Recent Developments in Txrf of Light Elements

1997 ◽  
pp. 771-779 ◽  
Author(s):  
Christina Streli ◽  
V. Bauer ◽  
P. Wobrauschek
Keyword(s):  
Light Elements ◽  
Recent Developments

scholarly journals NUCLEAR REACTIONS IN HOT ASTROPHYSICAL PLASMAS WITH T > 1010 K

2012 ◽  
Vol 21 (01) ◽  
pp. 1250009 ◽  
Author(s):  
ERVIN KAFEXHIU ◽  
FELIX AHARONIAN ◽  
GABRIELA S. VILA
Keyword(s):  
Gamma Ray ◽  
Nuclear Reactions ◽  
Prompt Gamma ◽  
Theoretical Studies ◽  
Light Elements ◽  
Computational Power ◽  
Astrophysical Plasmas ◽  
Recent Developments ◽  
Γ Ray ◽  
Data Banks

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperatures T ≥1010 K has been recognized for more than thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power have not previously allowed detailed theoretical studies. Recent developments in these areas make it timely to conduct comprehensive studies on the nuclear properties of very hot plasmas formed around compact relativistic objects such as black holes and neutron stars. Such studies are of great interest in the context of scientific programs of future low-energy cosmic γ-ray spectrometry. In this work, using the publicly available code TALYS, we have built a large nuclear network relevant for temperatures exceeding 1010 K. We have studied the evolution of the chemical composition and accompanying prompt gamma-ray emission of such high-temperature plasmas. We present the results on the abundances of light elements D, T, 3 He , 4 He , 6 Li , 7 Li , 9 Be , 10 B , 11 B , and briefly discuss their implications on the astrophysical abundances of these elements.

scholarly journals On the Origin of the Light Elements (D, 3He, 4He and 7Li)

1987 ◽  
Vol 124 ◽  
pp. 89-117 ◽  
Author(s):  
Jean Audouze
Keyword(s):  
Phase Transitions ◽  
High Energy ◽  
Galactic Evolution ◽  
Light Elements ◽  
Canonical Models ◽  
Hadron Phase ◽  
Baryonic Density ◽  
Recent Developments ◽  
Quark Nuggets ◽  
The Universe

The abundances of the very light elements (D, 3He, 4He and 7Li) constitute indeed one of the most powerful constraints in cosmology: they are known to fix very interesting limits on the baryonic density of the Universe and on the maximum number of neutrino (lepton) families in the frame of the simplest canonical models. Given the importance of these predictions, these models should be analysed very cautiously at the light of recent developments in the observations of these elements. In order to make the simplest models consistent with the observations, it is argued that a thorough destruction of D should occur during the galactic evolution. Moreover this review deals also with some models invoking the possible existence of massive unstable neutrinos, gravitinos or photinos which would decay into high energy photons or of quark nuggets which could be created during the quark-hadron phase transitions. Such models have been designed in an attempt to overcome the limitation on the Universe density coming from these abundance determinations. Although the simple canonical models are especially attractive such models cannot be disregarded.

Recent Developments in Txrf of Light Elements

1995 ◽  
Vol 39 ◽  
pp. 771-779 ◽  
Author(s):  
Christina Streli ◽  
V. Bauer ◽  
P. Wobrauschek
Keyword(s):  
Absorption Edge ◽  
Detection Efficiency ◽  
Fluorescence Analysis ◽  
Total Reflection ◽  
Low Energy ◽  
X Rays ◽  
Light Elements ◽  
Energy Dispersive Analysis ◽  
X Ray ◽  
Recent Developments

Total Reflection X-ray Fluorescence Analysis (TXRF) has been proved to be well suited for the energy dispersive analysis of light elements, as B, C, N, O, F, Na, Mg,.,. using a special spectrometer. It is equipped with a Ge(HP) detector offering a sufficient detection efficiency from 180 eV upwards. The obtainable detection limits especially of the light elements are mainly influenced by the excitation source, which should provide a large number of photons with an energy near the K-absorption edge of these elements (from 200 eV upwards). Commercially available X-ray tubes do not offer characteristic X-rays in that range. In former experiments a windowless X-ray tube was built to prevent the low energy X-rays from being attenuated in the Be window. Experiments have been performed using Cu as anode material.

scholarly journals Interstitial and substitutional light elements in transition metals for heterogeneous catalysis

2021 ◽  
Author(s):  
Tianyi Chen ◽  
Christopher Foo ◽  
Shik Chi Edman Tsang
Keyword(s):  
Heterogeneous Catalysis ◽  
Transition Metals ◽  
Light Elements ◽  
Recent Developments ◽  
Catalytic Applications

TOC summarises some recent developments in synthesis, characterisation and catalytic applications of light elements doped to transition metals presented in this article.

Detection and Quantification Problems in the Analysis of Light Elements With UTW Detectors

1990 ◽  
Vol 48 (2) ◽  
pp. 464-465
Author(s):  
Gilles L’Espérance ◽  
Gianluigi Botton ◽  
Mario Caron
Keyword(s):  
Qualitative Analysis ◽  
Energy Resolution ◽  
Energy Dispersive Spectrometry ◽  
Biological Materials ◽  
Energy Dispersive ◽  
Routine Analysis ◽  
Light Elements ◽  
Recent Developments ◽  
Qualitative Analyses ◽  
Detection And Quantification

Recent developments in windowless (WL) or ultra-thin window (UTW) detectors, improved energy resolution, larger angles of collection (0.15-0.2 sterad), higher voltages (200-400 kV) make energy dispersive spectrometry more attractive for the analysis of low Z elements down to beryllium (Ref. 1 and Fig. 1). It lends itself to faster, more routine analysis and offers in many cases the possibility of carrying out qualitative analysis for a wider range of materials thickness. It has, however, generally been recognised to have lower sensitivities than EELS except for some elements in biological materials. Also, UTW analysis have been restricted to qualitative analyses, largely due to the large absorption even for relatively thin samples.This paper presents results that can typically be achieved with both SEM and TEM’s, difficulties in quantifying the data and the sensitivity that can be expected.The detectors (Link LZ-4 and Link LZ-5) on both our SEM (JEOL 840) and TEM (JEOL 2000FX) have a resolution of ≈ 134 ev at 5.9 kev and allow the detection of boron from pure B with the peak well resolved from the background and a peak/valley ration of 12.

Trends in Electron Energy Loss Spectroscopy

1977 ◽  
Vol 35 ◽  
pp. 228-229
Author(s):  
C. Colliex ◽  
P. Trebbia
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Materials Science ◽  
Analytical Technique ◽  
Recent Developments ◽  
Quantitative Results ◽  
Electron Microscopes ◽  
Electron Energy Loss ◽  
Primary Electrons

The physical foundations for the use of electron energy loss spectroscopy towards analytical purposes, seem now rather well established and have been extensively discussed through recent publications. In this brief review we intend only to mention most recent developments in this field, which became available to our knowledge. We derive also some lines of discussion to define more clearly the limits of this analytical technique in materials science problems.The spectral information carried in both low ( 0<ΔE<100eV ) and high ( >100eV ) energy regions of the loss spectrum, is capable to provide quantitative results. Spectrometers have therefore been designed to work with all kinds of electron microscopes and to cover large energy ranges for the detection of inelastically scattered electrons (for instance the L-edge of molybdenum at 2500eV has been measured by van Zuylen with primary electrons of 80 kV). It is rather easy to fix a post-specimen magnetic optics on a STEM, but Crewe has recently underlined that great care should be devoted to optimize the collecting power and the energy resolution of the whole system.

Filaments and membranes in the mitotic apparatus

1983 ◽  
Vol 41 ◽  
pp. 544-547
Author(s):  
Kent McDonald
Keyword(s):  
Intermediate Filaments ◽  
Mitotic Spindle ◽  
Mitotic Apparatus ◽  
Light Microscope Level ◽  
Microtubule Associated Proteins ◽  
Recent Developments ◽  
Associated Proteins ◽  
Force Generator ◽  
Spindle Function ◽  
Antibody Technology

At the light microscope level the recent developments and interest in antibody technology have permitted the localization of certain non-microtubule proteins within the mitotic spindle, e.g., calmodulin, actin, intermediate filaments, protein kinases and various microtubule associated proteins. Also, the use of fluorescent probes like chlorotetracycline suggest the presence of membranes in the spindle. Localization of non-microtubule structures in the spindle at the EM level has been less rewarding. Some mitosis researchers, e.g., Rarer, have maintained that actin is involved in mitosis movements though the bulk of evidence argues against this interpretation. Others suggest that a microtrabecular network such as found in chromatophore granule movement might be a possible force generator but there is little evidence for or against this view. At the level of regulation of spindle function, Harris and more recently Hepler have argued for the importance of studying spindle membranes. Hepler also believes that membranes might play a structural or mechanical role in moving chromosomes.

Scattering-angle dependence of signal/background ratio of inner-shell electron excitation loss in EELS

1983 ◽  
Vol 41 ◽  
pp. 390-391
Author(s):  
T. Oikawa ◽  
M. Inoue ◽  
T. Honda ◽  
Y. Kokubo
Keyword(s):  
Energy Loss ◽  
Electron Excitation ◽  
Heavy Elements ◽  
Background Intensity ◽  
Light Elements ◽  
Energy Analyzer ◽  
High Background ◽  
Scattering Angle ◽  
Angle Dependence ◽  
Shell Electron

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.

Software pattern recognition applied to nanodiffraction patterns from a STEM instrument

1986 ◽  
Vol 44 ◽  
pp. 694-695
Author(s):  
G.Y. Fan ◽  
J.M. Cowley
Keyword(s):  
Image Processing ◽  
Pattern Recognition ◽  
Computer Software ◽  
Processing System ◽  
Light Level ◽  
Host Computer ◽  
Low Light ◽  
Image Processing System ◽  
Recent Developments ◽  
On Line

In recent developments, the ASU HB5 has been modified so that the timing, positioning, and scanning of the finely focused electron probe can be entirely controlled by a host computer. This made the asynchronized handshake possible between the HB5 STEM and the image processing system which consists of host computer (PDP 11/34), DeAnza image processor (IP 5000) which is interfaced with a low-light level TV camera, array processor (AP 400) and various peripheral devices. This greatly facilitates the pattern recognition technique initiated by Monosmith and Cowley. Software called NANHB5 is under development which, instead of employing a set of photo-diodes to detect strong spots on a TV screen, uses various software techniques including on-line fast Fourier transform (FFT) to recognize patterns of greater complexity, taking advantage of the sophistication of our image processing system and the flexibility of computer software.

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