, a Trigger Supervisor Board for handling the trigger signals of the whole experimental set-up and an ad hoc data acquisition system were also developed. The performance of the PPACs, EXPADES and of the associated electronics was obtained offline with standard α calibration sources and in-beam by measuring the scattering process for the systems 17O+58Ni and 17O+208Pb at incident energies around their respective Coulomb barriers and, successively, during the first experimental runs with the RIBs of the EXOTIC facility.

A method to enhance coincidence time resolution with applications for medical imaging systems (TOF/PET)

A coincidence timing spectrometer was assembled using NaI(Tl) inorganic and BC418 type organic (plastic) scintillation detectors. The constant fraction timing method was used. Coincidence time resolution values of the detectors, which have great importance in TOF/PET measurements, were obtained separately. The resolutions were enhanced using a different method in a start-stop coincidence spectrometer: the signals from the start detectors were delayed. The results from the FLUKA Monte Carlo simulation code agreed well with the experimental results.

Timing Applications to Improve the Energy Resolution of NaI(Tl) Scintillation Detectors

Gamma-ray energy resolution of a NaI(Tl) inorganic scintillation detector was improved in the present work. For this purpose, leading edge and constant fraction timing methods were used. Gamma energy spectrum of the radioisotope (<SUP>137</SUP>Cs) and the time spectra through these timing methods were obtained separately. Energy spectrum was gated with both time spectra, and the obtained results were compared with each other. Energy resolution enhancements of 3.5% and 7.5% on the photopeak of the radioisotope were obtained through leading edge and constant fraction timing methods, respectively. Energy resolution value from constant fraction timing was better than that of leading edge timing method.

Pulse pile-up recovery for the front-end electronics of the PANDA Electromagnetic Calorimeter

At the future Facility for Antiproton and Ion Research near Darmstadt in Germany the PANDA detector will be employed to study the charmonium spectrum and to search for narrow exotic hadronic states, predicted by Quantum Chromodynamics. In the PANDA experiment, 1.5 to 15 GeV/c anti-protons will annihilate with a hydrogen target at an average rate of 20MHz. Among the sub-detectors of PANDA is the Electromagnetic Calorimeter (EMC) planned for the studies of electromagnetic transitions and neutral meson decays. Due to the high annihilation rates, the EMC will be exposed to single-detector hit rates up to 500kHz, which may lead to pulse overlap. Hence, to recover the energy and time information of the overlapping pulses, a pulse pile-up recovery method is developed. The method is easy to implement in FPGA for online data processing. The Constant Fraction Timing algorithm is applied at the trailing edge to determine the time stamp of pile-up pulses. The energy and the time information of pile-up pulses can be recovered up to time differences of 50ns, equal to the pulse rise-time, in a large dynamic energy range.

Time resolution investigations for general purpose plastic scintillation detectors in different thicknesses

Time spectra of 90Sr, 137Cs and 207Bi radioactive sources were obtained by using a BC 400 type plastic scintillation detectors in different thicknesses. Time resolution values through the time spectra were obtained by means of leading edge and constant fraction timing methods. The obtained time resolution values from leading edge method were compared with those of constant fraction timing method.

Alpha energy resolution enhancement of a Si surface barrier detector

In this work, alpha energy resolution of a Si surface barrier detector was improved. For this purpose, we used constant fraction timing method. Energy resolution enhancement of about 1 % was achieved for alpha peak of 210Po. In order to prove the validity of the timing method, it was applied to the alpha spectrum of 226Ra. It was concluded that proposed method was successful on the energy resolution improvement.

Alpha energy resolution improvement of a general purpose plastic scintillation detector

Alpha energy spectra of 210Po and 226Ra radioactive sources were achieved by using a BC400 type plastic scintillation detector. In order to enhance the energy resolution of the detector, constant fraction timing method was used. Obtained results showed that the used timing method was successful on improving the energy resolution of the detector with the amendment of about 1 % even at the low count rates.

Energy resolution improvement of NaI(Tl) scintillation detectors by means of a timing discrimination method

Gamma-ray energy spectrum of a 137Cs radioisotope was obtained by using a NaI(Tl) scintillation detector. Improvement of the energy resolution of the detector was aimed. To achieve this, constant fraction timing method was used. Energy resolution of the photopeak of the isotope was improved from 7.1 to 6.7% through the timing application.

Research of the navigation accuracy for the X-ray pulsar navigation system

In order to improve the navigation accuracy of the X-ray pulsar navigation system, in this paper we propose a constant fraction timing method based on the low-pass filter to measure the arrival time of the X-ray pulse in X-ray pulsar navigation. According to the technical scheme, the timing accuracies and dead times of original peaking timing and the improved constant fraction timing are measured. Experimental results indicate that the timing accuracy and the dead time of the peaking timing system are 18 ns and 4750 ns, the timing accuracy and the dead time of the constant fraction timing system are 0.78 ns and 105 ns. The timing accuracy and the dead time of constant fraction timing system are significantly improved compared with those of the peaking timing system. In the X-ray pulsar navigation system, the cumulative pulse profile of the X-ray pulse is constructed in the two different timing systems through measuring the arrival time of the X-ray photon. Experimental results indicate that compared with using the peaking timing system, the cumulative pulse profile of the X-ray pulse using the improved constant fraction timing system is improved obviously, therefore, the navigation accuracy could be improved by using the constant fraction timing system.

Free-running ADC- and FPGA-based signal processing method for brain PET using GAPD arrays

Currently, for most photomultiplier tube (PMT)-based PET systems, constant fraction discriminators (CFD) and time to digital converters (TDC) have been employed to detect gamma ray signal arrival time, whereas anger logic circuits and peak detection analog-to-digital converters (ADCs) have been implemented to acquire position and energy information of detected events. As compared to PMT the Geiger-mode avalanche photodiodes (GAPDs) have a variety of advantages, such as compactness, low bias voltage requirement and MRI compatibility. Furthermore, the individual read-out method using a GAPD array coupled 1:1 with an array scintillator can provide better image uniformity than can be achieved using PMT and anger logic circuits. Recently, a brain PET using 72 GAPD arrays (4×4 array, pixel size: 3 mm×3 mm) coupled 1:1 with LYSO scintillators (4×4 array, pixel size: 3 mm×3 mm×20 mm) has been developed for simultaneous PET/MRI imaging in our laboratory. Eighteen 64:1 position decoder circuits (PDCs) were used to reduce GAPD channel number and three off-the-shelf free-running ADC and field programmable gate array (FPGA) combined data acquisition (DAQ) cards were used for data acquisition and processing. In this study, a free-running ADC- and FPGA-based signal processing method was developed for the detection of gamma ray signal arrival time, energy and position information all together for each GAPD channel. For the method developed herein, three DAQ cards continuously acquired 18 channels of pre-amplified analog gamma ray signals and 108-bit digital addresses from 18 PDCs. In the FPGA, the digitized gamma ray pulses and digital addresses were processed to generate data packages containing pulse arrival time, baseline value, energy value and GAPD channel ID. Finally, these data packages were saved to a 128 Mbyte on-board synchronous dynamic random access memory (SDRAM) and then transferred to a host computer for coincidence sorting and image reconstruction. In order to evaluate the functionality of the developed signal processing method, energy and timing resolutions for brain PET were measured via the placement of a 6 μCi 22Na point source at the center of the PET scanner. Furthermore the PET image of the hot rod phantom (rod diameter: from 2.5 mm to 6.5 mm) with activity of 1 mCi was simulated, and then image acquisition experiment was performed using the brain PET. Measured average energy resolution for 1152 GAPD channels and system timing resolution were 19.5% (FWHM%) and 2.7 ns (FWHM), respectively. With regard to the acquisition of the hot rod phantom image, rods could be resolved down to a diameter of 2.5 mm, which was similar to simulated results. The experimental results demonstrated that the signal processing method developed herein was successfully implemented for brain PET. This reduced the complexity, cost and developing duration for PET system relative to normal PET electronics, and it will obviously be useful for the development of high-performance investigational PET systems.

A simplified digital positron lifetime spectrometer based on a fast digital oscilloscope

A simplified digital positron lifetime spectrometer is presented and tested. This system is only composed of two scintillation detectors, a time delayer and a digital oscilloscope. Both online and offline analysis of the detector signals can be optionally chosen to construct positron lifetime spectrum by histogramming the time difference between the positron birth signal of 1.27 MeV γ-ray and one positron annihilation signal of 0.511 MeV γ-rays. Several pulse discrimination methods and timing numerical algorithms are proposed and well applied to perform pulse energy discrimination and digital constant fraction timing (DCFT). A combination discrimination of pulse amplitude, pulse risetime and ratio of pulse area to pulse amplitude with DCFT is found able to achieve the best time resolution of 208 ps full-width at half-maximum (FWHM), which is much better over the analog spectrometer using the same detectors. This newly developed apparatus except for having better performance is particularly easy to be constructed and implemented.

Development of a 1 GS/s high-resolution sampling ADC system

Today, many experiments in high energy physics have to handle data rates of several MHz per readout channel to reach statistical significance for the measured quantities. In addition, these experiments frequently have to deal with short analog pulses of a few nanoseconds length which may cover large dynamic ranges and which require amplitude as well as time measurements with highest accuracy. For applications of this kind fast transient recorders with very high resolution and deep on-board memory are the first choice. We have built a 16-channel 12- or 14-bit single unit VME64x/VXS sampling ADC module which may sample at rates up to 1GS/s. Fast algorithms have been developed and successfully tested on scintillating counter detectors to implement pulse shape discrimination, constant fraction timing and gated integration.

Sample-interpolation timing: an optimized technique for the digital measurement of time of flight for γ rays and neutrons at relatively low sampling rates

A unique, digital time pick-off method, known as sample-interpolation timing (SIT) is described. This method demonstrates the possibility of improved timing resolution for the digital measurement of time of flight compared with digital replica-analogue time pick-off methods for signals sampled at relatively low rates. Three analogue timing methods have been replicated in the digital domain (leading-edge, crossover and constant-fraction timing) for pulse data sampled at 8 GSa s−1. Events arising from the 7Li(p, n)7Be reaction have been detected with an EJ-301 organic liquid scintillator and recorded with a fast digital sampling oscilloscope. Sample-interpolation timing was developed solely for the digital domain and thus performs more efficiently on digital signals compared with analogue time pick-off methods replicated digitally, especially for fast signals that are sampled at rates that current affordable and portable devices can achieve. Sample interpolation can be applied to any analogue timing method replicated digitally and thus also has the potential to exploit the generic capabilities of analogue techniques with the benefits of operating in the digital domain. A threshold in sampling rate with respect to the signal pulse width is observed beyond which further improvements in timing resolution are not attained. This advance is relevant to many applications in which time-of-flight measurement is essential.