Time-of-flight Measurement System Research Articles

The FFIS spectrometer for determination of fission fragment mass distribution with the energy–velocity method

The FFIS spectrometer (Fission Fragment Identification Spectrometer) for determining independent fission yields has been developed based on the E–v method. By directly measuring the time-of-flight (TOF) and kinetic energy of fission fragments on their flight path, the post-neutron-emission mass yield distributions can be obtained. With the aim of getting the highest possible mass resolution, an axial grid ionization chamber and a TOF measurement system based on microchannel plate (MCP) detectors were designed. The ionization chamber with a silicon nitride entrance window of 100 nm thickness was tested and calibrated with a 252Cf spontaneous fission source. The intrinsic energy resolution for 1.27 MeV/u 63Cu particles is measured to be 450 keV (FWHM). The time resolution was determined with two MCP timing detectors to be 157 ps (FWHM) for 241Am radiation source, implying that the intrinsic time resolution is about 110 ps (FWHM) for a single timing detector. Thermal-neutron-induced fission of 235U was studied at the In-hospital Neutron Irradiator (IHNI). An event-by-event energy loss addback technique was developed based on Geant4 calculation to minimize the correction error. The first results of mass yield distributions from 235U(nth,f) are reported.

Investigation of a prototype double-stack MRPC detector with 20 gas gaps for Time-Of-Flight measurement in PET imaging systems

Resistive Plate Chambers (RPC) are cost-effective gaseous detectors with a very good time and spatial resolution which are extensively used in High Energy Physics and Astroparticle experiments. RPCs have also proposed for Time-Of-Flight (TOF) measurements in Positron Emission Tomography (PET) imaging systems. However, the major limitation of common RPC detectors for PET imaging systems is their low detection efficiency for 511 keV gammas. This paper is focused on the development and investigation of a new RPC detector with improved detection efficiency and time resolution for TOF measurement of 511 keV gamma pairs from electron-positron annihilation. The proposed double-stack Multi-gap RPC (MRPC) detector which is optimized for TOF-PET, consists of 20 gas gaps (with 150 μm width) with 180 μm glass slides (with 24% PbO) as resistive plates in optimum thickness to act as the gamma to electron converter. The proposed detector can work at lower applied voltage with higher count rate capability thanks to the double-stack design and smaller gas gaps width in comparison to common RPCs which were used for TOF-PET applications. The experimental detection efficiency of the proposed MRPC detector for single 511 keV gammas is around 8.3%. At higher applied voltages although the electron multiplication of detector increases, but the detection efficiency saturates, which is related to saturation of dark count rate noise. By using the experimental TOF measurement for electron-positron annihilation gammas, the calculated timing standard deviation of each MRPC detector is 194±40 ps. Moreover, in previous work with the proposed detector it was proved that by using a suitable arrangement of vertical and horizontal readout strips, the pixelated detector can be formed to extract the spatial information of the interaction. According to these results, the proposed prototype detector (which is the first double-stack mode MRPC with 20 gas gaps for TOF-PET application) could be a candidate for TOF measurement system thanks to its suitable time and spatial resolution and also reasonable rate capability. Therefore, it could be an inexpensive alternative for commercial TOF-PET detectors.

Development of a Time-of-Flight Electronics System for Neutron Beam Profiling at CSNS-WNS

A 256-channel time-of-flight (TOF) electronics system has been developed for a beam line facility called "Back-n WNS" in China Spallation Neutron Source (CSNS). This paper shows the structure and performance of electronics system and the test results in CSNS. A 256-channel photomultiplier tube (PMT) is chosen as the detector in this system. In order to acquire the time information from the PMT, an electronics system has been designed. The electronics system mainly includes one front-end board (FEB), four time-to-digital converter (TDC) boards and one clock distribution module (CDM). There are 256 channels on FEB and 64 channels on each TDC board. The FEB is connected to the PMT with high-density connectors and the TDC boards are connected to the FEB through 2m cables. The TDC boards are 6U size so that they can be PCI extensions for Instrumentation (PXI) cards. Data from TDC boards can be transferred to the PXI control card through the backboard. In order to make four TDC boards work synchronously, a CDM outputs four clock signals to TDC boards which are distributed from one clock source. The TDC boards achieve a timing resolution of 3.5ns by test with a signal generator. The TOF measurement system has been used in CSNS.

Behavioral Modeling of Photon Arrival Time for Time-of-Flight Measurement Circuit Simulation

This letter proposes a behavioral model to estimate the statistical photon arrival time for time-of-flight (TOF) measurement circuit simulation. A theoretical model is derived to calculate the photon arrival rate by full consideration of a variety of properties of a TOF measurement system, such as laser source, optics, single-photon avalanche diode detector, target distance, and ambient illumination. For the first time, the newly developed model is implemented in behavioral Verilog-A hardware description language and successfully operated on Cadence Spectre simulator for TOF circuit simulation. It is capable of accurately predicting the statistical performance parameters such as photon arrival time and achievable distance, providing a new candidate tool for the ease of design and simulation of various high-performance TOF measurement circuits.

Study on Time of Flight Measurement for Ultrasonic Tomography

Owing to the distinct advantages, including non-invasive sensing, high safety and low cost, ultrasonic tomography (UT) method is considered as a promising visualization measurement method, in which acquiring high-precision the time of flight (TOF) is crucial for real applications. In this paper, a TOF measurement system is proposed for the UT measurement. The signal analysis is applied for the threshold method to confirm the TOF measurement. The Data acquisition card and the software of Libview are used for the signals acquirement. Experimental studies are implemented to validate the feasibilities of the proposed TOF measurement system, and the experimental results confirm that the TOF measurement system is successful for the TOF measurement.

Laser time-of-flight measurement based on time-delay estimation and fitting correction

We describe a method based on multichannel time-delay estimation with linear fitting correction for laser time-of-flight (TOF) measurement. The laser TOF measurement system is constructed with a laser source, a stop receiver channel, a reference receiver multichannel, an analog to digital converter (ADC) sampling unit, and a digital signal processing unit. Limited by the sampling rate, the precision of laser TOF measurement is restricted no more than the ADC sampling period in conventional methods. As this problem is considered, multichannel correlation time-delay estimation with linear fitting correction is devised. It is shown that the measuring precision is better than 2 ns with multichannel time-delay estimation and not influenced by signal-to-noise ratio. The experimental results demonstrate that the proposed method is effective and stable.

A Synchronous TDMA Ultrasonic TOF Measurement System for Low-Power Wireless Sensor Networks

This paper presents the design and evaluation of an ultrasonic time-of-flight (TOF) measurement system in the context of a smart sensor wireless network. In particular, the ZigBee protocol is used for data transmission and synchronization purposes. Low-cost and low-power restrictions are taken into account in the design. A synchronous measurement scheduling approach is used to minimize the network traffic and, therefore, the power consumption, while avoiding the need of wired connections between the nodes or the use of specific radio link to provide synchronization. A theoretical model that describes the accuracy of the proposed system is derived. This model takes into account both clock drift effects and finite clock resolution of the network nodes. According to the model, the estimation of the TOF is biased due to the clock drifts, and a solution is proposed to compensate this bias. The compensation is based on an accurate estimation that each node performs for its own clock drift. An error analysis of this estimation procedure is also developed, and its effects on the TOF accuracy are presented. A theoretical model of the system that predicts the system performance in terms of TOF accuracies is proposed. An implementation of the TOF measurement system is presented, from which experimental results that validate the theoretical derivations and the effect of the clock drift compensation are obtained. Experimental evaluation of the system also demonstrates that TOF accuracies better than 2 μs are achievable, which will be more than adequate for achieving subcentimetric or even submillimetric precisions in ultrasound-TOF-based distance measurement systems. Even though a particular approach for TOF estimation is considered in this work, most of the derived results are also applicable to other systems involving time synchronous measurements.

Experimental study of ionization of Ar by impact of anions

We describe an experimental apparatus used to study the ionization of gas atoms or molecules in collision with anion projectiles. The setup mainly consists of a time of flight measurement system, a micro-channel plate (MCP) position sensitive detector, and an anode plate MCP detector. These different components of the setup are described in this paper. The single and double ionization processes for Ar under the impact of H anions are studied in the 10–30keV energy range. The results show that the cross section ratios, taken between double and single ionization of Ar for single and double electron loss of H−, become larger and larger with increasing incident energy in the 10–30keV energy range. We also compare our results with the existing H−+Ar data, and find a very interesting phenomenon that the cross section ratios will cross at some energy for the two different electron loss channels.

An Innovative Ultrasonic Time-of-Flight Measurement Method Using Peak Time Sequences of Different Frequencies—Part II: Implementation

This paper researches on the implementation of an ultrasonic time-of-flight (TOF) measuring system by the difference of the peak time sequences (PTSs) of dual frequencies. The process to develop appropriate implementation parameters was demonstrated. Critical characteristics of the transient behavior of the PTS were studied, and their counteracting data processing measures were devised in the process. Obtaining the PTS by averaging repeated test data and the linear regression on the PTS was found to be effective in uncovering the actual TOF of the first wavefront with high precision. A PC-based test bench was built to test the characteristics and to verify the performance of the new TOF measurement system. In our TOF measurement over the distance of 145 cm, a standard deviation (STD) of 0.0113 of a period was achieved by a nominal driving wave period of 25.6 μs (39 kHz) and a frequency difference factor of 0.0048. When applied to a distance measurement, the worst STD of 0.097 mm was achieved with a relative distance ranging up to 1450 mm, given the nominal driving wavelength of 8.6 mm. This new dual-frequency PTS-based TOF measurement system can be economically embedded in a microcontroller, together with a field-programmable gate array, and some simple transistors that are suitable for positioning mobile units indoors or in small open-field environments.

Proposal of generalized vernier effect and its practical advantage for RF time-of-flight ranging between sensor nodes in wireless sensor networks

Accurate ranging technique is indispensable for node localization in wireless sensor networks (WSNs), and there are various ranging techniques/systems using physical characteristics of RF signals. The RF time-of-flight (ToF) ranging technique in a short distance is still difficult to implement since both a high precision clock system and complex signal processing are required to exactly measure RF ToF. This paper presents an improvement of time resolution based on the generalized vernier effect (GVE) by which it is possible to accurately measure short-range RF ToF using low operating clocks of several megahertz. The GVE-based RF ToF measurement methodology is certified through experiments to measure a singular sensing pattern with respect to RF round-trip time using a prototype of the synch-free RF ToF measurement system, which is a practical RF ToF ranging system for application to the localization of WSNs.

A setup for probing ion–molecule collision dynamics

We describe a setup for studies of dissociation dynamics of multiply charged molecules formed due to highly charged ion impact. The setup consists of a multihit, position-sensitive, time of flight measurement system along with an electrostatic analyzer with offset detector. Brief description of different components of the setup and electronics for multihit data acquisition is presented in this paper. Coulomb explosion of multiply ionized N 2 and charge exchange studies on Ar with highly charged projectile ion is carried out to test the performance of the spectrometer and its multifold coincidence capabilities.