Extended soft X-ray emission spectroscopy: quantitative assessment of emission intensities

Soft X‐ray emission spectroscopy (SXES) in the energy range between 150 eV and 1500 eV has typical attenuation lengths between tens and a few hundred nanometres. In this work the transmission of soft X‐rays in synchrotron‐based SXES has been quantitatively analysed using specially prepared layer samples. The possibility of extending the standard qualitative analysis of SXES by exploiting the information underlying the emission intensity was examined for thin layer structures. Three different experiment series were accomplished with model layer systems based on different sulfur‐containing substrates: (i) MoS₂, (ii) CuInS₂, (iii) Cu(In,Ga)(S,Se)₂. The absorption of the S L_2,3 emission line by ZnO cover layers of up to 80 nm thickness was monitored and compared with theoretical expectations. By comparison with a reference intensity recorded from a bare substrate, the attenuation of the S L_2,3 emission could be used to accurately determine the ZnO overlayer thickness up to a critical thickness, depending on the set‐up and the net S L_2,3 emission intensity. The results from these local energy‐resolved spot measurements were compared with spatially resolved scans of the integral S L_2,3 emission intensity over areas of several mm². In the scan images the attenuation of the S L_2,3 emission intensity clearly reflects the local ZnO layer thickness. From the attenuation the ZnO layer thicknesses were calculated and compared with ellipsometric measurements and were found to be in excellent agreement. These results demonstrate the benefits of a quantitative analysis of SXES, making it an even more powerful tool for examining buried interfaces and for monitoring lateral inhomogeneities.     

β-delayed neutron emission studies

The study of β-delayed neutron emission plays a major role in different fields such as nuclear technology, nuclear astrophysics and nuclear structure. However the quality of the existing experimental data nowadays is not sufficient for the various technical and scientific applications and new high precision measurements are necessary to improve the data bases. One key aspect to the success of these high precission measurements is the use of a very pure ion beam that ensures that only the ion of interest is produced. The combination of the IGISOL mass separator with the JYFLTRAP Penning trap is an excellent tool for this type of measurement because of the ability to deliver isobarically and even isomerically clean beams. Another key feature of the installation is the non-chemical selectivity of the IGISOL ion source which allows measurements in the important region of refractory elements. This paper summarises the β-delayed neutron emission studies that have been carried out at the IGISOL facility with two different neutron detectors based on ³He counters in a polyethylene moderator: the Mainz neutron detector and the BEta deLayEd Neutron detector.     

X-ray emission spectroscopy—part I

Summary of Part I: The detection of X-rays by photographic recording, ionization chambers, proportional counters, scintillation counters, and semiconductor detectors is discussed. The extraordinary improvement in resolution achieved by semiconductor detectors resulted in a new powerful analytical method: detection of characteristic X-rays. Sample excitation, by X-rays, by charged particles produced by accelerators and by radioactive sources, is discussed. Charged particle induced X-ray emission is described within B framework of simple theoretical models. Experimental data on yields of X-rays produced by proton and heavy ion bombardment of different targets are summarized. The cross sections for the production of X-rays in ion-atom collisions are large. This allows the detection of elements present in very small amounts within the target, as well as the measurement of the charge of particles using beam foil spectroscopy.

Part II of this article will describe some applications of X-ray emission spectroscopy in industry, water and air pollution, and in the study of the importance of trace elements in biology and medicine. Sensitivity, background problems, target preparation and data reduction for X-ray emission spectroscopy will be discussed.     

Edge emission of AlxGa1−xN

The photoluminesence in the edge emission region of Al_xGa_1−xN> (0 ≦ x ≦ 0.24) has been studied. The compositional dependence of the band gap was studied and the bowing parameter was determined: b = 0.98 eV. With increasing x the edge emission peak broadens, explanation of the mechanism of which has been attempted.     

Carbon nanotube emitters and field emission triode

Based on our study on field emission from multi-walled carbon nanotubes (MWNTs), we experimentally manufactured field emission display (FED) triode with a MWNTs cold cathode, and demonstrated an excellent performance of MWNTs as field emitters. The measured luminance of the phosphor screens was 1.8 × 103 cd/m2 for green light. The emission is stable with a fluctuation of only 1.5% at an average current of 260 μA.     

Enhanced spontaneous emission factor for microcavity lasers

The microcavity and the influence of nonradiative recombination can control spontaneous emission.An analytic resolution of rate equation is studied for microcavity lasers.The relationship between output prop- erties and structural parameters of multi-quantum wells(MQWs)is obtained.One of the most important consequences of the increased spontaneous emission factor is the reduction of laser threshold.It is found that the characteristic curve of a"thresholdless"laser is strongly nonradiative depopulation-dependent. The light output is increased by the enhanced well number and the reduced width.In particular,there is an optimal well number corresponding to the lowest threshold current density for MQW structure in the microcavity lasers.     

Ultrafast blue light emission from SiC nanowires

Cubic silicon carbide (SiC) nanowires are synthesized in a catalyst-assisted process. The nanowires with diameter of - 40 nm exhibit strong blue light emission at room temperature under ultraviolet (UV) femtosecond laser excitation. The photon energy of peak emission is higher than the energy bandgap of cubic SiC which shows involvement of quantum confinement effect. The ultrafast fluorescence is deconvoluted by Monte-Carlo method. The results show two ultrafast decay processes whose lifetimes are about 26 and 567 ps respectively. The mechanisms of such ultrafast processes are discussed.     

Kβ X-ray emission from He-like ions

Relativistic calculations on the energies and electric dipole rates of K_β X-rays from 1s3p(¹P₁,³P₁)-1s² (¹S₀) transitions for He-like ions in the range Z=14–54 are carried out using multi-configuration Dirac–Fock (MCDF) wave functions in the active space interaction approach. The contributions from Breit interaction and quantum electrodynamics have also been included in the calculation. An attempt has been made to find a scaling expression for Breit energy in terms of Zα .The scaled Breit energies are in good agreement with the earlier accurate relativistic results and this ensures the reliability of our scaling procedure. The behavior of MCDF wavefunctions for a given J in the non-relativistic limit has also been studied. The calculated K_β X-ray energies and rates agree well with other available experimental and theoretical values.     

Pre-equilibrium γ-ray emission in dissipative heavy-ion collisions

-rays are measured in coincidence with the dissipative complex fragments from the³⁵Cl +⁶⁴Ni reaction at 7.7 A MeV. Theoretical -ray coincidence spectra are determined through a fitting procedure using the contribution of the excited fragment statistical -decay calculated by means of the CASCADE code. Whereas the expected statistical spectra fit very well the data in the energy regionE =2 to 8 MeV, above this energy another emission mechanism in addition to the statistical decay has to be considered in order to reproduce the experimental spectra. Simulations based on the Vlasov equation suggest that this emission could come from the decay of dipole strength excited in the intermediate dinuclear system.The authors are greatly indebted with A. Boiano, A. Buccheri, M. Cipriano, F. Pagano and R. Rocco for their assistance during the set up of the experimental apparatus. Dr. J. Girard and the technical staff of the CEA/DAPNIA-DPhN are acknowledged for the valuable operation of the accelerator.     

MeV – proton emission from ultrafast laser-driven microparticles

Propagation of a high intensity (10¹⁹ W/cm²) ultrashort (35 fs) laser pulse through a cloud of water spheres (150 nm diameter) results in hot electron driven proton acceleration up to 1 MeV. It is suggested that during the propagation of the short pulse through the low density wing of the cloud, the leading pulse pedestal is reduced owing to absorption by the preplasma created. Then, the high-intensity peak of the pulse propagates through this underdense plasma and interacts with the high-density inner part of the cloud, which has not been transformed into an underdense plasma so that a sheath acceleration process at each individual microsphere can take place. The observed proton spectra show strong modulations, which are interpreted within the framework of a known fluid-expansion model incorporating two hot-electron populations with significantly different densities and temperatures. PACS 52.50.Jm; 52.38.Kd; 41.75.Jv     

High energy γ-ray emission in heavy-ion collisions

We calculate double-differential cross sections for energetic photon production in intermediate energy nucleus-nucleus collisions. The production mechanism is assumed to be either that of collective bremsstrahlung or that of electromagnetic transitions between time-dependent single-particle states as emerging from a self-consistent treatment of the heavy-ion dynamics in the one-body limit (TDHF). Effects from residual nucleon-nucleon collisions on the collective current are further taken into account via a relaxation ansatz for the single-particle occupation numbers. The total yields for energetic photon production above 50 MeV in the simple limit considered indicate that up to 10% of the experimental cross sections can be attributed to collective bremsstrahlung and electromagnetic transitions.     

The branching ratio ofβ-delayed two-proton emission

The decay of the ⁺-fed isobaric analog state by one- and two-proton emission is calculated in the formalism of compound-nucleus decay. Support is given to the uncorrelated character of the emitted protons in the2p process. The ratio of2p top probabilities is obtained for the isotopes predicted to be2p emitters up to Z=30, i.e.²²Al,^22,23Si,²⁶P,²⁷S,³¹Ar,³⁵Ca,³⁹Ti,⁴³Cr,⁴⁶Mn,^46,47Fe,^49–51Ni, and⁵⁵Zn.     

Tachyonic Cherenkov emission from Jupiterʼs radio electrons

Tachyonic Cherenkov radiation from inertial relativistic electrons in the Jovian radiation belts is studied. The tachyonic modes are coupled to a frequency-dependent permeability tensor and admit a negative mass-square, rendering them superluminal and dispersive. The superluminal radiation field can be cast into Maxwellian form, using 3D field strengths and inductions, and the spectral densities of tachyonic Cherenkov radiation are derived. The negative mass-square gives rise to a longitudinal flux component. A spectral fit to Jupiter?s radio spectrum, inferred from ground-based observations and the Cassini 2001 fly-by, is performed with tachyonic Cherenkov flux densities averaged over a thermal electron population.     

Radio waves and γ-ray emission from astrophysical sources

A mechanism of X- and γ-ray emission by relativistic electrons at interaction with astrophysical objects (maser clouds) is considered and the contribution of this mechanism to the formation of a continuous spectrum and its correlation with radio-wave radiation are investigated. The radiation yield upon deexcitation of a quantum system by an electron exceeds that of “conventional” (i.e., without a change in the quantum-system state) bremsstrahlung at small nuclear charges (Z < 10) and may be about 8% of the total γ-ray intensity. It is shown that in the direction in which the γ-ray intensity increases, one should observe radio waves corresponding to a particular maser source.     

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1-2A GeV

Angular distributions of pious and kaons produced in heavy ion collisions at the low-energy end of high energies （1-2 A GeV） have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.     

Velvet＇s multi-pulsed emission and multi-pulsed electron beams

The velvet electron emission characteristics and beams＇ brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery emission is much stronger than that from the centre. The periphery emission contributes much more to the formation of the cathode plasma than the centre emission, which leads to diode impendence breakdown. The relationship between the cathode plasma expansion and the initial emittance of the cathode is deduced to describe the characteristics of the multi-pulsed vacuum diode. The emittance of the multi-pulsed beams is measured to be less than 1000mm·mrad. The brightness of the electron beams is better than 1× 10^8A/（m·rad）2.     

Radiation emission from the ＂Rhodotron-TT200＂ cavity

In this paper, the X-rays emitted from the Rhodotron-TT200 cavity have been studied in depth. We found that the Bremsstrahlung interaction is the only contribution of X-ray generation important to safety. The X-ray dose rate in the Rhodotron vault is calculated for normal conditions based on MCNP4C results. The presented calculation shows good agreement with the experimental measurements, which consequently confirms the reliability of the calculation for use in shielding design and other safety aspects.     

Phosphorus on platinum — Field electron emission microscopy studies

Phosphorus deposited onto a clean Pt FEM tip (at RT) reacts readily with the emitter surface below 630 K. Compound clusters are formed on top of a coherent compound layer. Cluster formation, growth, and disappearance below 890 K indicate a high compound mobility. The coherent compound layer shows the development of {221} planes, an enlargement of the {110} areas and ring structures around {100}. The coherent compound layer breaks up only upon heating to about 1670 K. The observations are discussed briefly in connection with Pt-phosphide chemistry and P poisoning of Pt surfaces.     

Source mechanism of acoustic emission produced by pitting corrosion

Studies have been made on the source mechanism of acoustic emission produced by pitting corrosion. Methods for identifying pitting corrosion-related AE signals were proposed and the magnitude of surface displacement due to single pitting was estimated. It is concluded that differentiation between background noise and corrosion induced genuine AE signal is possible through using plate wave acoustic emission theory combined with parameter analysis method.