Source Of Low-energy Electrons Research Articles

Formation of water and ammonia cluster anions by electron transfer from laser excited Rydberg atoms

Using a laser excited Rydberg atomic beam as a very low energy (10-270 meV) electron source, we have investigated the experimental conditions for observation of water (from dimer to 40-mer) and ammonia cluster anions. From simple model calculations, estimates of the small water cluster adiabatic electron affinities have been determined as well as the orders of magnitude of autodetachment lifetimes and attached electron critical energies.

Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms

Electron attachment to SO2 clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbersn, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations.

Holography with low-energy electrons.

We have employed an ultrasharp tip, prepared by field-ion techniques, as a coherent point source of low-energy electrons. The source, which constitutes the origin of a spherical electron wave, is positioned close to small carbon fibers, at which some of the electrons are elastically scattered. At macroscopic distances a hologram is observed, which arises from the interference of the scattered electrons with the reference wave. The high magnification of the interference pattern is brought about purely by geometric projection. No electron lenses are emloyed and, thus, the high-resolution microscopic information gained by this novel technique is not affected by aberrations.

Time-of-flight secondary ion mass spectrometry of insulators with pulsed charge compensation by low-energy electrons

A new charge compensation system for time-of-flight (TOF) secondary ion mass spectrometry is described. A pulsed low-energy electron source (10 eV) in combination with a pulsed extraction voltage of the TOF analyzer allows low-energy electrons to reach the target in the relatively long period of time between two excitation pulses. Low-energy electrons allow self-adjusting of the surface potential. Sample damages by these electrons are not detectable. Effects due to electron stimulated desorption are suppressed by pulsing the anode of the electron source. Compensation is possible for the accumulation of positive as well as negative spectra. With this experimental arrangement we investigated a variety of insulating materials (e.g., thick polymer films, glasses, ceramics). In all cases we found stable and reproducible spectra, even of insulators with extremely low conductivity.

Preparation of Low-Energy Reference Electron Source with 169Yb

Large sized and uniformly deposited 169Yb sources were prepared with the following properties: the intensity variation and the deposited thickness were <±8% and ∼0.4 µg/cm2, respectively, for the source sizes of 35×45 mm2 and 20×100 mm2 with the deposited activity of 20-50 µCi, as an energy reference source for the neutrino mass measurement at INS. The technical details of the preparation: the processes of chemical separation and purification, and vacuum-deposition, are here reported.

TOF‐SIMS analysis of the surface of insulators. Examples of chemically modified polymers and glass

AbstractA metod to compensate for surface charging of insulator surfaces during TOF‐SIMS experiments is described. For this purpose a pulsed low energy electron source is used, immediately after the ion extraction period. The surface potential is self adjusting, resulting in a stable spectrum. Besides, ESD effects are strongly suppressed. Positive and negative ion spectra of thick PMMA and PC substrates, containing surface active additives and of UV‐ozone cleaned glass substrates before and after trimethylsilylation are presented. From the glass samples the positive ESD spectra were also recorded by using a continuous electron beam. Comparison between the SSIMS and ESD results indicates that ESD is more surface sensitive and sufferes less from ion fragmentation than SSIMS.

Energy Response of Hot-Pressed Thin Layer Detectors to Photon and Electron Irradiations

Abstract Hot-pressed thin layer detectors for integrating solid state dosemeters (C/B/Al2O3/LiF:Mg,Ti and Al/Al2O3/LiF:Na,Mg,Ti structures) were investigated with respect to sensitivity for X and ? irradiations with different energies (6 keV - 1 MeV) and variable radiation incidence (±60o isotropy) with and without the presence of phantoms. TL and TSEE readouts showed characteristic over- and under-estimations of the applied doses. The TL response of the new detectors to ß irradiations (90Sr-90Y, 204Tl, 147Pm) meets the requirements of practice by decreasing only for the low energy electron source.

A low-energy electron source for negative ionization experiments

A negative ionization source for a quadrupole mass analyzer is described. The ionization region can be exposed to laser light for the purpose of determining the effect of molecular excitation on electron capture cross-section. The low-energy electron source possesses an ionization region of approximately cylindrical geometry, the key element of which is an open helical grid. A flat-plate energy analyzer permits location of the electron gun at a position remote from the ionization region. The sensitivity of the system, ionization source plus quadrupole mass analyzer, for production of anions of sulfur hexafluoride has been found to be (0.013 ± 0.001) torr −1. A discussion of the qualitative aspects of source operation is also given.

Cryogenic photoemissive electron source

A compact, low-energy electron source for use at cryogenic temperatures is described. The device uses quartz optical fibers and a discharge lamp to excite photoelectrons from a cold zinc emitter. Picoampere currents are obtained with low heating. The source has been used in studies of surface-state electrons on liquid helium.

Ionizing Radiation Effects in Inversion Layer Silicon Solar Cells

Ionizing irradiation experiments on a new inversion layer solar cell have been carried out to determine its potential for space applications. A scanning electron microscope was used as a source of low energy (2-12 keV) electrons in doses up to 1014 e/cm2. Phototopographic scanning and C-V analysis were used to determine the effects of the radiation on the Si02-Si system. The electron irradiation results are validated by comparison with those of a conventional X-ray experiment. The operation, fabrication and electrical characteristics of the cell are also discussed. Large increases in both the oxide charge and surface state density were observed, but little change occurred in the cells' output characteristics below 105 rads (Si). A drop-off in power at higher doses is explained in terms of surface recombination and series resistance increases. The results of isochronal and UV annealing experiments on these effects are also presented. The cells are concluded to have potential for use in space.

A Thermionic Point Source of Low Energy Electrons

A novel type of electron gun is described in which a spherically symmetric field is simulated. The structure is hemispherical: The inner hemisphere is a space-charge-limited emitter, and the outer concentric hemisphere is the anode. The hemispheres are terminated by a plane electrode with a radial potential variation designed to match the field between concentric spheres. This field is known from a new numerical solution to Poisson's equation. The energy distribution produced by the gun is measured and compared with the calculated distribution.

A Low Energy Electron Source for Mobility Experiments

Thin film Al–Al2 O3–Au diodes were used as sources of low energy electrons (∼1 eV) in a drift velocity spectrometer. These diodes were found to offer several advantages over other sources used for electron mobility studies in dense gases and liquids.

Electron and Proton Fluxes in the Trapped Radiation Belts Originating from an Orbiting Nuclear Reactor

Abstract : A simple calculation is done to determine the effects of an orbiting nuclear reactor on the trapped radiation belts. A SNAP-50 reactor, in an equatorial orbit at 1000 km and operating at 8 megw/thrm for a period of one year, is considered as a source of low energy electrons and protons. Neutrons escaping from the reactor decay into electrons and protons and these can become trapped in the earth's magnetic field. Hence, they contribute to the natural fluxes in the radiation belts. Three different source problems are considered: 1.) those neutrons which decay within one kilometer of the reactor; 2.) those neutrons which decay within the entire inner radiation belt; 3.) those neutrons which decay within the entire outer radiation belt. In each region the average equilibrium of reactor-produced electron and proton fluxes at the equator are calculated after reactor operation for one year. These fluxes are compared to the average natural electron and proton fluxes in the regions, and the reactor- produced fluxes are found to be less than 0.1 percent of the natural fluxes in all three cases. All assumptions and calculations are presented in sufficient detail to allow updating with more recent or more exact information.

A simple electron gun for use in electron scattering studies

The design, construction and performance of a simple electron gun is described, the principle advantage of which is the employment of a filament derived from an ordinary pocket torch lamp bulb. The described electron gun, used in electron scattering studies, has proved itself very suitable as a source of low energy electrons and requires a minimum of service. In conclusion the angular distribution of the electron beam intensity, is presented.

The Stanford medical linear accelerator. II. Installation and physical measurements.

The electron linear accelerator is an instrument for the acceleration of electrons to high energies by means of guided electromagnetic waves. It may serve as a source of both energetic electrons and x-rays, the latter being obtained by bremsstrahlung conversion in materials of high atomic number. Both types of radiation are of interest in the field of cancer therapy. Although very high energies have been achieved with linear accelerators (1) to serve the purposes of investigations in nuclear physics, moderate energies are sufficient for medical purposes. Thus, for x-ray work all the advantages of supervoltage therapy may be realized in the energy range of 3-10 MEV, while technics which make use of direct electron irradiation require energies up to about 30 MEV. On the basis of such considerations, the Stanford medical accelerator was designed to operate at 6 MEV. At this energy, it serves primarily as a source of supervoltage x-rays, and secondarily as a source of low-energy electrons which may be employed in the treatment of superficial skin lesions. The electron applications are currently under development and will not be discussed in this report. Various technical considerations which influenced the final design of this accelerator are described by Ginzton, Mallory, and Kaplan (2). The machine was completed in 1955 and installed at Stanford Hospital. The treatment of patients began in early 1956. It has been customary to operate the accelerator at an energy between 4 and 5 MEV. At 4.2 MEV, the forward intensity of the x-ray beam is 0.38 milliwatts/sq. cm. (corresponding to 65 rads/min. at the maximum of the transition curve in water) for an average electron current of 16 microamperes at the target. Under these conditions, the corresponding x-ray dose distributions are similar to those described by Greene and Tranter (3) and by Murison and Hughes (4). Magnetic analysis of the electron beam indicated that satisfactory operation is obtainable in the range of 2 to 5.5 MEV. Linear accelerators must be operated under pulsed conditions. In the present design, the electron beam is incident on the target in bursts of approximately one microsecond duration, repeated 480 times per second. Thus, the x-ray intensity during the pulse is about 2,000 times higher than the average intensity. This report is intended as a description of the physical characteristics of the machine and the relevant instrumentation and technics that have evolved. What is described here is not to be interpreted as optimum in any sense but rather as a step toward the development of a useful tool in radiation therapy. The Accelerator Since descriptions of the physical and electrical characteristics of linear electron accelerators have already been given (1, 2), only those features which are pertinent to radiotherapeutic applications will be described.