Method for improving the time resolution of a TOF system

In order to study the possibility of improving the timing performance of the time of flight （TOF） systems, which are made of plastic scintillator counters, and read out by photomultiplier tubes （PMT） with mesh dynodes and conventional electronics, we have conducted a study using faster PMTs and ultra fast waveform digitizers to read out the plastic scintillators. Different waveform analysis methods are used to calculate the time resolution of such a system. Results are compared with the conventional discriminating method based on a threshold and pulse height. Our tests and analysis show that significant timing performance improvements can be achieved by using this new system.

A cosmic ray test platform based on high time resolution MRPC technology

In order to test the performance of detector prototypes in a laboratory environment, we design and build a large area （90 crux52 cm） test platform for cosmic rays based on a well-designed Multi-gap Resistive Plate Chamber （MRPC） with excellent time resolution and a high detection efficiency for minimum ionizing particles. The time resolution of the MRPC module used is tested to be -80 ps, and the position resolution along the strip is -5 mm, while the position resolution perpendicular to the strip is -12.7 ram. The platform constructed by four MRPC modules can be used for tracking cosmic rays with a spatial resolution of -6.3 mm, and provide a reference time -40 ps.

Determination of the time resolution for neutron scintillation detectors by multi-coincidence measurement

Based on the multi-coincidence measurement, the time resolution of three liquid scintillation detectors （BC501A） were determined strictly by solving the coincidence equations, where the influence from electronics estimated by self coincidence measurement as well as the background had been considered. The result of this work agreed well with the result that was deduced from the traditional method, and it will be helpful to analyze the energy resolution of neutron time of flight spectra measured by using such detectors at CIAE （China Institute of Atomic Energy）.

Characteristics and time resolutions of two CeBr_(3) gamma-ray spectrometers

Purpose The purpose of this work is to study the pulse shape,energy resolution,non-proportionality of energy response for gamma-rays,and time characteristics of CeBr_(3) detector.Method The time and energy responses of two CeBr_(3) detectors were characterized by an analog method and a digital method using a set of standardγ-ray sources.The pulse shape,energy resolution and non-proportionality(nPR)of energy response forγ-rays were characterized using the analog method.For the analog method,the high voltage applied to PMTs,parameters of walk and external delay of constant fraction discriminator were optimized.For the digital method,a CEAN 1729A digitizer with sampling frequency of 2 GS/s and resolution of 11 bit,and a digital constant fraction discrimination technique were used to study the time performance of the two CeBr_(3) detectors.Then,the coincidence time resolutions of the CeBr_(3) detectors for the gamma peaks of ^(22)Na and ^(60)Co were measured using the two methods.Results The t_(rise),lifetimeτ,t_(fall) for CeBr_(3)21^(#)and 22^(#)are 11.2 ns,23.8 ns,50.2 ns,and 10.4 ns,26.5 ns,58.6 ns,respectively.The measured non-proportionality of CeBr_(3)21^(#)and 22^(#)are 1.08%and 2.22%,respectively.The time resolutions of the two CeBr_(3) detectors are 244±2 ps and 248±3 ps at the energy peaks of ^(60)Co source,and 336±2 ps and 335±3 ps at 511 keV for the analog and the digital methods.Conclusions The time resolutions obtained by the analog method and the digital method are almost identical.The CeBr_(3) detector is a good option in the applications such as half-life measurements,ToF-PET and high counting rate conditions.Furthermore,it is a goodγ-ray spectrometer owing to the preferable energy resolution and non-internal activity.

Simulation research on time resolution based on Cherenkov radiation

Purpose A faster time performance can be achieved by focusing on prompt emitted photons,such as Cherenkov photons.In this study,the time fluctuations of Cherenkov photons transmission in the three Cherenkov radiators were first simulated,and we evaluated the detector performance and discussed ways to improve the coincidence time resolution(CTR)results for the detector with the three radiators.Finally,we compared detection efficiency of Cherenkov radiation in three radiators.Methods In this work,we recorded the step-by-step information of Cherenkov photons and the electrons that produced them in the radiator,information of photons on the photon outputting surface,and the step-by-step information tracing of the par-ent charged particles(electrons)to evaluate the factors influencing the performance time of the detector based on Geant4.Specially,we usually use a photon amplitude timing in the experimental implements,and the arrival time of an event is defined as the arrival time of the first photon of the event accordingly.Results The time fluctuations of Cherenkov photons transmission in the three Cherenkov radiators with a 5 mm length were simulated as 28.5 ps for PbF,40.1 ps for PbWO_(4),and 24.7 ps for Al_(2)O_(3).After considering other factors such as quantum efficiency(QE)of 30%and transit time spread(TTS)of 10 ps from the process of practical electronics,the CTR of a pair of single-pixel detectors were 56.6 ps for PbF_(2),78.8 ps for PbWO_(4),and 46.3 ps for Al_(2)O_(3) with a thickness of 5 mm.The detection efficiency of PbF_(2) is 32.25%,PbWO_(4) of 31.91%and Al_(2)O_(3) of 8.14%in the case of 5 mm length.Conclusions The simulation results indicated that using the Cherenkov photons produced in PbF_(2),PbWO_(4),Al_(2)O_(3) for detec-tor timing can obtain good CTR results.In this study,it demonstrates that it is possible to achieve a pretty good CTR with an improved QE and a reduced TTS of the photodetector.

Time-resolution enhanced multi-path OTD measurement using an adaptive filter based incoherent OFDR

High accuracy and time resolution optical transfer delay(OTD)measurement is highly desired in many multi-path applications,such as optical true-time-delay-based array systems and distributed optical sensors.However,the time resolution is usually limited by the frequency range of the probe signal in frequency-multiplexed OTD measurement techniques.Here,we proposed a time-resolution enhanced OTD measurement method based on incoherent optical frequency domain reflectometry(I-OFDR),where an adaptive filter is designed to suppress the spectral leakage from other paths to break the resolution limitation.A weighted least square(WLS)cost function is first established,and then an iteration approach is used to minimize the cost function.Finally,the appropriate filter parameter is obtained according to the convergence results.In a proof-of-concept experiment,the time-domain response of two optical links with a length difference of 900 ps is successfully estimated by applying a probe signal with a bandwidth of 400 MHz.The time resolution is improved by 2.78times compared to the theoretical resolution limit of the inverse discrete Fourier transform(iDFT)algorithm.In addition,the OTD measurement error is below±0.8 ps.The proposed algorithm provides a novel way to improve the measurement resolution without applying a probe signal with a large bandwidth,avoiding measurement errors induced by the dispersion effect.

Resolution Enhancement in Ultrasonic TOFD Imaging by Combining Sparse Deconvolution and Synthetic Aperture Focusing Technique(Sparse-SAFT)

The shallow subsurface defects are difficult to be identified and quantified by ultrasonic time-of-flight diffraction(TOFD)due to the low resolution induced by pulse width and beam spreading.In this paper,Sparse-SAFT is proposed to improve the time resolution and lateral resolution in TOFD imaging by combining sparse deconvolution and synthetic aperture focusing technique(SAFT).The mathematical model in the frequency domain is established based on the l1 and l2 norm constraints,and the optimization problem is solved for enhancing time resolution.On this basis,SAFT is employed to improve lateral resolution by delay-and-sum beamforming.The simulated and experimental results indicate that the lateral wave and tip-diffracted waves can be decoupled with Sparse-SAFT.The shallow subsurface defects with a height of 3.0 mm at the depth of 3.0 mm were detected quantitatively,and the relative measurement errors of flaw heights and depths were no more than 10.3%.Compared to conventional SAFT,the time resolution and lateral resolution are enhanced by 72.5 and 56%with Sparse-SAFT,respectively.Finally,the proposed method is also suitable for improving resolution to detect the defects beyond dead zone.

Picosecond time-resolved X-ray ferromagnetic resonance measurements at Shanghai synchrotron radiation facility

An experimental picosecond time-resolved X-ray ferromagnetic resonance(TR-XFMR)apparatus with a time resolution of 13 ps(RMS)or 31 ps(FWHM)was constructed and demonstrated in the 07U and 08U1A soft X-ray beamlines at the Shanghai Synchrotron Radiation Facility(SSRF)using pump-probe detection and X-ray magnetic circular dichroism(XMCD)spectroscopy.Element and time-resolved ferromagnetic resonance was excited by continuous microwave phase-locking of the bunch clock within the photon beam during synchrotron radiation and was characterized by detecting the magnetic circular dichroism signals of the elements of interest in the magnetic films.Using this equipment,we measured the amplitude of the element-specific moment precession during ferromagnetic resonance(FMR)at 2 GHz in a single Ni81Fe19layer.

Simulation of time bunching for a pulsed positron beam

Simulate anneal arithmetic has been used to settle the problem of time bunching on a pulsed slow-positron beam device. This paper has searched for the parameters of the device in a large scope and achieved the time resolution within 150ps at the target with accelerating voltage in a range of 0.5-30kV.

High-Resolution Traffic Flow Prediction Model Based on Deep Learning

The time resolution of the existing traffic flow prediction model is too big to be applied to adaptive signal timing optimization.Based on the view of the platoon dispersion model,the relationship between vehicle arrival at the downstream intersection and vehicle departure from the upstream intersection was analyzed.Then,a high-resolution traffic flow prediction model based on deep learning was developed.The departure flow rate from the upstream and the arrival flow rate at the downstream intersection was taking as the input and output in the proposed model,respectively.Finally,the parameters of the proposed model were trained by the field data,and the proposed model was implemented to forecast the arrival flow rate of the downstream intersection.Results show that the proposed model can better capture the fluctuant traffic flow and reduced MAE,MRE,and RMSE by 9.53%,39.92%,and 3.56%,respectively,compared with traditional models and algorithms,such as Robert­son's model and artificial neural network.Therefore,the proposed model can be applied for realtime adaptive signal timing optimization.

Design and performance of a high-speed and low-noise preamplifier for SiPM

Considering the R&D for upgrading the K^(0)_(L) andμdetectors in the Belle II experiment using a scintillator and silicon pho-tomultiplier(SiPM),we designed a compact high-speed and low-noise preamplifier.The preamplifier demonstrated a good gain stability,bandwidth of 426 MHz,baseline noise level ofσ≈0.6 mV,dynamic range of up to170 mV of the input signal amplitude,good time resolution of 20 ps,and it can be comprehensively applied to SiPMs.Adopting pole-zero-cancelation in the preamplifier reduces both the rise and fall times of the SiPM signal,which can significantly improve the time resolution and reduce the pile-up when using a large SiPM or an array of SiPMs.Various combinations of the preamplifier and several types of SiPMs demonstrated time resolutions better than 50 ps for most cases;when the number of detected photons was larger than 60,a time resolution of approximately 25 ps was achieved.

LCT和GCT联合鉴别未知水样中N,N-二烷基氨基乙基磺酸及其类似物

N,N-dialkylaminoethane-2-sulfonic acids are environmental marker compounds of V type nerve agents,hence analysis of them is very important for verification of the chemical weapons convention(CWC).In this article,liquid chromatography-high resolution time of flight mass spectrometry coupled with accurate mass measurement were used to discriminate N,N-disopropyl aminoethane-2-sulfonic acid and a CWC non-related compound 3-(N-Morpholino)propanesulfonic acid in Water.The method was fast,simple and accurate,proving that high resolution mass spectrometry is a good technique for the analysis of unknown toxicant.

Development of a wide-range and fast-response digitizing pulse signal acquisition and processing system for neutron flux monitoring on EAST

The neutron count rate fluctuation reaches six orders of magnitude between the ohmic plasma scenario and high power of auxiliary heating on an experimental advanced superconducting tokamak(EAST).The measurement result of neutron flux monitoring(NFM)is a significant feedback parameter related to the acquisition of radiation protection-related information and rapid fluctuations in neutron emission induced by plasma magnetohydrodynamic activity.Therefore,a wide range and high time resolution are required for the NFM system on EAST.To satisfy these requirements,a digital pulse signal acquisition and processing system with a wide dynamic range and fast response time was developed.The present study was conducted using a field-programmable gate array(FPGA)and peripheral component interconnect extension for instrument express(PXIe)platform.The digital dual measurement modes,which are composed of the pulse-counting mode and AC coupled square integral's Campbelling mode,were designed to expand the measurement range of the signal acquisition and processing system.The time resolution of the signal acquisition and processing system was improved from 10 to 1 ms owing to utilizing highspeed analog-to-digital converters(ADCs),a high-speed PXIe communication with a direct memory access(DMA)mode,and online data preprocessing technology of FPGA.The signal acquisition and processing system was tested experimentally in the EAST radiation field.The test results showed that the time resolution of NFM was improved to 1 ms,and the dynamic range of the neutron counts rate was expanded to more than 10^(6) counts per second.The Campbelling mode was calibrated using a multipoint average linear fitting method;subsequently,the fitting coefficient reached 0.9911.Therefore,the newly developed pulse signal acquisition and processing system ensures that the NFM system meets the requirements of high-parameter experiments conducted on EAST more effectively.

Rollback reconstruction for TDC enhanced perfusion imaging

Tomographic perfusion imaging is a significant imaging modality for stroke diagnosis.However,the low rotational speed of the C-arm(6–8 s per circle)is a challenge for applying perfusion imaging in C-arm cone beam computed tomography(CBCT).Traditional reconstruction methods cannot remove the artifacts caused by the slow rotational speed or acquire enough sample points to restore the time density curve(TDC).This paper presents a dynamic rollback reconstruction method for CBCT.The proposed method can improve the temporal resolution by increasing the sample points used for calculating the TDC.Combined with existing techniques,the algorithm allows slow-rotating scanners to be used for perfusion imaging purposes.In the experiments,the proposed method was compared with other dynamic reconstruction algorithms based on standard reconstruction and the temporal interpolation approach.The presented algorithm could improve the temporal resolution without increasing the X-ray exposure time or contrast agent.

Meaningful Contact Estimates among Children in a Childcare Centre with Applications to Contact Matrices in Infectious Disease Modelling

We present a mathematical model of a day care center in a developed country (such as Canada), in order to use it for the estimation of individual-to-individual contact rates in young age groups and in an educational group setting. In our model, individuals in the population are children (ages 1.5 to 4 years) and staff, and their interactions are modelled explicitly: person-to-person and person-to-environment, with a very high time resolution. Their movement and meaningful contact patterns are simulated and then calibrated with collected data from a child care facility as a case study. We present these calibration results as a first part in the further development of our model for testing and estimating the spread of infectious diseases within child care centers.

Urinary metabonomics of stomach cancer assessed by rapid resolution liquid chromatography/time-of-flight mass spectrometry

Background Stomach cancer is among the most commonly occurring malignancies worldwide. It would be beneficial to develop a urine-based assay whereby patients with undiagnosed stomach cancer could be screened and their cancer detected in the eadiest stages. Methods A urinary metabonomics method based on ultra-performance liquid chromatography combined with quadruple time-of-flight mass spectrometry was used to analyze urine samples from patients with stomach cancer and healthy controls. Results Statistical analysis revealed a clear separation of patients and healthy controls using the aforementioned methodology. Some significantly changed metabolites were identified. Conclusions Use of the metabonomics method in patients with stomach cancer could effectively detect distinct changes in urinary metabolites and had the capacity to detect cancer; therefore, it may be a valuable tool in earlier diagnosis. Furthermore, the detection and identification of altered metabolites in the current study may help elucidate possible mechanisms involved in stomach cancer.

A new method of aperture synthetizing in digital holography

This paper proposes a new method of aperture synthetizing in digital holography based on the principle of holography.In the new method aperture synthetizing is achieved by reconstructing each sub-hologram respectively,firstly,moving each reconstructed wave field referred to the benchmark reconstructed wave field according to the relationship between spacial motion and frequency shift,and finally splicing them by using superposition. Two different recording ways,using plane wave to record and using spherical wave to record,are analyzed,and their moving formula is deduced,too.Simulation and experiment are done. The results show that in comparison with the traditional method of aperture synthetizing in digital holography,the new method can decrease calculation and save reconstructed time obviously which has better applicability.

Reconstruction and transmission of astronomical image based on compressed sensing

In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compressed sensing（CS） theory was proposed, which has earned great concern as it can compress an image with a low compression rate, meanwhile the original image can be perfectly reconstructed from only a few compressed data. The CS theory is used to transmit the high resolution astronomical image and build the simulation environment where there is communication between the satellite and the Earth. Number experimental results show that the CS theory can effectively reduce the image transmission and reconstruction time. Even with a very low compression rate, it still can recover a higher quality astronomical image than JPEG and JPEG-2000 compression methods.

Plastic scintillation detectors for precision Time-of-Flight measurements of relativistic heavy ions

Plastic scintillation detectors for Time-of-Flight（TOF） measurements are almost essential for event-byevent identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of dimensions50×50×3^t mm^3and 80×100×3^t mm^3have been set up at the External Target Facility（ETF）, Institute of Modern Physics（IMP）. Their time, energy and position responses are measured with the^（18）O primary beam at 400 Me V/nucleon. After off-line corrections for walk effect and position, the time resolutions of the two detectors are determined to be 27 ps（σ） and 36 ps（σ）, respectively. Both detectors have nearly the same energy resolution of3.1%（σ） and position resolution of about 3.4 mm（σ）. The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading the RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.

BESⅢ barrel time-of-flight (TOF) calibration using cosmic ray data

The principle of the method for the BESIII TOF calibration using cosmic ray data without magnetic field are reported in this paper. After applying calibration constants, the single-end readout time resolution could reach about 150 ps, and the time resolution for one layer is achieved to be about 110 ps. The paper also described the extraction scheme for the event start time of cosmic events.