Wide Energy Window Research Articles

Energy activation of adiabatic and nonadiabatic electron transfer

Low-level and two-level approaches to above-barrier reactions are used to establish the borders between adiabatic and nonadiabatic electron transfer to either stable or unstable products. The multiple curve-crossing probability is equal to unity in a narrow ‘‘energy window,’’ just above the barrier, and slowly decreases with energy over it. When the reactants are the Langevin oscillators and the energy dispersion per period is less than the width of energy window, Mel’nikov’s one-level theory is appropriate. Otherwise (at higher friction) it must be replaced by the two-level nonadiabatic theory of Burshtein and Zharikov. The transition from an energy diffusion regime to transition state theory (TST) or perturbation theory results occurs within the Langevin model at much lower friction than within the ‘‘strong collision model’’ considered previously.

Effect of energy resolution on scatter fraction in scintigraphic imaging: Monte Carlo study.

The effect of energy resolution in detector systems on scatter fractions in scintigraphic imaging through Monte Carlo simulation is investigated. A 10-cm Tc-99m line source within a cylindrical water phantom 20 cm in diameter and 20 cm in length was modeled and energy spectra were calculated at three different line source positions. The energy resolution was changed from 8% to 16% FWHM at 140 keV and a symmetrical energy window width was varied from 8% to 23% on the photopeak of 140 keV in energy spectra corresponding to each energy resolution. The relationship between the scatter fraction and the symmetrical energy window width, and the relationship between the scatter fraction and the primary counts were presented for all energy resolutions investigated. Furthermore, the effect of the asymmetrical energy window on reducing the scatter fraction was also studied and compared with the narrow symmetrical energy window. The results quantitatively showed that improved energy resolution can considerably decrease the scatter fraction with a narrow symmetrical energy window or an asymmetrical energy window without significant primary count-loss compared to that obtained with lower quality energy resolution. The asymmetrical energy window could reduce scatter fraction as compared with the narrow symmetrical energy window when the same number of primary counts was required for both energy windows. Knowing the relationship between the scatter fraction and the primary counts is important in scintigraphic imaging to select the optimum energy window corresponding to the energy resolution.

Background problem in electron-energy-loss spectroscopy.

At large scattering angle the background formation in electron-energy-loss spectroscopy is determined by elastic-inelastic scattering events. The suitability of the usual background fitting ${\mathit{AE}}^{\mathrm{\ensuremath{-}}\mathit{r}}$ is critically investigated as a function of specimen thickness, collection angle, and width of energy window.

Investigation and use of plasmon losses in energy‐filtering transmission electron microscopy

SUMMARYThe electron spectroscopic imaging (ESI), diffraction (ESD) and different types of electron energy‐loss spectroscopy (EELS) modes in an energy‐filtering transmission electron microscope can all be used for the investigation and analytical use of plasmon losses. Shifts of plasmon losses caused by differences in composition can be detected with an accuracy of 0.1 eV by parallel‐recorded EELS (PEELS). The dispersion of plasmon losses and the cut‐off angle θc can be observed by angle‐dispersive EELS and by recording spectra at different scattering angles θ. ESD patterns with a selected energy window width of 1 eV enable the dispersion and its anisotropy to be imaged by characteristic intensity distributions between the primary beam and the first Bragg diffracted beams. The ESI mode can be used for the selective imaging of precipitates and for the investigation of the excitation volume of plasmons in small particles.

Influence of secondary ion energy distributions on SIMS matrix ion intensities and relative sensitivity factors in the system GaAs/GaAlAs

SIMS investigations are presented on erosion rates, suited matrix ions for layer identification in layer systems of GaAs and GaAlAs depending on the Al concentration and the acceptable secondary ion energies using O 2 + and Ar + primary ions and positive secondary ions. The development of relative sensitivity factors of the doping elements Mg, Si, Cr, Zn, Ge, Sn is also measured depending on the Al concentration and the accepted secondary ion energy using O 2 + bombardment. The SIMS measurements are shown to be very sensitive to the choice of position and width of the ion energy window. The investigations show partially considerable enhancement of the low-energy portion of the secondary ion energy distribution with increasing Al content, typical for this chemical element, especially between O and 20 at % Al. The higher-energy portion of the energy distributions is much less influenced by the Al content.

Scatter detection in SPECT imaging: dependence on source depth, energy, and energy window

The authors examine the dependence of the scatter fraction on source depth, the energy window width and the emitted photon energy, Monte Carlo calculations are presented of scatter fractions for a line source of activity at eleven depths in a water-filled cylinder acquired in seven energy window widths for each of five primary photon energies corresponding to radionuclides commonly used in nuclear medicine studies.

A Macroscopic Study of the Neutron, Gamma- and X-Ray Emissivity in the Frascati Plasma Focus

Experiments were carried out in the neutron-optimized mode of the plasma focus operation with small electrode diameters and condenser bank energies of 250, 390, and 490 kJ. The time sequence of the emitted radiation (neutron and gamma) was realized by the time-of-flight (TOF) method using an NE-102A plastic scintillator and silicon detectors viewing X rays from the plasma exclusively. The detectors were operated in the wide-energy window mode. Special attention was given to the interpretation of neutron TOF traces and their comparison with the absorption analysis and previously measured spectra by nuclear plates. Average values are discussed simultaneously with the results of representative single shots. It was found that two (something more) neutron bursts are typical and, in each case, are accompanied by simultaneous hard X rays. The maxima of emissivities coincide with the dI/dt maximum. A theoretical analysis of the results reveals the existence of long time-confined streams of fast electrons and deuterons (effective-energy -- 80keV) with evidence of their slowing down.

Crystal analyser type quasielastic spectrometers using the pulsed cold neutron source

Two crystal analyser type quasielastic neutron spectrometers, a conventional resolution device with high efficiency, and a high resolution one with a wide energy window, have been installed at a spallation pulsed cold neutron source (a 20 K methane moderator). A data reduction program using a technique of statistical data analysis has also been developed. These spectrometers combined with the data reduction program have demonstrated their usefulness in profile analysis studies for low energy diffusive phenomena in molecular liquids, polymers and other materials.

Characterization of excimer laser annealing of ion implanted Si

An evaluation of a XeCl excimer laser for the laser processing of Si is reported. The annealing quality of ion-implantation damage, as measured by the crystalline perfection of the regrown layer and by p-n junction characteristics, is similar to that obtained with ruby or Nd:YAG lasers. However, the wide energy window between annealing and surface damage, the flat smooth surface obtained after laser irradiation, the capability of providing deep surface melting, and other features, indicate that XeCl and perhaps other excimer lasers is nearly ideal for semiconductor processing.

Optimum ‘windows’ in quantitative energy dispersive analysis

AbstractOptimum energy window widths are derived using random counting statistics for use in quantitative energy dispersive analysis over a wide range of peak‐to‐background ratios. It is shown that a peak energy window width equal to the full width as half maximum gives good results for most practical cases.

Performance of Silver Zeolite in a Radioiodine Monitor

Measurement were made of the interaction of 8Kr, 133Xe, CH3I (131I) and I2 (131I) with various silver zeolites and activated charcoals under varying relative humidities and temperatures. Results show silver zeolite has significantly less interaction with noble gases and high adsorption efficiencies for CH3I making it superior to charcoal for airborne radioiodine monitoring. The penetration of airborne iodine activity into the silver zeolite filter bed was also examined. CH3I penetrated slightly deeper than I2 at the same air flow velocity; however, at 17.4 feet per minute, no more than 5% of the iodine activity in either form penetrated deeper than 1 cm into the filter bed. The sensitivity of the iodine-131 activity detection system was found to be approximately 2.5% (1% = 2.22 x 104 counts per minute/μCi) at the 364 Kev photopeak with a 100 Kev energy window width.