Search

A high-resolution electron spectrometer has been constructed for the study of clean metal surfaces and their interactions with gases. In its present form it is most suitable for the study of evaporated films but may also be used for ribbons, single crystals, or powders. Electron spectra induced by three sources, X-ray, vacuum ultraviolet, or electron impact, may be recorded sequentially. Electron energy analysis is normally performed by settin the analyzer (10 cm radius, hemispherical) to pass electrons of a fixed energy and applying a scanning retarding potential to the sample. The limiting instrument absolute resolution is about 25 meV FWHM at 5 eV analyzing energy, as judged by an He I gaseous argon spectrum. Resolution can be traded for sensitivity by analyzing at higher electron energies (up to 100 eV), or by means of an external slit-width adjustment mechanism. The spectrometer carri a preparation chamber which has a variety of demountable sample preparation, cleaning, and reaction monitoring devices. Spectra from gold, silver, and

The construction of an electron spectrometer using a 80 mm 2 × × 3 mm cooled Si(Li) detector has been described. The system resolutions (fwhm) for 115, 194 and 624 keV electrons were found to be 0.88, 1.06 and 1.50 keV, respectively. The resolution (fwhm) for 5.8 MeV α-particles was found to be 12.0 keV. The Si(Li) detector did not show any deterioration in performance after several warming and cooling cycles over a period of two years. The thickness of the Si dead layer on the detector face was estimated from the energy loss of low-energy electrons and was found to be 0.6 μm. The spectrometer described here can be used for the measurement of electron lines above 20 keV energy. Also because of its simple design the spectrometer can be used for α−e − and γ−e − coincidence experiments.

The room temperature adsorption of CO on polycrystalline Molybdenum is used to compare X-ray induced and electron impact induced electron spectroscopy techniques. The system was considered suitable because it is known that monolayer adsorption, at the surface only, takes place. The instrument used was 200 electron spectrometer fitted with Mg Kα and electron sources, and a rotatable sample probe. The relative and absolute ESCA and Auger peak intensi compared and a preliminary investigation was made of the effect on surface sensitivity of changing the angle of emission of the detected electrons. Sma impact beam effects were noted through the beam current is so small that there is no speed advantage over X-ray impact.

The features of the spherical analyzer with and without pre-retardation are compared. The results are applicable to other types of spectrometers as, e.g., the cylindrical analyzer and the cylindrical mirror.

A velocity spectrum is obtained by dispersing the photoelectrons with a uniform electrostatic field; it is recorded on an electronographic film with the help of an electronic camera. To each point of the plate correspond definite values of the tangential and normal velocities of photoelectrons. The angular and energetic distribution N(W, φ) is calculated from the density of the electronographic plate. We hereby show the first structures obtained from thin films of gold.

The performance of a single-gap electron spectrometer for in-beam isomeric lifetime measurements on the University of Manitoba Cyclotron is described. Conversion electrons following (p, x n) reactions are detected in delayed coincidence relative to the 28 MHz proton beam bursts. An overall resolving time of 770 ps fwhm is achieved for 345 keV electrons produced in the 197 Au(p,2ne − ) 196 Hg reaction. A determination of the half-life of the 1911 keV isomeric state in 194 Hg yields T 1 2 = (4.46±0.11) ns .

The level scheme of75Se has been studied through the75As (p, n) reaction at proton energies from 1.5 to 5.0 MeV.γ-ray and internal conversion electron measurements were made using NaI (T1) and Ge(Li) detectors and a six-gap electron spectrometer. A proportional counter and a thin window NaI(T1) detector were used to detectγ-rays with energies less than 30 keV. The level scheme has been established by observing the thresholds of variousγ-rays and byγ-γ and e−-γ coincidence measurements. New levels at 133.0, 293.2, 790.0, 953.0, 1020.8, 1184.3, 1198.5 and 1258.2 keV not observed in earlier (p, n) studies have been established. Conversion coefficients of most of the low-lying transitions have been determined. Angular distributions of some of theγ-rays were also measured and compared with the statistical model calculations. DefiniteJ π assignments have been made to most of the low-lying levels. Life-times of the 112.1, 133.0, 286.7 and 293.2 keV levels have been measured to be 0.69±0.12, 5.3±0.6, 1.35±0.15 and 31±2 nsec respectively. The reduced transition probabilities for various low-lying transitions have been determined and compared with recent calculations. The 1/2− and 9/2+ levels hitherto unknown in this nucleus has been identified. The structure of the low-lying levels is discussed in terms of the existing models.

This is a preliminary report of the first satellite observations that have been made of the intensities and energy spectra of the bremsstrahlung >50 keV produced in the atmosphere by intense widespread precipitations of energetic electrons from the outer radiation belt. The measurements afford the opportunity to investigate nearly simultaneously the energetic electron behavior on a worldwide scale during magnetic disturbances. With such a technique, one may study different features of the precipitation processes than those covered by satellite-borne particle detectors, which can provide more detailed particle information in a local region but without simultaneous measurements from many satellites can provide worldwide particle precipitation information only from long-term statistical studies. The observations are made with a 50-cm³ Ge(Li) gamma ray spectrometer that was launched aboard the spin-stabilized satellite 1972–076B into a nearly circular polar orbit at 750-km altitude on October 2, 1972. Correlative measurements of precipitating electrons are also made with an energetic electron spectrometer on board the same satellite. The longitude and hence local time extents of the precipitations are derived by least square fitting techniques from the gamma ray spectrometer responses at various spin angle orientations and satellite locations. The observations indicate the occurrence of nearly simultaneous precipitations over a wide range of local times. Significant variations occur in the intensity versus local time, but in the limited number of cases studied to date the intensities near noon are generally greater than those in the early morning hours.

A spectrometer system designed to measure the time‐dependent kinetic energy of electrons from high current pulsed relativistic beam accelerators is described. The spectrometer, consisting of a three‐element vacuum Compton diode, is simple, rugged, and self‐driving. Calibration data are presented covering the energy range of 150 keV to 16 MeV. Applications and limitations of the spectrometer are discussed.

A low‐energy, high resolution, electron impact spectrometer with a molecular beam target has been constructed and used to study the electronic energy levels of acetone vapor. Similar spectra were also taken with a second electron spectrometer having a static gas target. Both sets of spectra are essentially identical and show the expected singlet states at 4.37, 6.35, and 7.45 eV, the first triplet state at 4.16 eV, and a very broad second triplet process from 5.3 to 6.1 eV with an intensity maximum at 5.88 eV. Attempts to resolve vibrational structure in the latter band were unsuccessful, even though vibrational spacings of 0.14 eV were easily resolved elsewhere in the spectrum.

A model is developed in which a magnetic field aligned potential difference is assumed to accelerate electrons downward into the atmosphere. It is pointed out that the upgoing backscattered electrons produced by this electron beam may process insufficient kinetic energy to overcome the hypothetical potential difference. These electrons will be reflected downward to appear as members of a precipitating electron population. A numerical model was constructed in order to describe the total precipitating electron flux in terms of a primary accelerated beam and backscatter from the atmosphere. It is pointed out that many features that appear in the model beam are observed in the auroral electron beam as well. An example of an auroral beam, measured by Frank and Ackerson (1971), is compared favorably with a model electron beam formed by a parallel potential.

Some basic electron optics and computational techniques useful in electron optical design are reviewed and applied to the design of a constant-background electron transmission spectrometer.

A method for determination of the relative efficiency of Si(Li) electron spectrometers with the sources 180m Hf, 207 Bi, and 210 At is described. New measurements of some relative γ-ray (photon) intensities in 180m Hf and 207 Bi are given. Electron line intensities for all three sources, calculated from the decay schemes, γ-ray intensities, and theoretical internal conversion coefficients, are tabulated.

The requirements for applying Auger electron spectroscopy (AES) are relatively simple: (i) a vacuum environment to maintain a stable, surface condition during the measurement interval and to avoid electron-gas collisions; (ii) excitation sources to induce Auger transitions in surface atoms; (iii) an electron spectrometer; and (iv) specimens sufficiently small to fit into the vacuum system and of such geometry that the spot of interest can be properly located with respect to the spectrometer. The applications of AES discussed herein are depth profiling of the chemical composition in the near-surface region, investigation of chemical environment of elements in surface regions, determination of changes in the chemistry of surface atoms, quantitative surface analysis, investigation of grain-boundary segregation and its effect on embrittlement and subsequent fracture. Auger spectra are shown for a fractured Ti-6Al-4V specimen, a Rene-alloy-specimen surface, an alumina particle imbedded in a Rene alloy, and an ...

An electrostatic electron spectrometer for energies up to 10 keV, consisting of two coaxial cylinders, is described together with its data acquisition system. The spectrometer permits free access to both source and detector region, the distance between source (or detector) and spectrometer being 1 cm. This new design property is made possible by introducing potential shaping fringe plates of novel design. The spectrometer transmission or resolution can be adapted to the specific experimental needs by exchanging apertures. The spectrometer is protected from external fields by a magnetic shield integrated into its design.

Scattering of the radiation emitted in a radioactive decay at the constructional components of a magnetic spectrometer will give rise to a background which usually is not eliminated by coincidence techniques. The background spectrum depends upon the features of the decay under investigation, the instrumental settings and the design parameters of the spectrometer. We investigated origin and intensity of various types of background signals observed in a magnetic lens spectrometer. Quantitative representative results are given which can provide an order of magnitude estimate for the background intensity to be expected in a certain decay. Significant background intensities are caused by γ-radiation as well as by electrons emitted in the decay. It was found that scattered conversion electrons can give rise to sharp structures in the apparent electron spectrum, which are comparable to or even narrower than the instrumental resolution. It is shown by which counter measures the various types of backgrounds can be minimized.

All spectrometers although they reject spurious signals to some extent have extraneous components in their “line profiles”. If each line exhibits a low intensity tail, a continuum composed of such lines will be found to be erroneously high in the region where the tails “pile up”. For optical and mass spectrometers this is usually not a problem because their dynamic ranges are short. However, this is not the case for some electron spectrometers, particularly for the Keplertron, which has a dynamic range from 1 eV to 40 000 eV. To determine the Keplertron's response, line profiles were obtained with an electron gun to provide a mono-energetic source variable from 50 eV to 10 000 eV. All line profiles have the same general shape — a large, central peak and a low energy tail which is a factor of 1 000 to 5 000 lower than the central peak. Calculations show that if a hypothetical flat 1 MeV beta ray spectrum were studied, that the spurious tails would produce a 30% extraneous increase in apparent electron flux from the source at 1 keV and a 300% enhancement at 100 eV. The distortion is negligible, however, for electron slowing down spectra which have an E−1 shape below 10 keV.

In the summer of 1971 we conducted new measurements of the primary electron spectrum from 1 to 20 Gev with our electron spectrometer telescope at Fort Churchill. This telescope has been calibrated by using electrons and pions of 0.5–15 Gev at Slac (Stanford Linear Accelerator) in early 1971 and again in 1972. The differential primary electron spectrum over the energy range 3–20 Gev is given by dj/dE = 100/E3±0.2 el/m² ster sec Gev, the integral spectrum by J(E) = 50/E2±0.2. These intensities are considerably lower than many earlier measurements above ∼5 Gev. It is observed that many showers have anomalous lateral distributions as determined in our telescope and must be rejected. This directly leads to the lower intensities. Our calibration results suggest that these events are due to interactions of high-energy protons. Our measured primary electron spectrum is uncomfortably close to that calculated for secondary electrons produced by the interaction of cosmic ray nuclei with interstellar hydrogen in the galaxy, and therefore the question of the origin of the high-energy electrons is reopened. The problem of the age of cosmic ray electrons must also be reexamined if our measured spectrum is found to extend to still higher energies.

A magnetic lens spectrometer has been built and tested. New features include (a) alignment with the earth's magnetic field to eliminate the deflection of the focal spot by this field, (b) use of a segmented coil to achieve a substantial reduction in spherical aberration, and (c) use of cathode rays for alignment, calibration, and for measurement of the aberration. Completely automatic operation has been achieved. Special attention is given to the effects of source backing and to focusing conditions for electrons in the very low energy region.

A total absorption lead glass Cerenkov counter to be used as γ‐ray and electron spectrometer in the 1–10 Gev region is described. The calibration of the counter with monoenergetic electrons shows its response to be linear at least up to 14 Gev. The pulse‐height spread improves with increasing energy and it is better than 10% (full width at half‐height) for energies above 5 Gev.

A detailed study has been made of the 3s3p6np 1P and 3s3p6nd 1D autoionizing resonances in Ar using a high resolution electron spectrometer. Positions and widths of the features are presented and compared with the results of other workers and with theory.

An apparatus is described, with which, for the first time, the spectra of Augere-lectrons and of X-rays, produced by the impact of electrons, were measured simultaneously. The electron spectrometer was a magnetic 180°-spectrometer with a half-width of 0·5%. The X-ray spectrometer was a NaJ-crystal with a photomultiplier. The electron- and the X-rays were produced in metallic foils of a thickness of 50 A by the impact of 55-keV-electrons. The knownK-fluorescence-yields of copper and selenium were used to determine the various yields for theL-shells of gold. TheL-fluorescence-yields areωL1=0·08±0·01;ωL2=0·26±0·03;ωL3=0·24±0·02.

The asymmetry of low-energy positrons produced in μ+ decay has been measured in a hydrogen bubble chamber which was calibrated as a low-energy electron spectrometer. A fit to the expression 1+A(x) cosθ gives the valuesA(0.03

A spectrometer for analyzing photons of energies extending up to several Bev has been constructed and used successfully. This instrument essentially consists of a cylinder of glass, 12‐in. diam and 14‐in. long containing 52% of PbO, viewed by four 5‐in. diam photomultipliers. High‐energy photons incident along the spectrometer axis produce electron showers in the transparent high‐Z glass. The total Cerenkov radiation emitted by these electrons and detected by the phototubes is nearly proportional to the energy of the incident photon, from 50 Mev to at least 1.4 Bev. The spectrometer has been calibrated over this range of photon energies by the pulses produced by electrons of the same energies. Above 200 Mev the measured energy resolution of the spectrometer is 30% and is approximately independent of energy. For elimination of incident charged particles during the analysis of γ rays the spectrometer is operated in coincidence with a preceding photon‐identifying counter system.

The design, construction and performance of a double focusing electron spectrometer are described. The spectrometer has a mean radius of 30 cm, and a maximum transmission of 5% of 4π, at a resolution of 1.5%. Resolutions of 0.07% have been obtained at a transmission of 0.5% of 4π with a source 0.020 inches wide. Three separate criteria of optimum performance have been studied experimentally; the elimination of aberrations associated with φ z the elimination of aberrations associated with φ r , and an intermediate focusing in which the φ z and φ r aberrations are equal and overlap. The performance of this spectrometer under the first of these three criteria is described in detail.

The design and construction of precision current regulators is simplified by the use of commercially available operational amplifiers. Their method of use is described and an example is given of a regulator used with an electron spectrometer, where the regulation obtained was 0.01%. It is felt that the use of operational amplifiers offers a great convenience to the physics laboratory.

A new type of retarding potential difference electron spectrometer using spherical grids is described. The unique feature of the analyzer is a post monochromator section which selectively collects electrons passing the retarding grids with minimum kinetic energy. Factors affecting the resolution of the analyzer are discussed and a comparison with several other spectrometers operating in the resolution range of 0.05% is presented. An application to x‐ray photoelectron spectroscopy is presented.

The results obtained in a previous paper for generalized oscillator strengths in potassium vapour have been re-examined. The angular resolution of the crossed-beam electron spectrometer used for the measurements has been improved and a correction applied for the residual finite angular resolution of the instrument. In addition to potassium, electron energy loss spectra for sodium at 405, 505, 675 and 1005 ev incident electron kinetic energies have been obtained. Absolute generalized oscillator strengths have been derived by normalizing the resonance transition to the optical oscillator strength. For potassium the reduced matrix element (4 2Spr2p5 2S) was found to be 43 A.U. ± 20%, and the transition probability A(3 2D -> 4 2S) found to be 310 s-1 ± 20%. For sodium the reduced matrix elements for the transitions 3 2S -> 4 2S, 5 2S and 6 2S were found to be 33 A.U. ± 15%, 12 A.U. ± 20% and 75 A.U. ± 20%, respectively, and the transition probability A(3 2D -> 3 2S) found to be 690 s-1 ± 10%.

The calibration of an electrostatic deflection, auroral particle spectrometer, which uses bare electron multipliers for detectors, is described. The spectrometer measures the fluxes of both electrons and protons in the energy range 10 to 10 000 eV. An attempt is made to minimize the uncertainty in the measurement of the absolute particle flux to which such instruments are prone. The detection of electrons and protons by electron multipliers is investigated as a function of energy and flux of the particles, and for different values of the multiplier gain.

The phenomena of ion trapping in electron beams are studied experimentally. For a tubular electron beam the total trapped ion charge equals that of the electron charge if no opening of the trap occurs by any negative potential electrode. When a second electron beam is introduced along the axis of the tubular beam, very high ion densities can be established, because the slow electrons created by ionizing collisions of the axial electron beam can neutralize the ionic charge on the axis.

An electron spectrometer which employs double focusing electrostatic plates is described. The photoelectron spectra obtained by bombarding methane, silane, germane, methyl fluoride, difluoromethane, and trifluoromethane with 21.22‐eV photons are presented. The experimental ionization energies are compared with theoretical and other experimental data, and molecular‐orbital assignments are made for the energy values obtained. Broad double maximum bands were observed in the case of methane, silane, and germane and are discussed in terms of Jahn–Teller distortion for the positive ions. Possible correlation of the methane spectrum with interstellar space data is also discussed.

Energies and intensities of conversion electrons and gamma-rays from the decay of 195 Au have been measured with a π √2 electron spectrometer and a Si(Li) detector. The 30.94 keV transition was found to be M1 + (0.045 ± 0.015)% E2 and the 98.84 keV transition was found to be M1 + (1.77 ± 0.23)% E2. The corresponding B (E2) and B (M1) values are fitted into a systematic study of these quantities and compared to theoretical predictions.

We describe the construction and performance of a new electron spectrometer for analysis of low kinetic energy electrons, 0–2000 eV. The design of the analyzer is based on computer calculations and combines many favorable properties of both the retarding and the deflection energy analyzer. The energy analyzer consists of a set of electrodes with cylindrical symmetry and a planar retarding field grid followed by an electrode system with postmonochromatic action. Therefore a differential spectrum is obtained directly. The performance of the analyzer is discussed in terms of resolution, sensitivity, luminosity, and signal‐to‐background. The resolution achieved is 0.5%, with a resolution of 30 meV, making it possible to resolve and study electronic vibrational levels in atoms and molecules. A few spectra of nitrogen and argon are shown as representative of the performance of the new analyzer.

The total and partial internal conversion coefficients of the 31 keV, 99 keV and 130 keV transitions in 195 Pt were measured with a magnetic solenoid electron spectrometer, scintillation and Ge(Li) detectors. The spectrometer transmission and the efficiencies of the gamma-ray detectors were experimentally determined with calibrated reference sources. Corrections to the electron line intensities arising from scattering in the source backing and in the source itself were determined from the analysis of the continuous β-spectrum of 63 Ni sources of various thicknesses evaporated on backings of various thicknesses. The coefficients of the 99 keV transition α K = 5.8±0.5 and α = 6.9±0.5 are in excellent agreement with the previous Mossbauer and gamma spectroscopy results of Harris et al . The partial conversion coefficient ratios of the 31 keV and 99 keV M1 transitions are about 10 % larger than the theoretical calculations of Hager and Seltzer.

The decays of 6.7 min 179mW and 38 min 179W have been studied by means of high resolution γ-ray and electron spectroscopy using Ge(Li) and Si(Li) detectors, a broad-range transport solenoid electron spectrometer and γ-γ coincidences with Ge(Li) detectors. The decay of 38 min 179W occurs by a fast beta transition (logft 4.6) and by a first-forbidden beta transition (logft 6.9) followed by a 30.7 keV and by a 133.9 keV γ-transition, respectively. The [521] 1 2 − 6.7 min 179mW decays mainly by an isomeric transition of 221.5 keV (M3) and a competing 101.6 keV (E4)-120.1 (E2) keV cascade to the 179W ground state. A small fraction of the decay of the 6.7 min isomer is observed to proceed by beta transitions to levels in 179Ta. The results are interpreted in terms of the Nilsson model and the following intrinsic proton states are proposed in 179Ta: [404]if 7 2 + giound state; [514]if 9 2 − 30.67 keV; [402]if 5 2 + 238.7 keV; [411]if 1 2 + 520.4 keV; and [541]if 5 2 − , K = 1 2 at 741.5 keV. The [541] if 1 2 − band is observed to have approximately the same large decoupling parameter (a > 4) as has been found in 173,175Lu.

An electrostatic electron spectrometer for energies between 1 and 50 keV has been designed. The instrument uses two plane retarding fields and two electrostatic lenses. The lenses have been optimized with a computer program. The calculated energy resolution is 0.2% for a source area of 6 cm2 and a transmission of 5%.

The spectral distributions of electrons ejected from plane slabs of compact human bone and Lucite have been measured by a magnetic electron spectrometer at various emerging angles less than 70 deg. for 150–300 kVp X rays. Calculations based on the measurements have provided data for the mean energy and the effective range of secondary electrons. The results have a bearing on the problem of the absorbed dose in soft tissue at a bone-tissue interface.

A spectrometer composed of deflecting magnets and magnetic quadrupoles is described which is designed to analyze particles scattered in the angular range 8°–35° and at incident energies up to 6 GeV. A momentum discrimination between 0.2% and 0.7%, depending on the scattering angle, has been achieved. The performance of the spectrometer for the scattering of 5.275 GeV electrons from protons at 12.5° is described.

A simple homogeneous-field magnetic prism spectrometer is described for use below the camera chamber of a conventional transmission electron microscope. The prism is designed for point-to-point focusing from the exit pupil of the electron microscope to the exit slit of the spectrometer. Energy spectra are scanned by varying the accelerating voltage to minimize chromatic effects in the microscope. Scanning coils are used to deflect an image or a diffraction pattern across an area-selecting aperture which also serves as the aperture stop for the spectrometer. A phase-sensitive periodic differential integrator is used to record the output from the scintillation counter detector.

A magnetic Compton electron spectrometer, to be used in the energy range 0.2 to 4.0 MeV, is described. The instrument is calibrated and used to measure thin-target bremsstrahlung of aluminium and gold foils, the incident electron beam having an energy of 3.5 MeV. Experimental results are compared to theory and existing results.

Electrons accelerated by voltages from 80 kv to 225 kv passed through a thin homogeneous foil of polycrystalline gold and formed a diffraction pattern on a fluorescent screen. Through a hole in the screen, various rays of the diffracted beam were made in turn to fall on a second diffracting foil similar to the first. The second diffraction pattern was obtained on a photographic plate and examined for any asymmetry that might be caused by polarization of the electron beam. After certain asymmetries in the apparatus were corrected, no asymmetry was found in the diffraction pattern. By interposing a vane for a given fraction of the time of exposure over part of the plate, a partial calibration of the plate could be obtained directly. It was estimated that if there was any asymmetry at all, it was certainly not above 10 percent and probably not above 5. From this result and the observations of other workers at voltages from 100 kv down, it seems safe to conclude that diffraction is wholly, or largely, ineffective in polarizing electrons with energies at any rate below 225 kv. This conclusion may be at variance with those of Rupp and Rupp and Szilard on double scattering and on scattering and diffraction of an electron beam. The relation of these different experiments is discussed.