Showing papers on "Time of flight published in 1976"

Acoustic examination, material characterization and imaging of the internal structure of a body by measurement of the time-of-flight of acoustic energy therethrough

Abstract: Pulses of acoustic energy are transmitted from a plurality of different directions through a plane of interest, or a number of adjacent planes of interest, of a body to be examined. The body may be biological or non-biological. Time-of-flight of the pulses is measured for individual paths through the body, and from the data thus obtained the spatial distribution of the acoustic velocity through the plane or planes within the body is reconstructed using a mathematical reconstruction technique. The velocity values thus obtained, which are uniquely determinative of the acoustic index of refraction at each point, have diagnostic value, and they can further be displayed by means of a cathode ray tube or other imaging device to provide an image of the internal structure along each plane. The disclosed technique has the advantage of being highly independent of acoustic attenuation and reflections occurring along the paths.

Time-of-flight mass spectrometer

Abstract: The invention relates to a nonmagnetic time-of-flight mass spectrometer whose analyzer chamber accommodates a pulsed ion source, an ion detector and an ion reflecting system disposed on one and the same ion-optical axis. The ion detector and the ion reflecting system are disposed on opposite sides of the ion source. The ion source comprises a source wherein all electrodes are transparent to the ions studied.

Autoionization of N2 studied using an electron time-of-flight coincidence spectrometer

Abstract: Autoionizing states of N2 have been studied using a new electron-electron coincidence technique, by simultaneous measurement of their excitation energies and ejection energies in decay to states of N2+. This method gives a much clearer understanding of molecular autoionization than methods which measure either energy separately. Low energy electron impact is employed using hemispherical analysers to select the incident beam and to detect scattered electrons which have excited a selected autoionizing level. In coincidence with these scattered electrons, ejected electrons are analysed by measurement of their flight times along a field-free region. Transitions between the selected autoionizing level and levels of N2+ appear as peaks in the time spectra. The design, construction and operation of the spectrometer are discussed and factors limiting the time and energy resolutions are considered. Results are presented showing time spectra for electrons ejected from five autoionizing states of N2 and good agreement is observed between the predicted and measured resolutions of the spectrometer.

New laser-induced fluorescence method for molecular beam velocity analysis

Abstract: We have measured the velocity distribution of a Na2 supersonic beam by a time of flight method in which a chopped beam from an argon ion laser depopulates a single vibration–rotation level of the Na2 ground electronic state, and a continuous laser beam further downstream is used to detect the arrival of the tagged molecules by observation of changes in the laser‐induced fluorescence

Neutron-proton forward elastic scattering from 58 to 391 MeV

Abstract: Elastic neutron-proton differential cross sections have been measured between 58 and 391 MeV incident neutron energy at angles in the center-of-mass system from 11 degree to 54 degree . Neutrons were scattered from a liquid- H$sub 2$ target and detected in liquid scintillators. The incident energy of each detected neutron was determined from its time of flight. The data were normalized by placing the detector in the beam. The results are generally consistent with previous data and with the predictions of phase-shift analysis but are of improved accuracy. (AIP)

Time-of-Flight Scattering Spectroscopy

Abstract: Publisher Summary This chapter discusses the time-of-flight (TOF) scattering spectroscopy. TOF spectroscopy consists of many groups, each of which is only concerned with one type of particle and a limited energy range. Measurement of the flight time t of a single particle traversing a well-defined flight path of length L yields the particle velocity υ = L / t . The compilation of flight-time values measured for a great number of beam particles gives a flight-time distribution from which the velocity or the energy distribution can be calculated. The time at which the particle enters the flight path is defined by the action of a beam gate and marked by an electronic gate signal; the second time-mark is given by the electronic signal from a fast-response particle detector at the end of the flight path. In a special form of singleshot operation, TOF measurements are performed on continuous particle beams without the use of a beam gate; the particle to be timed provides a signal when it enters the flight path, for example, by penetrating a transmission detector. This is called single-particle zero-time pick off. TOF scattering spectroscopy is applied in many different fields. For spectroscopy with high energy neutrons, it is the only high-resolution method available. The two greatest advantages of TOF spectroscopy are its conceptual simplicity and its excellent compatibility with computerization.

Separation of isotopes by time of flight

Abstract: One of the isotopes of an element having several isotopes can be separated from the others in a dense, neutral plasma. Thus initially a neutral plasma is prepared including the element in question. This may consist of positive ions and negative electrons or alternatively of positive and negative ions, or else of a mixture of positive ions, negative ions and electrons. The plasma may then be injected into a magnetic field or may be generated in the field where more energy is imparted to a selected isotope than to the others. Finally, the isotopes are separated from each other on the basis of their differential energies. For example, the selected isotope may be given more energy than the others by stimulating it within the plasma at its resonant frequency which may be close to the cyclotron frequency, either by an electric field or by a magnetic field. In order to excite the other isotope, a different resonant frequency is required which depends on the plasma density, the relative concentration of electrons if the plasma contains electrons, the strength of the magnetic field, the ratio of charge to mass of the isotope, and possibly on the physical parameters of the plasma apparatus itself, such as the ratio of the length of the plasma column to its radius. The more energetic isotope may be separated by energy dependent chemical reactions, it may be collected by a positively biased probe or else the isotopes may be separated from each other by magnetic fields or in various other ways.

Time‐of‐flight energy spectrometer for positive ions

Abstract: A technique is described for the simultaneous measurement of the time‐of‐flight and energy of positive ions produced in the decay of excited molecules. The technique permits the separation and determination of the energy spectra of ion species with different mass to charge ratios. Data from the bombardment of CO by 1‐MeV He+ are presented.

The Frankfurt EBIS with Time-of-Flight Operation

Abstract: An EBIS with dc output has been built running in a time-of-flight mode of operation, e.g., the ions become highly charged during the time of flight in the electron beam from one end of the source to the other. Design principles to produce current densities above 103 A/cm2 have been applied in constructing the source, including a high power electron gun and magnetic compression of the accelerated beam. First tests on the ionization of Argon show that desorption requires attention at the electron collector. Cathode extraction of ions has proved to be quite satisfactory, promising great flexibility in producing ions from any element, gaseous or solid.

Metastable hydrogen atom detector suitable for time‐of‐flight studies

Abstract: A selective detection scheme for atoms in the metastable 2s state of hydrogen that provides the high spatial resolution (0.1 cm) necessary for time‐of‐flight atomic‐beam studies is described. The scheme utilizes the Lyman α photon emitted when the metastable is de‐excited in an electric field via the Stark effect. Details of construction and operation are discussed.

Atomic Mass Measurements Using Time-of-Flight Mass Spectroscopy

Abstract: We describe herein a new approach to precise mass measurements using time-of-flight mass spectroscopy. The spectrometer has been designed to operate in the “on-line” mode coupled with the He-jet system,1 or to be used off-line with stable species.2 Although time-offlight mass spectroscopy is not normally associated with precision work, accurate mass measurements can in principle be accomplished by the use of long flight paths and modern timing instrumentation. It is the long-range goal of this work to directly measure the masses of nuclei far from stability.

Low energy time-of-flight spectra from spheres pulsed by 14-MeV neutrons

Abstract: 1 ^ Introduction 1 txperimental MutKod -. 1 " Experimental Results 2 i Compar ison w i t h C a l c u l a t i o n s 3 lU'knowledgmeni s , 5 R e f e r e n c e s , , . 6

Precision Measurement of Q-Values by Means of the Munich Time-of-Flight System and the Q3D-Spectrograph

Abstract: The measurement of Q-values of nuclear reactions is one of the most important methods for determining the masses of unstable nuclei which has contributed much to the present knowledge of nuclear masses. In most cases reactions with charged particles in the entrance and exit channel were used and the Q-value was determined by measurement of the magnetic rigidity of both the bombarding particles and the reaction products in homogeneous field iron magnets. Although the magnetic induction B itself can be measured to about 10−6 by means of nuclear magnetic resonance the magnetic rigidities Bδ and thus the particle energies could be obtained only with accuracies of some parts in 104 /1/. This is mainly caused by two effects: 1) Even in high quality iron magnets the average field may deviate from the field of the location of the NMR probe by some parts in loo. Furthermore this difference may change by about 10−4 due to differen­tial hysteresis. 2) In the determination of the magnetic rigidity of the bombarding particles in the analyzing magnets a further uncertainty arises from the finite object and image slit width. Therefore the radius of the trajectories of the particles is usually not defined better than to about 5•10−4. Thus the actual radius of curvature may deviate from the nominal radius defined by the centres of the slits by a few parts in 104 because of asymmetries in the beam profiles at the slit positions.

Computer-controlled time-of-flight atom-probe field-ion microscope for the study of defects in metals

Abstract: A time-of-flight (TOF) atom-probe field-ion microscope (FIM) specifically designed for the study of defects in metals is described. This atom probe features (i) a variable-magnification internal image-intensification system based on a channel electron multiplier array for viewing the FIM image; (ii) a liquid-helium-cooled goniometer stage which allows the specimen to be maintained at a temperature anywhere in the range 13-450K; (iii) a low-energy (

a Study of the Analogy Between Ion and Light Spectrometry Leading to the Development of a New Dynamic Mass Spectrograph.

Abstract: The main result of this thesis work is the design, construction and utilization of a new, dynamic, time of flight charged particle spectrograph. During the development of this concept an attempt has been made to put this spectrograph in its logical place among other ion analyzing instruments and their optical analogues. In presenting this work we have attempted to summarize some of the more important phenomena which have their analogues in ion and light optics, in particular those relating to dispersing elements. The text summarizes the general analogy between the two fields, beginning with basic principles, deriving some of the anologous parameters and pointing out the limitations to these analogies. The initial motivation for this work was the need for a technique to measure simultaneously the yield, charge, mass, and energy carried away by ions that are blown off laser produced plasma experiments. Since these experimental laser shots differ from each other in power, focusing and target geometry it is essential to take the distributions of the above mentioned parameters during a single experiment. The only technique available by the time that this work was started was to use the well-known Kaufmann-Thompson parabola spedtrograph. This technique had the disadvantage of.collecting the ions on a photographic film and troublesome calibration due to the fact that exposure is not only yield dependent but also energy dependent. The effort of this research was therefore directed toward finding a new charge to mass (q/m) path stability field (analogous to wave length stability path in optical spectrometry), or combination of fields, where (q/m) will be determined by path stability and the velocity by time of flight methods. Here we take advantage of the fact that all the ions are created during a short time interval compared to their time of flight. This is a situation typical for many kinds of short duration events, e.g., sparks, surface composition determination using lasers, and laser induced plasmas. The resulting spectrometer was an electro-dynamic spectrograph having a (q/m) path stability over the whole range of ions analyzed. This spectrograph and some of the experimental results are described in the text. An optical spectrograph, analogous to ion optical spectrographs, having a space varying index of refraction, is proposed. There we try to adopt solutions already known from ion optics and show their spectral dispersion.as well as focusing properties. It is clearly seen here that the analogy serves as a vehicle for transferring solutions from one field to another. A variety of other applications, stimulated by looking at both the ion and light optics, are discussed in the text and appendices.

Measurement of the velocity of a rarefied gas flow using an ionic tag

Abstract: The article expounds a method for measuring the velocity in a flow close to free-molecular from the motion of an ion tag, formed using an electron beam. It examines the effect of the field of the beam and of the inherent volumetric charge of the tag on the results of the measurements; the conditions under which this effect can be neglected are calculated. The velocity In highly rarefied jets of nitrogen and argon was measured. The method of an ion tag, for example [1, 2], consists in the fact that the gas is ionized (tagged) using a narrow pulsed beam of electrons, and the velocity of the gas is determined from the time of flight of the tag from a known base. The tag consists in an ion cloud, since the electrons forming with ionization of the gas have an energy of several electron volts and leave the flow after a time te which is small in comparison with the time of the motion of the ions ti (te<10−2ti). The presence of the inherent volumetric charge of the ion cloud leads to washing-out of the ion tag and to its additional acceleration. With an increase in the degree of rarefaction, particularly in a free-molecular flow, where the ions move without collisions with the molecules of the flow, the effect of the inherent fields increases, and the velocity of the tag may differ considerably from the velocity of the neutral gas. Insufficient attention has been paid to this question in the literature.

A molecular beam time-of-flight method for the observation of the velocity dependence of total collision cross sections

Abstract: An application of the molecular beam time-of-flight technique is presented providing a physically simpler method of overcoming the principal uncertainties encountered in measurement of the velocity dependence of total collision cross sections. Explicit expressions are given for the velocity resolution and transmission of the time-of-flight (TOF) system. The considerations and procedure for design of a molecular beam TOF apparatus are detailed. This method gives greater velocity range and freedom of control of velocity resolution and transmission than traditional methods. The apparatus is described with emphasis on the considerations for optimizing the signal to noise ratio. An example of the method of extraction of the total cross section from the data is given, together with the observed velocity dependence and resulting intermolecular potential information.

Measurement of space potential by the time of flight of heavy ions

Abstract: The authors have developed a technique to measure potential variations produced by space charge. The method consists in directing a beam of fast heavy ions through the region of interest and measuring the time of flight. The flight time is measured by intensity-modulating the beam and detecting the resulting phase shift between the collector and the ion source. Results of experiments performed using a simulator show that a direct reading can be obtained of potential changes of a few volts with a temporal resolution of about 10 mu s.

A Rotating Crystal Time of Flight Spectrometer Using a Pulsed Neutron Source(Physics)

Abstract: The design and construction of a rotating crystal spectrometer for use with a pulsed neutron source is described. The source is the tungsten target of a 33 MeV electron linear accelerator, and at 5 kV mean power the spectrometer performance is equivalent to that of a similar instrument mounted on a nuclear reactor of 4 × 1012 n/cm2 s flux. Future developments will give an order of magnitude overall improvement. This spectrometer has been shown to be useful for studies of dense gases and liquids using an incident neutron wavelength of 2.4 A, and its performance at wavelengths between 0.5 and 6.2 A has been assessed.