Showing papers on "Time of flight published in 2013"

DELICIOUS III: A multipurpose double imaging particle coincidence spectrometer for gas phase vacuum ultraviolet photodynamics studies

Abstract: We present a versatile double imaging particle coincidence spectrometer operating in fully continuous mode, named DELICIOUS III, which combines a velocity map imaging device and a modified Wiley-McLaren time of flight momentum imaging analyzer for photoelectrons and photoions, respectively. The spectrometer is installed in a permanent endstation on the DESIRS vacuum ultraviolet (VUV) beamline at the French National Synchrotron Radiation Facility SOLEIL, and is dedicated to gas phase VUV spectroscopy, photoionization, and molecular dynamics studies. DELICIOUS III is capable of recording mass-selected threshold photoelectron photoion coincidence spectra with a sub-meV resolution, and the addition of a magnifying lens inside the electron drift tube provides a sizeable improvement of the electron threshold/ion mass resolution compromise. In fast electron mode the ultimate kinetic energy resolution has been measured at ΔE/E = 4%. The ion spectrometer offers a mass resolution—full separation of adjacent masses—of 250 amu for moderate extraction fields and the addition of an electrostatic lens in the second acceleration region allows measuring the full 3D velocity vector for a given mass with an ultimate energy resolution of ΔE/E = 15%, without sacrificing the mass resolution. Hence, photoelectron images are correlated both to the mass and to the ion kinetic energy and recoil direction, to access the electron spectroscopy of size-selected species, to study the photodissociation processes of state-selected cations in detail, or to measure in certain cases photoelectron angular distributions in the ion recoil frame. The performances of DELICIOUS III are explored through several examples including the photoionization of N2, NO, and CF3.

A prototype of a new inductively coupled plasma time-of-flight mass spectrometer providing temporally resolved, multi-element detection of short signals generated by single particles and droplets

Abstract: A prototype inductively coupled plasma time-of-flight mass spectrometer (ICPTOFMS) for time resolved measurements of transient signals in the microsecond regime is described in this work. Analytical figures of merit for the prototype are given for both liquid nebulization and single droplet introduction and are compared to a conventional quadrupole-based ICPMS using the same ICP source and vacuum interface. Quasi-simultaneous detection at a time resolution of 33 μs of the prototype ICPTOFMS allows multi-isotope monitoring of short signals (200–500 μs duration) generated from individual droplets and particles. The capabilities of the instrument for the analysis of single nanoparticles are studied using microdroplets consisting of a multi-element standard solution and containing 114 nm Au particles. The detection efficiencies for Ag and Au, calculated from the response of individual droplets and particles, are similar to those of the quadrupole-based instrument and amount to 1.3 × 10−6 ions per atom and 3.1 × 10−6 ions per atom, respectively. The sizes of the smallest detectable Ag, Au and U metallic nanoparticles are estimated to be 46 nm, 32 nm and 22 nm, respectively. Furthermore, time shifts of the signals of different elements within single droplets were observed. These new results demonstrate the advantage of the temporal resolution of the instrument for studying processes taking place in the plasma on the μs-time scale.

Time of flight positron emission tomography towards 100ps resolution with L(Y)SO: An experimental and theoretical analysis

Abstract: Scintillation crystals have a wide range of applications in detectors for high energy and medical physics. They are recquired to have not only good energy resolution, but also excellent time resolution. In medical applications, L(Y)SO crystals are commonly used for time of flight positron emission tomography (TOF-PET). This study aims at determining the experimental and theoretical limits of timing using L(Y)SO based scintillators coupled to silicon photomultipliers (SiPMs). Measurements are based on the time-over-threshold method in a coincidence setup utilizing the ultra-fast amplifier-discriminator NINO and a fast oscilloscope. Using a 2 × 2 × 3 mm3 LSO:Ce codoped 0.4% Ca crystal coupled to a commercially available SiPM (Hamamatsu S10931-050P MPPC), we achieve a coincidence time resolution (CTR) of 108±5ps FWHM measured at E=511keV. We determine the influence of the data acquisition system to 27±2ps FWHM and thus negligible as compared to the CTR. This shows that L(Y)SO scintillators coupled to SiPM photodetectors are capable of achieving very good time resolution close to the desired 100ps FWHM for TOF-PET systems. To fully understand the measured values, we developed a simulation tool in MATLAB that incorporates the timing properties of the photodetector, the scintillation properties of the crystal and the light transfer within the crystal simulated by SLITRANI. The simulations are compared with measured data in order to determine their predictive power. Finally we use this model to discuss the influence of several important parameters on the time resolution like scintillation rise- and fall time and light yield, as well as single photon time resolution (SPTR) and the detection efficiency of the SiPM. In addition we find the influence of photon travel time spread in the crystal not negligible on the CTR, even for the used 2 × 2 × 3 mm3 geometry.

Kinetics of ion and prompt electron emission from laser-produced plasma

Abstract: We investigated ion emission dynamics of laser-produced plasma from several elements, comprised of metals and non-metals (C, Al, Si, Cu, Mo, Ta, W), under vacuum conditions using a Faraday cup. The estimated ion flux for various targets studied showed a decreasing tendency with increasing atomic mass. For metals, the ion flux is found to be a function of sublimation energy. A comparison of temporal ion profiles of various materials showed only high-Z elements exhibited multiple structures in the ion time of flight profile indicated by the observation of higher peak kinetic energies, which were absent for low-Z element targets. The slower ions were seen regardless of the atomic number of target material propagated with a kinetic energy of 1–5 keV, while the fast ions observed in high-Z materials possessed significantly higher energies. A systematic study of plasma properties employing fast photography, time, and space resolved optical emission spectroscopy, and electron analysis showed that there existed different mechanisms for generating ions in laser ablation plumes. The origin of high kinetic energy ions is related to prompt electron emission from high-Z targets.

The 3-D plasma distribution function analyzers with time-of-flight mass discrimination for Cluster, FAST, and Equator-S

Abstract: A similar time-of-flight plasma analyzer system will be flown as CODIF (COmposition and Dlstribution Function analyzer) on the four Cluster spacecraft, as ESIC (Equator-S Ion Composition instrument) on Equator-S, and as TEAMS (Time-of-flight Energy Angle Mass Spectrograph) on FAST. These instruments will for the first time allow the 3-dimensional distribution functions of individual ion species to be determined within 1/2 or 1 spin period. This will be crucial for the study of selective energization processes in various regions of the magnetosphere. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360° in polar angle. For Cluster and Equator-S this range is subdivided into two halves with geometric factors different by a factor of 100 in order to cope with the wide dynamic range of fluxes in the magnetosphere. For FAST the time resolution is increased by a factor of two to focus on fast auroral phenomena by using both halves simultaneously. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated in calibration runs that the instruments can easily separate H + , He 2+ , He + , O + and for energies after post-acceleration of 3 20 keV even O 2 + molecules. On board discrimination, accumulation, and moment computation allow efficient retrieval of the data stream.

Note: a novel dual-channel time-of-flight mass spectrometer for photoelectron imaging spectroscopy.

Abstract: A novel dual-channel time-of-flight mass spectrometer (D-TOFMS) has been designed to select anions in the photoelectron imaging measurements. In this instrument, the radiation laser can be triggered precisely to overlap with the selected ion cloud at the first-order space focusing plane. Compared with that of the conventional single channel TOFMS, the in situ mass selection performance of D-TOFMS is significantly improved. Preliminary experiment results are presented for the mass-selected photodetachment spectrum of F− to demonstrate the capability of the instrument.

Picosecond resolution on relativistic heavy ions' time-of-flight measurement

Abstract: We developed a time-of-flight measurement system for relativistic heavy ions with a requested resolution of 40 ps Full Width Half Maximum. Such a resolution is mandatory to assign the correct mass number to every fission fragment, identified using the B ρ - ToF - Δ E method with the recoil spectrometer designed for the SOFIA experiment—which hold very recently at GSI. To achieve such a performance, fast plastic scintillators read-out by dedicated photomultiplier tubes were chosen among other possible options. We have led several test-measurements from 2009 to 2011, in order to investigate: the effect of the addition of a quenching molecule in the scintillator's matrix, the influence of the detector's size and the impact of the photomultiplier tube. The contribution of the dedicated electronics is also characterized. Time-of-flight measurements were performed realized with electron pulses and relativistic heavy ions, respectively provided by the LASER driven electron–accelerator (ELSA) at CEA–DAM Ile-de-France and by the SIS18/FRS facility at GSI. The reported results exhibit a time resolution better than 20 ps Full Width Half Maximum reached with the last prototype at GSI with an Uranium beam. These results confirm that the SOFIA experiment should enable the measurement of the relativistic fission fragments' time-of-flight with the requested resolution.

Organic particle types by single-particle measurements using a time-of-flight aerosol mass spectrometer coupled with a light scattering module

Abstract: . Chemical and physical properties of individual ambient aerosol particles can vary greatly, so measuring the chemical composition at the single-particle level is essential for understanding atmospheric sources and transformations. Here we describe 46 days of single-particle measurements of atmospheric particles using a time-of-flight aerosol mass spectrometer coupled with a light scattering module (LS-ToF-AMS). The light scattering module optically detects particles larger than 180 nm vacuum aerodynamic diameter (130 nm geometric diameter) before they arrive at the chemical mass spectrometer and then triggers the saving of single-particle mass spectra. 271 641 particles were detected and sampled during 237 h of sampling in single-particle mode. By comparing timing of the predicted chemical ion signals from the light scattering measurement with the measured chemical ion signals by the mass spectrometer for each particle, particle types were classified and their number fractions determined as follows: prompt vaporization (46%), delayed vaporization (6%), and null (48%), where null was operationally defined as less than 6 ions per particle. Prompt and delayed vaporization particles with sufficient chemical information (i.e., more than 40 ions per particle) were clustered based on similarity of organic mass spectra (using k-means algorithm) to result in three major clusters: highly oxidized particles (dominated by m/z 44), relatively less oxidized particles (dominated by m/z 43), and particles associated with fresh urban emissions. Each of the three organic clusters had limited chemical properties of other clusters, suggesting that all of the sampled organic particle types were internally mixed to some degree; however, the internal mixing was never uniform and distinct particle types existed throughout the study. Furthermore, the single-particle mass spectra and time series of these clusters agreed well with mass-based components identified (using factor analysis) from simultaneous ensemble-averaged measurements, supporting the connection between ensemble-based factors and atmospheric particle sources and processes. Measurements in this study illustrate that LS-ToF-AMS provides unique information about organic particle types by number as well as mass.

Neutrino mass sensitivity by MAC-E-Filter based time-of-flight spectroscopy with the example of KATRIN

Abstract: The KArlsruhe TRItium Neutrino (KATRIN) experiment aims at a measurement of the neutrino mass with a 90% confidence limit (CL) sensitivity of 0.2 eV/c2 by measuring the endpoint region of the tritium β decay spectrum from a windowless gaseous molecular tritium source using an integrating spectrometer of the magnetic adiabatic collimation with an electrostatic filter (MAC-E-Filter) type. We discuss the idea of using the MAC-E-Filter in a time-of-flight mode (MAC-E-TOF) in which the neutrino mass is determined by a measurement of the electron TOF spectrum that depends on the neutrino mass. MAC-E-TOF spectroscopy here is a very sensitive method since the β-electrons are slowed down to distinguishable velocities by the MAC-E-Filter. Their velocity depends strongly on their surplus energy above the electric retarding potential. Using MAC-E-TOF, a statistical sensitivity gain is expected. Because a small number of retarding-potential settings is sufficient for a complete measurement, in contrast to about 40 different retarding potentials used in the standard MAC-E-Filter mode, there is a gain in measurement time and hence statistical power. The improvement of the statistical uncertainty of the squared neutrino mass has been determined by Monte Carlo simulation to be a factor 5 for an ideal case neglecting background and timing uncertainty. Additionally, two scenarios to determine the TOF of the β-electrons are discussed, which use the KATRIN detector for creating the stop signal and different methods for obtaining a start signal. These comprise the hypothetical case of an 'electron tagger' which detects passing electrons with minimal interference and the more realistic case of 'gated filtering', where the electron flux is periodically cut off by pulsing the pre-spectrometer potential.

Time-of-flight electron spectrometer for a broad range of kinetic energies.

Abstract: A newly constructed time-of-flight electron spectrometer of the magnetic bottle type is characterized for electron detection in a broad range of kinetic energies. The instrument is designed to measure the energy spectra of electrons generated from liquids excited by strong laser fields and photons in the range of extreme ultra violet and soft X-rays. Argon inner shell electrons were recorded to calibrate the spectrometer and investigate its characteristics, such as energy resolution and collection efficiency. Its energy resolution ΔE/E of 1.6% allows resolving the Ar 2p spin orbit structure at kinetic energies higher than 100 eV. The collection efficiency is determined and compared to that of the spectrometer in its field-free configuration.

Emission features of femtosecond laser ablated carbon plasma in ambient helium

Abstract: We investigated the optical emission features of plasmas produced by 800 nm, 40 fs ultrafast laser pulses on a carbon target in the presence of ambient helium or nitrogen gases at varied pressures. Fast photography employing intensified charge coupled device, optical emission spectroscopy, and temporally spatially resolved optical time of flight emission spectroscopy were used as diagnostic tools. Spatio-temporal contours of excited neutral, ionic, as well as molecular carbon species in the plume were obtained using time of flight emission spectroscopy. These contours provided detailed account of molecular species evolution and expansion dynamics and indicate that three-body recombination is a major mechanism for carbon dimers generation in ultrafast laser ablation plumes in the presence of ambient gas. A systematic comparison of the emission features from ns and fs laser ablation carbon plumes as well as their expansion in ambient helium is also given. C2 vibrational temperatures were estimated during carbon plasma expansion with lower values in ambient helium compared to nitrogen and showed decreasing values with respect to space and ambient gas pressure.

Dissociative electron attachment to acetaldehyde, CH3CHO. A laboratory study using the velocity map imaging technique.

Abstract: A detailed experimental investigation of the dissociative electron attachment (DEA) process to acetaldehyde, CH3CHO is presented. To investigate this process we use a time of flight spectrometer coupled with the velocity slice imaging technique. DEA in CH3CHO is found to lead to the formation of CH3−, O−, OH−, C2H−, C2HO− and CH3CO− anionic products produced through scattering resonances in the electron energy range of 6 to 13 eV. Of these product ions only O− is formed with any measurable kinetic energy distribution indicating a two-body dissociation process. CH3CO−, although formed with very low kinetic energy, shows anisotropy in the velocity slice image, indicating ejection of the H atom in the 180° direction with respect to the electron beam. The low kinetic energy distributions and absence of any anisotropy in the angular distributions of the other product ions indicate that they are formed through multiple fragmentation of the transient molecular negative ion. The angular distribution of O− is analysed in terms of the various partial waves.

Probing the orientation of electrostatically immobilized cytochrome C by time of flight secondary ion mass spectrometry and sum frequency generation spectroscopy

Abstract: By taking advantage of the electron pathway through the heme group in cytochrome c (CytoC) electrochemists have built sensors based upon CytoC immobilized onto metal electrodes. Previous studies have shown that the electron transfer rate through the protein is a function of the position of this heme group with respect to the electrode surface. In this study a detailed examination of CytoC orientation when electrostatically immobilized onto both amine (NH3+) and carboxyl (COO-) functionalized gold is presented. Protein coverage, on both surfaces, was monitored by the change in the atomic % N, as determined by x-ray photoelectron spectroscopy. Spectral features within the in situ sum frequency generation vibrational spectra, acquired for the protein interacting with positively and negatively charged surfaces, indicates that these electrostatic interactions do induce the protein into a well ordered film. Time of flight secondary ion mass spectrometry data demonstrated a clear separation between the two samples based on the intensity differences of secondary ions stemming from amino acids located asymmetrically within CytoC (cysteine: C2H6NS+; glutamic acid: C4H6NO+ and C4H8NO2+; leucine: C5H12N+). For a more quantitative examination of orientation, we developed a ratio comparing the sum of the intensities of secondary-ions stemming from the amino acid residues at either end of the protein. The 50 % increase in this ratio, observed between the protein covered NH3+ and COO- substrates, indicates opposite orientations of the CytoC on the two different surfaces.

Sub-nanosecond nuclear half-life and time-of-flight measurements with CeBr3

Abstract: CeBr3 is a new fast scintillator with timing and energy resolution similar to LaBr3:Ce. The excellent timing resolution, measured here to be 93 ps at 511 keV for 1 cm3 crystals, naturally lends itself to direct electronic measurements of excited nuclear state lifetimes in the nanosecond and sub-nanosecond range. To demonstrate this, half-lives of a 1.40 ns isomer in 152Sm and 537 ps isomer in 177Hf were directly measured using the delayed coincidence technique. With its fast timing, high light output and high efficiency, the possibility of CeBr3 as a time-of-flight PET detector was also explored through γ - ray time-of-flight measurements.

Accurate estimation of airborne ultrasonic time-of-flight for overlapping echoes

Abstract: In this work, an analysis of the transmission of ultrasonic signals generated by piezoelectric sensors for air applications is presented. Based on this analysis, an ultrasonic response model is obtained for its application to the recognition of objects and structured environments for navigation by autonomous mobile robots. This model enables the analysis of the ultrasonic response that is generated using a pair of sensors in transmitter-receiver configuration using the pulse-echo technique. This is very interesting for recognizing surfaces that simultaneously generate a multiple echo response. This model takes into account the effect of the radiation pattern, the resonant frequency of the sensor, the number of cycles of the excitation pulse, the dynamics of the sensor and the attenuation with distance in the medium. This model has been developed, programmed and verified through a battery of experimental tests. Using this model a new procedure for obtaining accurate time of flight is proposed. This new method is compared with traditional ones, such as threshold or correlation, to highlight its advantages and drawbacks. Finally the advantages of this method are demonstrated for calculating multiple times of flight when the echo is formed by several overlapping echoes.

A novel ion cooling trap for multi-reflection time-of-flight mass spectrograph

Abstract: A radiofrequency quadrupole ion trap system for use with a multi-reflection time-of-flight mass spectrograph (MRTOF) for short-lived nuclei has been developed. The trap system consists of two different parts, an asymmetric taper trap and a flat trap. The ions are cooled to a sufficient small bunch for precise mass measurement with MRTOF in only 2 ms cooling time in the flat trap, then orthogonally ejected to the MRTOF for mass analysis. A trapping efficiency of ≈ 27 % for 23Na+ and ≈ 5.1 % for 7Li+ has been achieved.

CO2 laser ionization of acoustically levitated droplets

Abstract: For many analytical purposes, direct laser ionization of liquids is desirable. Several studies on supported droplets, free liquid jets, and ballistically dispensed microdroplets have been conducted, yet detailed knowledge of the underlying mechanistics in ion formation is still missing. This contribution introduces a simple combination of IR-MALDI mass spectrometry and an acoustical levitation device for contactless confinement of the liquid sample. The homebuilt ultrasonic levitator supports droplets of several millimeters in diameter. These droplets are vaporized by a carbon dioxide laser in the vicinity of the atmospheric pressure interface of a time of flight mass spectrometer. The evaporation process is studied by high repetition rate shadowgraphy experiments elucidating the ballistic evaporation of the sample and revealing strong confinement of the vapor by the ultrasonic field of the trap. Finally, typical mass spectra for pure glycerol/water matrix and lysine as an analyte are presented with and without the addition of trifluoracetic acid, and the ionization mechanism is briefly discussed. The technique is a promising candidate for a reproducible mass spectrometric detection scheme for the field of microfluidics.

Time-of-flight neutron detection using PECVD grown boron carbide diode detector

Abstract: The development of novel neutron detectors requires an understanding of the entire neutron detection process, a process which depends strongly on material properties. Here we present accurate measurements of the neutron detection efficiency of an unenriched 640 nm thick boron carbide solid state neutron detector grown by plasma enhanced chemical vapor deposition as a function of the neutron wavelength at a time-of-flight facility. The data were compared to that obtained simultaneously by a calibrated nitrogen detector over the same wavelength range. The measured spectra of both detectors fit a Maxwell–Boltzmann wavelength distribution, thereby indicating that the boron carbide detector can be used as a reliable beam monitor. Measurements of the material properties (density, thickness and elemental composition) of the semiconducting boron carbide enable a precise calculation of the ideal expected neutron detection efficiency. The calculated neutron detection efficiency for the effective moderator temperature (obtained from a fit to the Maxwell–Boltzmann distribution) showed excellent agreement with the experimentally determined neutron detection efficiency of 1.25%. Higher efficiencies may be obtained either by increased film thickness and/or 100% 10B enrichment of the boron carbide source molecule.

Momentum imaging spectrometer for molecular fragmentation dynamics induced by pulsed electron beam

Abstract: A momentum imaging spectrometer has been built for studying the electron impact molecular fragmentation dynamics. The setup consists of a pulsed electron gun and a time of flight system as well as a two-dimensional time and position sensitive multi-hit detector. The charged fragments with kinetic energy up to 10 eV can be detected in 4π solid angles and their three-dimensional momentum vectors can be reconstructed. The apparatus is tested by electron impact ionization of Ar and dissociative ionization of CO2. By analyzing the ion-ion coincidence spectra, the complete and incomplete Coulomb fragmentation channels for CO2(2+) and CO2(3+) are identified. The kinetic energy release (KER) and angular correlation for the two-body breakup channel CO2(2+*) → O(+) + CO(+) are reported. The peak value of total KER is found to be 6.8 eV which is consistent with the previous photoion-photoion coincidence studies, and the correlation angle of O(+) and CO(+) is also explicitly determined to be 172.5°.

Ultrasonic measurement of micrometric wall-thickness loss due to corrosion inside pipes

Abstract: Pipelines are subject to wall-thickness loss due to corrosion along time. Ultrasonic pulse-echo techniques are widely used for thickness measurement achieving a high resolution. However, the precision of measurement is highly dependent on temperature and on the ultrasonic system. This work presents the temperature correction strategy of an ultrasonic measurement system to obtain one micron accuracy, in a pipeline corrosion long-lasting monitoring. The proposed technique is based on the fact that the coupling layer has a constant thickness during a long period of time (year) and can be used in the same way as a thermometer to compensate the changes in the ultrasonic velocity. The variation of time of flight in the coupling layer can relate to the variation of time of flight in the pipe wall to construct a correction polynomial. This function compensates the variation on propagation velocity and thermal expansion. The results are experimentally evaluated using an array of eight ultrasonic transducers (5 MHz, 10-mm diameter) operating in pulse-echo mode with a water coupling layer. Long term corrosion tests were conducted using an electrolytic bath along ten months. Good agreement was found between the theoretical corrosion rate and the results of the ultrasonic measuring system.

Low Energy Ion Scattering and Recoiling Spectroscopy in Surface Science

Abstract: This chapter presents an overview of low energy ion scattering spectroscopy and time of flight scattering and recoiling spectroscopy for the study of the structure and composition of surfaces as well as of fundamental ion surface interaction processes. The emphasis is on basic concepts regarding scattering, energy losses and charge transfer phenomena and experimental aspects involved in measurements of ion energies and time of flight measurements of scattered atoms. Some examples are provided to illustrate the type of information that can be obtained.

Analysis of time-of-flight distributions under pulsed laser ablation in vacuum based on the DSMC calculations

Abstract: A theoretical study of the time-of-flight (TOF) distributions under pulsed laser ablation has been performed. 2D simulations of pulsed evaporation of atoms into vacuum on the base of the direct simulation Monte Carlo (DSMC) method have been carried out. It is found that for large evaporating spots (when the spot radius exceeds the initial plume length by a factor of five) the TOF distributions practically do not change with the spot radius variation. Moreover, it is shown that such distributions can be obtained from 1D calculations. Thus, in the frames of 1D approach, the TOF distribution is a function only of the number of the evaporated monolayers, but not of the spot radius. The shape of the TOF distribution is shown to strongly depend on the amount of the evaporated matter. Based on the calculated TOF distributions, dependence of the particle kinetic energy on the number of the evaporated monolayers has been obtained. To verify the theoretical results, experimental data on laser ablation of niobium and mercury have been used, which confirm the obtained dependences. The obtained results allow estimating the irradiated surface temperature from the TOF distributions for monatomic neutral gas.

FOCUS: DEVELOPMENT AND APPLICATION OF TOF AND TOF/TOF MS: RESEARCH ARTICLE How Constant Momentum Acceleration Decouples Energy and Space Focusing in Distance-of-Flight and Time-of-Flight Mass Spectrometries

Abstract: Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energy and space distributions within an instrument's acceleration region and by the length of the field-free flight zone. With gaseous ion sources, these distributions lead to systematic flight-time errors that cannot be simultaneously corrected with conventional static-field ion-focusing devices (i.e., an ion mirror). It is known that initial energy and space distributions produce non- linearly correlated errors in both ion velocity and exit time from the acceleration region. Here we reinvestigate an old acceleration technique, constant-momentum acceleration (CMA), to decouple the effects of initial energy and space distributions. In CMA, only initial ion energies (and not their positions) affect the velocity ions gain. Therefore, with CMA, the spatial distribution within the acceleration region can be manipulated without creating ion-velocity error. The velocity differences caused by a spread in initial ion energy can be corrected with an ion mirror. We discuss here the use of CMA and independent focusing of energy and space distributions for both distance-of-flight mass spectrometry (DOFMS) and TOFMS. Performance characteristics of our CMA-DOFMS and CMA-TOFMS instrument, fitted with a glow- discharge ionization source, are described. In CMA-DOFMS, resolving powers (FWHM) of greater than 1000 are achieved for atomic ions with a flight length of 285 mm. In CMA-TOFMS, only ions over a narrow range of m/z values can be energy-focused; however, the technique offers improved resolution for these focused ions, with resolving powers of greater than 2000 for a separation distance of 350 mm.

Pixel circuit with controlled capacitor discharge time of flight measurement

Abstract: A pixel circuit includes a single photon avalanche diode (SPAD) and a measurement circuit including a capacitance. The SPAD detects an incident photon and the measurement circuit discharges the capacitance at a known rate during a discharge time period. The length of the discharge time period is determined by the time of detection of the photon, such that the final amount of charge on the capacitance corresponds to the time of flight of the photon. The pixel circuit may be included in a time resolved imaging apparatus. A method of measuring the time of flight of a photon includes responding to an incident photon detection by discharging a capacitance at a known rate and correlating final capacitance charge to time of flight.

Characterization of CdMnTe radiation detectors using current and charge transients

Abstract: Charge transport characteristics of Cd0.95Mn0.05Te: In radiation detectors have been evaluated by combining time resolved current transient measurements with time of flight charge transient measurements. The shapes of the measured current pulses have been interpreted with respect to a concentration of net positive space-charge, which has resulted in an electric field gradient across the detector bulk. From the recorded current pulses the charge collection efficiency of the detector was found to approach 100%. From the evolution of the charge collection efficiency with applied bias, the electron mobility-lifetime product of μnτn = (8.5 ± 0.4) × 10−4 cm2/V has been estimated. The electron transit time was determined using both transient current technique and time of flight measurements in the bias range of 100–1900 V From the dependence of drift velocity on applied electric field the electron mobility was found to be μn = (718 ± 55) cm2/(V.s) at room temperature.

Thermal ionization time-of-flight mass spectrometer and thermal ionization time-of-fight mass spectrometric analysis method

Abstract: The invention provides a thermal ionization time-of-flight mass spectrometer and a thermal ionization time-of-fight mass spectrometric analysis method, and belongs to the technical field of mass spectrometric analysis The thermal ionization time-of-flight mass spectrometer is mainly composed of an ion source, an ion transmission system and a vertical reflection type time-of-flight mass analyzer The thermal ionization time-of-flight mass spectrometer is used, an analysis sample is arranged in the ion source and fixed on a filament band on a sample frame, currents of the filament band are increased to enable the sample to be ionized, ion beams are transmitted and modulated by an ion transmission lens assembly in the ion transmission system and reach the vertical reflection type time-of-flight mass analyzer, ions with different masses reach a detector after different flight time, and the qualitative and quantitive analysis or the isotope analysis of the sample is achieved According to the thermal ionization time-of-flight mass spectrometer and the thermal ionization time-of-fight mass spectrometric analysis method, isotope abundance can be quickly and accurately measured, impurity elements are monitored, and an innovative mass spectrometric analysis technology is achieved

Time-of-flight detector applied to mass measurements in Rare-RI Ring

Abstract: A large time-of-flight (TOF) detector has been developed for the Rare-RI Ring. This detector consists of a Multi Channel Plate (MCP) and a carbon foil. Secondary electrons from the carbon foil are transported to the MCP by crossed electric and magnetic fields. In order to cover the beam size of the ring, a large and thin carbon foil (100 mm × 50 mm2 and 60 μ g/cm2) is used as a sensitive material. The time resolution of σ ≈ 130 ps, the detection efficiency about 56% and a position dependence of the TOF about 1 ns are obtained. A calculated position dependence of TOF adopting experimental (inhomogeneous) electric field and a homogeneous magnetic field is in agreement with the experimental one. These results suggest that the homogeneity of electric field is important to improve the time resolution in the large size detector.