A time-of-flight detector of low-energy ions for an accelerating mass-spectrometer

The results of experiments with a time-of-flight detector for detecting rare ions at the output of the accelerating mass spectrometer of the Institute of Nuclear Physics (Siberian Branch, Russian Academy of Sciences) are described. The operation of this detector is based on detection of electron emission from thin films by means of microchannel plates. Owing to the small thickness of films, ions can sequentially pass through several films—this is the basis of the time-of-flight system for identifying isotopes. The high time resolution of detectors allows a significant decrease in the external-radiation background compared to one semiconductor complete-absorption detector that measures the ion energy.     

Status and possibilities of the time-of-flight measurement technique using long scintillation counters with a small cross section (Review)

Results of the analysis of the state-of-the-art time-of-flight measurement technique with the use of long scintillation counters with a small cross section (the length of the counter far exceeds its width in the plane of the hodoscope and thickness along the beam direction), which are used as basic elements of time-of-flight detectors for large physical installations and intended for identifying secondary particles generated during collisions of high-energy particles. The following issues are considered in this review. Various methods for identifying particles are compared, and it is pointed out that the time-of-flight method has certain advantages for secondary particles with momenta higher than ～3–5 GeV/c. Some elements incorporated in scintillation counters and affecting its time resolution are considered: optical fibers, optical contacts in the scintillator-fiber-photodetector system, and high-frequency cables. Their characteristics are presented. The characteristics of all elements of a counter (scintillator, photodetector (PD), and electronics) and the processes occurring in them are discussed. The presented experimental data show that, under the conditions of high counting rates and strong magnetic fields, the working capacity of counters holds at a time resolution of ～100–200 ps. The results of measuring the operating characteristics of counters are analyzed. The dependences of the time resolution on such variables as the coordinate of the particle transit through a counter along its length, the counter length, the light-absorption length in the scintillator, the quality of treatment of the scintillator’s surface, and the energy deposited by a particle in the scintillator substance are considered. The main characteristics of individual time counters and average parameters of time-of-flight detectors in certain physical facilities are presented. Possible ways to improve the time resolution and reduce it to ～50–100 ps are considered.     

MIR-TOF-MS在多肽分析中的应用

应用实验室研制成功的高分辨飞行时间质谱仪的分子离子反应器 ( Molecular ion reactor,MIR)接口来分析多肽结构和获得相关信息。实验结果表明 :MIR能够有效地破碎多肽 ,得到准确的碎片信息 ,是一种理想的多肽结构分析技术。     

Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules

This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5-3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer.     

Secondary Ion Time-Of-Flight Mass Spectrometers and Data Systems

ABSTRACT

Some recent improvements to the Manitoba linear time-of-flight mass spectrometer are reviewed. A new data system gives greatly improved performance. A detector assembly with a small 45° ion mirror and separate detectors for neutral and charged particles has been added. In conjunction with the new data system, it enables measurement of correlations between neutral and charged fragments resulting from unimolecular decay in the flight tube.

A new time-of-flight spectrometer has been constructed. It is a reflecting instrument with a relatively long ion mirror. Resolution and signal/background ratio are much better than in the linear instrument, and correlation measurements can be made with considerably higher accuracy in mass determination than with the small mirror.     

Time-of-flight photoelectron spectroscopy of gases using synchrotron radiation

A gas-phase time-of-flight (TOF) photoelectron spectrometer has been developed for use with synchrotron radiation. The excellent time structure of the synchrotron radiation at the Stanford Positron Electron Accelerator Ring (SPEAR) has been used as the time base for the TOF measurements. The TOF analyzer employs two multichannel plates (MCPs) in tandem as a fast electron multiplier with a matched 50-Omega anode to form an electron detector with a timing resolution of 相似文献   

Energy-sensitive cryogenic detectors for high-mass biomolecule mass spectrometry

Energy-sensitive calorimetric detectors that operate at low temperatures ("cryogenic detectors") have recently been applied for the first time as ion detectors in time-of-flight mass spectrometry. Compared to conventional, ionization-based detectors, which rely on secondary electron formation or the charge created in a semiconductor, cryogenic detectors measure low-energy solid state excitations created by a particle impact. This energy sensitivity of cryogenic detectors results in several potential advantages for TOF-MS. Cryogenic detectors are expected to have near 100% efficiency even for very large, slow-moving molecules, in contrast to microchannel plates whose efficiency drops considerably at large mass. Thus, cryogenic detectors could contribute to extending the mass range accessible by TOF-MS and help improving detection limits. In addition, the energy resolution provided by cryogenic detectors can be used for charge discrimination and studies of ion fragmentation, ion-detector interaction, and internal energies of large molecular ions. Cryogenic detectors could therefore prove to be a valuable diagnostic tool in TOF-MS. Here, we give a general introduction to the cryogenic detector types most applicable to TOF-MS including those types already used in several TOF-MS experiments. We review and compare the results of these experiments, discuss practical aspects of operating cryogenic detectors in TOF-MS systems, and describe potential near future improvements of cryogenic detectors for applications in mass spectrometry.     

Picosecond Fluorescence Spectroscopy By Time-Correlated Single-Photon Counting

Abstract:

We describe the recent progress made in our laboratory on the time-resolved fluorescence spectroscopy by the combination of stable short-duration pulses from a CW mode-locked laser and a time-correlated single-photon counting method. Particular emphasis is placed on the achievement of high time resolution with side-on and microchannel-plate photomultipliers. We also discuss the limitation of using this method in the picosecond time range. Several applications of this spectroscopy such as the measurements of fluorescence decay characteristics and time behavior of fluorescence depolarization are reported. It is also shown that the high sensitivity of this method with pico-second time resolution is very suitable for the temporal rejection of cumbersome background-fluorescence in Raman spectroscopy. Finally, we present a novel method of photon time-of-flight fluorescence spectroscopy, in which an optical fiber is employed as a dispersive element.     

Combining high mass resolution and velocity imaging in a time-of-flight ion spectrometer using pulsed fields and an electrostatic lens

We describe a momentum resolving time-of-flight ion mass spectrometer that combines a high mass resolution, a velocity focusing condition for improved momentum resolution, and field-free conditions in the source region for high resolution electron detection. It is used in electron-ion coincidence experiments to record multiple ionic fragments produced in breakup reactions of small to medium sized molecules, such as F(3)SiCH(2)CH(2)Si(CH(3))(3). These breakup reactions are caused by soft x rays or intense laser fields. The ion spectrometer uses pulsed extraction fields, an electrostatic lens, and a delay line detector to resolve the position. Additionally, we describe a simple analytical method for calculating the momentum from the measured hit position and the time of flight of the ions.     

Improvement of the intrinsic time resolving power of the Cologne iron-free orange type electron spectrometers

Conversion electron spectroscopy represents an important tool for nuclear structure analysis of medium and heavy nuclei. Two iron-free magnetic electron spectrometers of the orange type have been installed at the Institute for Nuclear Physics of the University of Cologne. The very large transmission of 15% and the very good energy resolution of 1% makes the iron-free orange spectrometer a powerful instrument. By means of fast timing techniques, lifetimes of nuclear excited states can be measured with an accuracy better than 20 ps. For the first time, the energy dependent centroid position of prompt events yielding the time-walk characteristics (the prompt curve) of the orange spectrometer fast timing setup has been measured using prompt secondary δ-electrons generated in a pulsed beam experiment. The prompt curve calibrated as a function of energy allows precise lifetime determination down to a few tens of picoseconds by the use of the centroid shift method.     

An imaging proton spectrometer for short-pulse laser plasma experiments

The ultraintense short pulse laser pulses incident on solid targets can generate energetic protons. In addition to their potentially important applications such as in cancer treatments and proton fast ignition, these protons are essential to understand the complex physics of intense laser plasma interaction. To better characterize these laser-produced protons, we designed and constructed a novel spectrometer that will not only measure proton energy distribution with high resolution but also provide its angular characteristics. The information obtained from this spectrometer compliments those from commonly used diagnostics including radiochromic film packs, CR39 nuclear track detectors, and nonimaging magnetic spectrometers. The basic characterizations and sample data from this instrument are presented.     

A setup for studying rare decays of heavy and superheavy elements

A new setup composed of 32 pairs of semiconductor detectors, systems of data acquisition, storage, and processing, and a vacuum system has been developed at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. The setup can be used for low-background measurements and is intended to study radioactive decays of relatively long-lived isotopes of heavy and superheavy elements in a geometry close to 4π.     

A photoelectron velocity map imaging spectrometer for experiments combining synchrotron and laser radiations

A velocity map imaging/ion time-of-flight spectrometer designed specifically for pump-probe experiments combining synchrotron and laser radiations is described. The in-house built delay line detector can be used in two modes: the high spatial resolution mode and the coincidence mode. In the high spatial resolution mode a kinetic energy resolution of 6% has been achieved. The coincidence mode can be used to improve signal-to-noise ratio for the pump-probe experiments either by using a gate to count electrons only when the laser is present or by recording coincidences with the ion formed in the ionization process.     

Detecting system of the setup for studying chemical properties of superheavy elements using the gas chemistry techniques

A setup for studying the physicochemical properties of superheavy elements in experiments involving gas transport systems is described. The setup is composed of four detecting modules with semiconductor detectors; systems of data acquisition, storage, and processing; a cooling system for semiconductor detectors; and a vacuum system. In each detecting module, there are two oppositely located four-strip semiconductor detectors. The detecting system is capable of detecting with a high efficiency α particles and spontaneous fission fragments produced in decays of superheavy elements.     

Scanning electron microscope design for quantitative multicontrast

Conceptual designs of scanning electron microscopes (SEMs) using a time-of-flight electron spectrometer are presented. The procedure for making quantitative measurements with such SEMs is shown to be much simpler and versatile than using conventional SEMs. SEMs which use an electron time-of-flight spectrometer are able to operate as multicontrast analytical probes, capable of simultaneously quantifying surface topography, voltage, and material type. In addition, it is demonstrated that these SEMs can be designed to have high spatial resolution, good signal-to-noise characteristics, and to be of compact table-top size.     

The MPD test beam setup for testing detectors with the Nuclotron beams

A new specialized MPD Test Beam setup was mounted at the extracted beam of the Nuclotron at the Joint Institute for Nuclear Research to carry out methodical research and test detectors produced for the MPD experiment at the NICA accelerating facility. The setup is described in detail. The results of the testing of fast detectors for the MPD time-of-flight system are presented as an example of the operation of the setup.     

A spectrometer for seeking exotic states of pionic atoms of xenon

The parameters of a spectrometer for searching for deeply bound pionic states of xenon are presented. The main component of the spectrometer is a multilayer semiconductor telescope based on high-purity germanium detectors. A technique for calibrating the spectrometer and measuring its energy resolution using reactions p(d, ³He)π⁰ and ¹⁴N(d, ³He)¹³C is described. The energy resolution of the setup is shown to be 0.85 MeV for ³He ions with an energy of ～360 MeV.     

Proton emission from thin hydrogenated targets irradiated by laser pulses at 10(16) W∕cm2

The iodine laser at PALS Laboratory in Prague, operating at 1315 nm fundamental harmonics and at 300 ps FWHM pulse length, is employed to irradiate thin hydrogenated targets placed in vacuum at intensities on the order of 10(16) W∕cm(2). The laser-generated plasma is investigated in terms of proton and ion emission in the forward and backward directions. The time-of-flight technique, using ion collectors and semiconductor detectors, is used to measure the ion currents and the corresponding velocities and energies. Thomson parabola spectrometer is employed to separate the contribution of the ion emission from single laser shots. A particular attention is given to the proton production in terms of the maximum energy, emission yield, and angular distribution as a function of the laser energy, focal position, target thickness, and composition. Metallic and polymeric targets allow to generate protons with large energy range and different yield, depending on the laser, target composition, and target geometry properties.     

Measuring the nuclear charge of fission fragments using a large ionization chamber—part of the double-arm time-of-flight spectrometer

Identification of decay products is a relevant task in studying rare collinear decays of low excited heavy nuclei. A technique for measuring the nuclear charge of decay products detected by a wide-aperture ionization chamber—a part of the double-arm time-of-flight spectrometer—is described. Two versions of nuclear charge calibration using data of the reaction ²³⁵U(n _th, f) have been developed to determine the charge of the decay products. Testing with simulation data shows that the use of charge parameterization based on the Bohr-Willer empirical equation in the calibration procedure makes it possible to determine the nuclear charge of the fission fragments over a wide energy range. The charges of light ions from He to C, predicted on the basis of this approach, appear to be overestimated by two charge units.     

Laboratory nuclear-physics methods for determining the characteristics of charged particle silicon detectors

A review is presented of “nontraditional” laboratory nuclear-physical methods for determining key parameters of charged-particle semiconductor detectors, such as the sensitive depth and the energy resolution. The methods for measuring the sensitive depth are based on the peculiarities in interactions of radiation from standard α,β, and γ sources and monochromatic neutrons with the detector materials and require that several “reference” detectors with known characteristics be available. Using the proposed methods, it is possible to preliminarily estimate the serviceability of detectors before employing them in expensive experiments, e.g., on accelerator beams.