Time Of Flight Method Research Articles

Marble Ageing Characterization by Acoustic Waves

In cultural heritage, statue marble characterization by acoustic waves is a well-known non-destructive method. Such investigations through the statues by time of flight method (TOF) point out sound speeds decrease with ageing. However for outdoor stored statues as the ones in the gardens of Chateau de Versailles, ageing affects mainly the surface of the Carrara marble. The present paper proposes an experimental study of the marble acoustic properties variations during accelerated laboratory ageing.The surface degradation of the marble is reproduced in laboratory for 29mm thick marble samples by using heating/cooling thermal cycles on one face of a marble plate. Acoustic waves are generated by 1 MHz central frequency contact transducers excited by a voltage pulse placed on both sides of the plate. During the ageing and by using ad hoc transducers, the marble samples are characterized in transmission, along their volume by shear, compressional TOF measurements and along their surface by Rayleigh waves measurements. For Rayleigh waves, both TOF by transducers and laser vibrometry methods are used to detect the Rayleigh wave. The transmission measurements point out a deep decrease of the waves speeds in conjunction with a dramatic decrease of the maximum frequency transmitted. The marble acts as a low pass filter whose characteristic frequency cut decreases with ageing. This pattern occurs also for the Rayleigh wave surface measurements. The speed change in conjunction with the bandwidth translation is shown to be correlated to the material de-structuration during ageing. With a similar behavior but reversed in time, the same king of phenomena have been observed trough sol-gel materials during their structuration from liquid to solid state (Martinez, L. et all (2004). “Chirp-Z analysis for sol–gel transition monitoring”. Ultrasonics, 42(1), 507-510.). A model is proposed to interpret the acoustical measurements

Analysis of charge transport in high-mobility diketopyrrolopyrole polymers by space charge limited current and time of flight methods

The hole mobility of the widely studied diketopyrrolopyrole-based polymers (PDPPDTSE) was examined using space charge limited current (SCLC) and time of flight (TOF) methods. The mobility of the hole-only device based on PDPPDTSE was found to be dependent upon the e-field over the range of 10−3 to 10−2 cm2 V−1 s−1 with nearly identical Poole–Frenkel coefficients. In addition, we found that the mobility strongly depended on the thickness of the PDPPDTSE. By analyzing the temperature dependence of transport characteristics, we argued that the charge transport in this polymer was greatly influenced by trap distribution at the electrode/semiconductor interface.

Analysis of processes in Li-ion batteries by time-of-flight neutron diffraction

Ex-situ and in-situ neutron diffraction experiments were performed at HRFD time-of-flight (TOF) diffractometer (IBR-2 long-pulsed reactor, JINR) to characterize the entire battery system based on LiFePO4 and V-added LiFePO4 electrodes during electrochemical cycling and to find additional information about crystal structure of electrodes. Another purpose of this work was checking possibilities for in-situ experiments with real Li-ion batteries at the IBR-2 pulsed reactor. An important advantage of TOF method is the possibility to work at the fixed geometry of the experiment, which allows selecting the optimal battery orientation relative to the directions of the incident and scattered neutron beams and, thus, to minimize the difficulties associated with complex internal structure of the battery. It was shown that charge/discharge process of Li-based real Li-ion battery can be effectively studied by TOF technique at the IBR-2 pulsed reactor. Three full charge/discharge cycles were realized at room temperature (~170C) with slow rate. The step-like appearance of several LiCn phases was observed and the volume fractions of LiFePO4 and FePO4 structural phases at different states of charge were determined. The analysis of changes in cathode material microstructure when doped with vanadium showed a significant increase in the density of defects, which correlates with better electrochemical properties of V-added LiFePO4 compared to pure LiFePO4.

Neutron-Physical Characteristics of a Neutron Source for the Production of Radioactive Isotopes Based on the Interaction of Electrons with Liquid Gallium

The nuclear-physical characteristics obtained for a gallium target in a series of experiments using the timeof-flight method, the method of threshold indicators and a spectrometer based on a 3 He proportional counter on the IREN setup (JINR, Dubna) are presented. The absolute values of the energy spectra of leakage neutrons in the energy range from 10 keV to 15 MeV were measured. The activation method was used to measure the neutron flux density on the surface of a gallium target: (2.882 ± 0.098)·10 8 sec ‐1 ·cm ‐2 . The integral yield of neutrons obtained from the gallium target on the basis of these data was 1.54·10 14 sec ‐1 with average current 4 mA. The time dependence of the activation level of the gallium target was measured. It was shown as a result of the analysis that the background level is reached on the surface of the irradiated gallium target in 5 days. The results of an experimental validation of a photoneutron source based on liquid gallium with no fissile materials, which is characterized by sufficient neutron yield for the production of radioactive isotopes for medical purposes, are present in this article. The method is based on a two-step process in which the reaction (γ, n) serves as the generator of the neutron flux, and the isotopes are produced by the neutron capture reaction (n, γ) or the neutron capture reaction (n, p) with the emission of a proton. For this reason, the database of neutron-physical constants for calculating the optimal configuration of the irradiation setup is expanded by including in it the cross sections of reactions induced by neutrons, as a result of which additional uncertainties in the computed quantities arise. Measurement of the Yield and the Angular and Energy Distributions of the Neutrons Generated in Gallium by 33.58 MeV Electrons. The IREN setup (Joint Institute for Nuclear Research, JINR, Dubna), operating in the pulsed regime with pulse repetition frequency 25 Hz, was used as the electron accelerator [1]. The average energy of the electrons incident on the gallium target was measured in a separate experiment and was equal to 33.58 MeV. The pulse width was 0.1 μsec and the current in a pulse was 1 A. The neutron flux monitor located in the experimental room showed high stability of the electron current. For this reason, the experimental data were processed assuming the intensity of the neutron source to be constant.

Quantitative analysis of temperature dependent acoustic trapping characteristics by using concentric annular type dual element ultrasonic transducer

This paper presents the temperature dependence of lateral acoustic trapping capability by probing the speed of sound in individual lipid droplets at a given temperature of water and measuring its corresponding displacement, a value for quantitatively evaluating a spring-like behavior of the acoustic trap with certain strength. A 20/40MHz dual element LiNbO3 ultrasonic transducer is fabricated to simultaneously perform both transverse trapping and sound speed measurement for each droplet over a discrete temperature range from 20°C to 30°C. Time of flight method is employed for pulse tracking that determines the arrival time of an echo reflected back from either a trapped droplet or a mylar film.The estimated speeds of sound in water and droplets are 1484.8m/s and 1431.6m/s at 20°C, while 1506.0m/s and 1400.6m/s at 30°C, respectively. As the temperature rises, the sound speed in droplets decreases at an average rate of 3.1m/s/°C, and the speed in water increases at 2.1m/s/°C. The average displacement varies from 150.0μm to 179.0μm with an increasing rate of 2.9μm/°C, and its standard deviation is obtained between 1.0μm and 2.0μm over the same temperature range. Reduced sound speed as a function of rising temperature results in increased displacement, indicating that the trapping strength is adjustable by regulating ambient temperature in water as well as by changing transducer excitation parameters. Therefore, the results suggest that the temperature dependence of this trapping technique can be exploited for developing a remote manipulation tool of micron-sized particles in a thermally fluctuating environment. It is also shown that any deviated trapping strength caused by thermal disturbance near the trap can be restored to its desired level by compensating either temperature difference or trapping system condition.

Computation of Wave Propagation in Damped Specimen for Damage Detection

Aim of a structural health monitoring system must be to collect sufficient information about the damage for appropriate remedial measures to be taken to ensure safety. The preliminary step in the process of damage assessment is locating the damage .One of the challenges faced by the structural health monitoring system is monitoring in-flight damages. Localization of in-flight damages or sudden impacts can be achieved by monitoring the acoustic emissions in real time mode. In this paper, an approach based on the employment of Piezo-electric transducer rosettes to locate the acoustic emission source in an aluminum plate is presented. Using the strain gage rosette concepts adapted for piezoelectric transducers, the wave strain principal angles are determined. When two rosettes are used, the intersection of the principal wave strain directions detected by the rosettes gives the wave source location. The method does not require the knowledge of wave velocity in the medium in contrast to the time of flight based location. Hence, this technique can be used in anisotropic or complex structures where the source localization using the conventional time of flight method is difficult. The principal strain angle using the voltage response of the transducers and the rosette principles are obtained and the co-ordinates of the wave source location are calculated using the co-ordinates of the centroids of the rosettes in MATLAB.According to the tests, the rosette piezo-transducer outperforms the single piezo elements to a degree justifying its complexity. The rosette piezo transducer provides more damage related information compared to single elements and hence the performance of the damage detection system can be significantly improved if rosettes are used.

Cross Section Measurements of the Radioactive 107Pd and Stable 105,108Pd Nuclei at J-PARC/MLF/ANNRI

The measurements of the neutron-capture cross sections were performed for the radioactive 107Pd and stable 105,108Pd nuclei by the time-of flight method using an apparatus called “Accurate Neutron–Nucleus Reaction measurement Instrument (ANNRI)” installed at the neutron Beam Line No.4 of the Materials and Life science experimental Facility (MLF) in the J-PARC. The neutron-capture cross sections of 107Pd and 105,108Pd have been measured in the low energy region from the thermal to a few hundreds eV. From the measurements, new information was obtained for some resonances of these Pd nuclei.

Digital discrimination of neutron and γ ray using an organic scintillation detector based on wavelet transform modulus maximum

A novel algorithm for the discrimination of neutron and γ-ray events with wavelet transform modulus maximum (WTMM) in an organic scintillation has been investigated. Voltage pulses arising from a BC501A organic liquid scintillation detector in a mixed radiation field have been recorded with a fast digital sampling oscilloscope. The WTMM method using frequency-domain features exhibits a strong insensitivity to noise and can be used to discriminate neutron and γ-ray events based on their different asymptotic decay trend between the positive modulus maximum curve and the negative modulus maximum curve in the scale-space plane. This technique has been verified by the corresponding mixed-field data assessed by the time-of-flight (TOF) method and the charge comparison (CC) method. It is shown that the characterization of neutron and γ ray achieved by the discrimination method based on WTMM is consistent with that afforded by the TOF method and better than the CC method. Moreover, the WTMM method itself has presented its ability to eliminate the noise without any pretreatment to the pulses.

Application Study on Multiple Acoustic Paths Intersection in Temperature Field Measurement

Acoustic Pyrometry enables non-intrusive, accurate, reliable gas temperature measurements which can be used for controlling operations on real-time basis, therefore, it particularly applies to hot zones and extremely harsh environments. In the application study on multiple acoustic paths intersection in temperature field measurement, two key techniques that time of flight (TOF) of acoustic waves measurement and temperature field reconstruction were involved. This paper introduces the development of Acoustic Pyrometry, and then focus on two key techniques. The cross-correlation algorithm to calculate the TOF and least-square method for temperature field reconstruction are presented. The advantages and limitations of these techniques are also discussed. Several emerging questions are proposed.

Measurement of neutron energy spectrum from 241 Am-B source using CR-39 detectors and an in-house image analysis program (autoTRAK_n)

An attempt has been made in the present work to estimate the neutron spectrum of a standard 241 Am-B source using CR-39 solid polymeric track detector and an in-house image analysis program autoTRAK_n. The program works on the principle of greyscale variations in and around the recoil tracks and calculates the track parameters such as diameter, major, minor axes and estimates three dimensional parameters like recoil track depth and angular incidence. It is also capable of counting overlapping tracks without any segregation procedure. In the present study, the standard 241 Am-B neutron spectrum generated from the recoil track parameters with the autoTRAK_n program is compared with the reported values measured using the time of flight method and found to be matching well, mainly at the characteristic peak. The total neutron fluence and dose equivalents are also determined with the program and are compared with the standard source measurements. The results obtained from autoTRAK_n are found to be in close agreement with the standard measurements with less than 5% error for both the parameters. Hence, this methodology can be used as a backup technique for neutron spectrum measurements along with other techniques considering its low cost, small size, easy irradiation, and processing.

Optimization of Lower Limbs MR for Angiography with Contrast Injection in 1.5 Tasla by Time of Flight Method

During different studies on 1.5 Tasla equipments it was possible to obtain proper images with different values for different parts of limb. To date no research of such kind has been done in Iran and angiography of lower limbs is not done at present. In this study, it was tried to proper images of lower limbs considering the capabilities of designed protocol system.1.5 Tasla MRI equipment with optimized parameters for different positions calculated on the volunteers, patients and phantom was used. SNR and CNR images were compared, and categorized by radiologist based on diagnostic values. First stage of recovery current, a lower, mobile pre saturated pulses, NSA=1, matrix size 128 to 180 at direct phase and 256 direct frequency were selected. The qualitative value of the images 3 at pelvis area; 3 at femoral and knee areas; and 4 for knee was obtained. Total time required for imaging of lower limb was 45 minutes. This techniques is useful particularly for the patients who can not go under conventional angiography. The value of the MR images using contrast drug is higher than the images obtained by this method, however this method is cheaper.

Development of nanoimprinted InP QDs decorated polyaniline solar cell with conversion efficiency 3%

Organic–inorganic hybrid materials received considerable attention due to promising industrial applications. The originality of novel chemical recipes, allowing incorporation of well-defined nanoparticle structures into complex hybrid architectures, opens new possibilities for multidisciplinary fields and in particular in optoelectronic devices. The rate of non-radiative recombination and energy transfer through a hybrid inorganic/organic nanocomposite is mainly governing the ability of charge transfer from semiconductor quantum dots to conjugated polymers. Herein, we report that the electron–hole non-radiative recombination in polymer can be constricted by funneling the diffusion of exciton by engineering a proper morphology of a hybrid nanostructure. InP quantum dots have been selected due to their efficient exciton generation and polyaniline as a conjugated polymer for its potency to suppress non-radiative recombination by restraining exciton diffusion. The hole transfer was monitored via bi-exponential kinetic model and time of flight method. The conversion efficiency of the prepared films increased from 0.23% to 3.1% when the thickness is increased from 14nm to 157nm.

Demonstration of determination of electron and hole drift-mobilities in organic thin films by means of impedance spectroscopy measurements

The electron and hole drift-mobilities of tris(8-hydroxy-quinolinato) aluminium (Alq3) thin films have been determined using impedance spectroscopy (IS) measurements. The theoretical basis of drift-mobility measurement with IS rests on a theory for single-injection space-charge limited current. The electron drift-mobilities in Alq3 which measured from the frequency dependence of both capacitance and conductance had the same electric-field dependence and were identical to those measured by a time-of-flight (TOF) transient photocurrent technique. To estimate the hole drift-mobility in Alq3, a 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl thin film was inserted as an injection layer to reduce the hole injection barrier between an injection electrode and the Alq3 thin film. The hole drift-mobilities of Alq3 thin films measured with IS were identical to those measured by the TOF method. These results are essential for clarifying the mechanism of the carrier transport of organic light emitting diodes (OLEDs) with the aim of improving OLED performance.

Neutron Dosimetry in Quasi-Monoenergetic Fields of 244 and 387 MeV

This paper describes the results of neutron spectrometry and dose measurements using a Bonner Sphere Spectrometer (BSS) at the ring cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University, Japan. Quasi-monoenergetic neutron fields were generated using the 7Li (p,n)7Be reaction and 246 and 389 MeV protons. Neutrons produced at 0° and 30° emission angles were extracted into a time-of-flight (TOF) tunnel, and the energy spectra were measured at a distance of 35 m from the target. To deduce the corresponding neutron spectra from thermal to the nominal maximum energy, the BSS data were unfolded using the MSANDB code and response functions were calculated by Monte Carlo (MC) methods. These spectra are compared to spectral measurements using NE213 organic liquid scintillators applying the TOF method. The results are discussed in terms of ambient dose equivalent H* (10) and compared with the readings of other instruments operated during the experiment.

Surface Photocatalysis-TPD Spectrometer for Photochemical Kinetics

A surface photocatalysis-TPD apparatus devoted to studying kinetics and mechanism of photocatalytic processes with various signal crystal surfaces has been constructed. Extremely high vacuum (∼0.2 nPa) in the ionization region is obtained by using multiple ultrahigh vacuum pumps. Compared with similar instruments built previously by others, the H2, CH4 background in the ionization region can be reduced by about two orders of magnitude, and other residual gases in the ionization region can be reduced by about an order of magnitude. Therefore, the signal-to-noise ratio for the temperature programmed desorption (TPD) and time of flight (TOF) spectra is substantially enhanced, making experimental studies of photocatalytic processes on surfaces much easier. In this work, we describe the new apparatus in detail and present some preliminary studies on the photo-induced oxygen vacancy defects on TiO2(110) at 266 nm by using the TPD and TOF methods. Preliminary results suggest that the apparatus is a powerful tool for studying kinetics and mechanism of photochemical processes.

Bipolar charge transport property of N,N′-dicarbazolyl-1,4-dimethene-benzene: A study of the short range order model

Short range order model is commonly used to explain the charge transport property of disordered organic semiconductors. However, its validity is not yet studied. In this paper, the hole and electron mobilities of a bipolar material, N,N′-dicarbazolyl-1,4-dimethene-benzene (DCB), were measured through time of flight method. The hole and electron mobilities of DCB based on the crystalline structure were calculated. In order to investigate the short range order model, the ratios of charge mobilities at zero electric field of holes to electrons were calculated. The results showed that this model cannot fully explain our case. The reason was discussed in detail, and a correction method was proposed. We showed that using the short range order model without preconditions to explain the charge transport property of amorphous materials may lead to deviations, which is often neglected in the past.

Development of gas cluster ion beam irradiation system with an orthogonal acceleration TOF instrument

Surface damage induced on biomolecules with gas cluster ion beam (GCIB) irradiation is significantly lower than with atomic or small cluster ion beams, and for this reason, surface analysis techniques such as secondary ion mass spectrometry (SIMS) have become one of the most important applications of GCIB, particularly for microscale chemical imaging of biomolecular species. Because of the low duty‐cycle in time‐of‐flight (TOF)‐SIMS, only less than 0.1 % of the incident ion beam is used for analysis, meaning that analysis with high spatial resolution can practically be extremely lengthy. The duty cycle can be significantly improved with the orthogonal acceleration (oa) TOF method because with this method secondary ion mass spectra can be measured at high mass resolution without requiring a pulsed primary ion beam. In this study, we developed a gas cluster ion irradiation system mounted on an oa‐TOF instrument and investigated the sputtering yield and secondary ion yield of arginine. Copyright © 2012 John Wiley & Sons, Ltd.

High-Accuracy Reference-Free Ultrasonic Location Estimation

This paper presents a novel reference-free ultrasonic indoor location system. Unlike most previous proposals, the mobile device (MD) determines its own position based only on ultrasonic signals received at a compact sensor array and sent by a fixed independent beacon. No radio frequency or wired timing reference signal is used. Furthermore, the system is privacy aware and one way in that the receive-only MD determines its own position based on ultrasonic signals received from fixed transmit-only beacons. The MD uses a novel hybrid angle of arrival (AoA)-time of flight (ToF) with timing lock algorithm to determine its location relative to the beacons with high accuracy. The algorithm utilizes an AoA-based location method to obtain an initial estimate of its own location. Based on this, it estimates the timing offsets (TOs) between the MD clock and the beacon transmissions. The average TO and the known periodicities of the beacon signals are then used to obtain a second more accurate MD location estimate via a ToF method. The system utilizes wideband spread spectrum ultrasonic signaling in order to achieve a high update rate and robustness to noise and reverberation. A prototype system was constructed, and the algorithm was implemented in software. The experimental results show that the method provides 3-D accuracy better than 9.5 cm in 99% of cases, an 80% accuracy improvement over the conventional AoA-only method.

Results for the response function determination of the Compact Neutron Spectrometer

The Compact Neutron Spectrometer (CNS) is a Joint European Torus (JET) Enhancement Project, designed for fusion diagnostics in different plasma scenarios. The CNS is based on a liquid scintillator (BC501A) which allows good discrimination between neutron and gamma radiation. Neutron spectrometry with a BC501A spectrometer requires the use of a reliable, fully characterized detector. The determination of the response matrix was carried out at the Ion Accelerator Facility (PIAF) of the Physikalisch-Technische Bundesanstalt (PTB). This facility provides several monoenergetic beams (2.5, 8, 10, 12 and 14 MeV) and a white field (Emax ∼ 17 MeV), which allows for a full characterization of the spectrometer in the region of interest (from ∼ 1.5 MeV to ∼ 17 MeV). The energy of the incoming neutrons was determined by the time of flight method (TOF), with time resolution in the order of 1 ns. To check the response matrix, the measured pulse height spectra were unfolded with the code MAXED and the resulting energy distributions were compared with those obtained from TOF. The CNS project required modification of the PTB BC501A spectrometer design, to replace an analog data acquisition system (NIM modules) with a digital system developed by the Ente per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA). Results for the new digital system were evaluated using new software developed specifically for this project.

Measurement of Temperature of Atomic Cloud Using Time-of-Flight Technique

We present a discussion on the time-of-flight (TOF) technique for measuring temperature of cold atom clouds, with specific focus on fountain experiments. In these experiments, there exists a possibility of losing substantial number of atoms owing to the interaction of the cloud with the wall of the cavity, in case the dimension of the former exceeds the latter. Hence, we propose to include the contribution of the location and geometry of the cavity in the TOF method which otherwise, generally relies on the cloud shape and the geometry of the probe beams only. A theoretical analysis is presented and it is substantiated with experimental results for cloud temperatures of <10 μK and toss heights of up to 72 cm.