Determination of elements in some lichens growing in Giresun and Ordu province (Turkey) using energy dispersive X-ray fluorescence spectrometry

The concentration of five different elements in six lichens species of different regions in Giresun and Ordu (Turkey) was determined using the energy dispersive X-ray fluorescence method. A radioisotope excited X-ray fluorescence analysis using the method of multiple standard addition is applied to the elemental analysis of lichens. An annular 50 mCi ²⁴¹Am radioactive source and an annular 50 mCi ⁵⁵Fe radioactive source were used for excitation of characteristic K X-rays. An Si(Li)detector which has a 147 eV full-width at half-maximum for 5.9 keV photons was used for intensity measurements. A qualitative analysis of spectral peaks showed that the samples contained potassium, calcium, titanium, iron, and barium.     

Design and performance evaluation of SDD based X-ray spectrometer for future planetary exploration

Silicon Drift Detector (SDD) based X-ray spectrometer has been developed for obtaining the elemental composition of unknown samples by detecting fluorescent X-rays in the energy region 1–25 keV by a non-destructive process. The use of new technology X-ray detector provides good energy resolution for detecting the elements separated with ～150 eV apart. Here we present the design of a complete X-ray spectrometer intended for use in the future space-born experiment. The low energy threshold of <1 keV and the energy resolution of ～150 eV at 5.9 keV, as measured from the system is comparable to the standard spectrometers available off-the-shelf. We evaluated the system performance for different signal peaking time, as well as for different input count rates and show that the performance remains stable for incident count rate up to 20,000 counts per second. We have also carried out a ‘proof of concept’ experiment of measuring fluorescent X-ray spectrum from various standard XRF samples from the USGS catalog irradiated by the laboratory X-ray source ²⁴¹Am with 1 mCi activity. It is shown that intensities of various characteristic X-ray lines are well correlated with the respective elemental concentrations. A specific effort has been made while designing the developed X-ray spectrometer to use electronic components which are available in space grade so that the same electronic design can be used in the upcoming planetary missions with appropriate mechanical packaging.     

Mechanically driven millimeter source of nanosecond X-ray pulses

The emission of nanosecond pulses of ≈20 keV photons having a total energy of GeVs which are generated by peeling millimeter wide strips of pressure sensitive adhesive (PSA) tape in a partial pressure of air (≈10⁻³ Torr) is demonstrated. The X-ray spectrum is similar to that obtained by peeling much wider bands of PSA, implying that the characteristic length for the sequence of processes that govern this phenomenon is less than 1 mm. These experiments demonstrate that MEMS-type X-ray generators are technologically feasible.     

Mn-doped (Ba,Y)Fe12O19 hexaferrites: Crystal structure and oxidation states of Mn and Fe

We have fabricated Ba_0.95Y_0.05Fe_12-xMn_xO₁₉ samples with large Mn-doping amounts of x = 4 and 6, using the mechanical milling and heat treatment. X-ray diffraction analysis indicated the samples crystallized in the M-type hexaferrite structure. The Mn doping caused the modification, shift and broadening of some characteristic phonon-vibration modes, which were recorded by Raman spectroscopy. This is due to an incorporation of Mn ions into the M-type structure that disorders the periodic lattice and changes symmetry. Basing on X-ray absorption spectroscopy, we have found Fe in all samples stable with an oxidation state 3+ (Fe³⁺). Though Mn²⁺ and Mn³⁺ ions coexist, the concentration of Mn²⁺ in x = 4 is larger than that in x = 6. The analysis of Fourier-transform spectra have demonstrated the replacement of Mn^2+,3+ ions for Fe³⁺ in the M-type structure. The sites of Mn^2+,3+ ions in this structure have been discussed.     

Competing nucleation mechanisms and growth of InAsSbP quantum dots and nano-pits on the InAs(100) surface

InAsSbP quantum dots (QDs) and nano-pits (NPs) are grown on a InAs(100) surface by liquid phase epitaxy (LPE). Their morphology, dimensions and distribution density are investigated by high resolution scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and total energy calculations. QDs average density ranges from 5 to 7 × 10⁹ cm^?2, with heights and widths having a Gaussian distribution with sizes from 5 nm to 15 nm and 10 nm to 40 nm respectively. The average pits density is (2–6) × 10¹⁰ cm^?2 with dimensions ranging from 5–30 nm in width and depth. We also find a shift in the absorption edge towards the longer wavelengths together with broadening towards shorter wavelengths indicating that these QDs and lateral overgrown nano-pits are grown at the n-InAs/p-InAsSbP heterojunction interface. Together with total energy calculations, the results indicate that lattice mismatch ratio plays a central role in the growth of these strain-induced nano-objects.     

Applicability of an X-ray and gamma-ray portable spectrometer for activity measurement of environmental soil samples

This paper presents a study on the applicability of a commercial X-ray and gamma-ray portable spectrometer (Rover) for in situ gamma-ray spectrometry. This portable spectrometer consists of a 3 × 3 × 1 mm (CdTe) Cadmium Telluride detector and a 30 × 30 mm [NaI (Tl)] Sodium Iodide detector. The radioactive sources used were ²⁴¹Am, ¹³³Ba, ¹⁵²Eu and ¹³⁷Cs tablet type, sealed with aluminum and polyethylene, as well as soil samples contaminated with ¹³⁷Cs. With the aid of these radioactive sources, this study determined the efficiency curve for both detectors. In addition, measurements were carried out to identify the minimum detectable activity (MDA) for both detectors, using time acquisition change ranging from 900 s to 138 h, depending on which detector was utilized and the sample distance. The results for the tablet-type sources were as follows: The MDA for the CdTe detector, while positioned 4.15 cm from the ¹³⁷Cs source, was 15 kBq and 6 kBq for energy lines 32 keV and 661.65 keV, respectively. However, when the distance between the source and detector was 100 cm, the 661.65 keV line presented a MDA of 68 kBq. Results for the soil samples were as follows: Using the CdTe detector, positioned 4.15 cm from the source, the MDA was 73 Bq for the ¹³⁷Cs 32 keV line. In relation to the ⁷Be soil samples, the MDA was 301 Bq when the detector was 4.15 cm from the source. Using the NaI (Tl) detector to analyze the ¹³⁷Cs 661.65 keV line, the MDA was 8 kBq when the detector was 100 cm from the tablet-type source. For the soil sample containing ¹³⁷Cs, the MDA was 7.4 Bq when the source was 2.8 cm from the NaI (Tl) detector. For those samples containing ⁷Be, and measured at the same distance (2.8 cm), the MDA was of 9.6 Bq. Based on the minimum detected activities obtained for both detectors, it is concluded that the in situ gamma-ray spectrometric system used to quantify soil sample activities with ¹³⁷Cs and ⁷Be is only appropriate when those activities are around one or more orders of magnitude larger than the usual radioactivity levels found in the environment. Even though it is a commercialized machine, the Rover system’s manufacturer does not provide the information cited in this abstract.     

Cavitation-assisted decontamination of yttria from graphite of different densities

Yttria coated graphite crucibles are widely used to handle molten refractory and radioactive metals like uranium and plutonium. However, the coated layer suffers damages like cracking and peeling off owing to thermal cycles. As a result, removal of the yttria layer from the graphite surface is essential to ensure reuse of the crucible and minimization of radioactive waste. The present work investigates intensified dissolution of yttria from the coated graphite samples using ultrasound as a non-destructive decontamination technique to recycle the graphite substrate. The optimum conditions established for maximum dissolution were 8 M as acid strength, frequency of 30 kHz, temperature of 45 °C and power density of 8 W cm⁻² that resulted in maximum dissolution of 52% in 30 min. Use of an oxidant H₂O₂ to the acid, did not yield any improvement in the dissolution kinetics, instead, increased oxidation of the graphite substrate was observed, leading to the anomalous weight gain of the graphite substrate despite surface erosion. Effect of ultrasound on the dissolution was pronounced, with almost a threefold increase compared to dissolution performed under silent conditions. Rates of dissolution of yttria from the substrate of different densities and pore size distribution were also studied. The dissolution was slowest from graphite of density 1.82 g cm⁻³ as the pore size distribution was conducive to accommodate the yttria particles. The dissolution in nitric acid followed ash layer diffusion controlled kinetics. The study has demonstrated the efficacy of application of ultrasound for accelerated decontamination of graphite substrates.     

Characterization of the channel walls roughness in photonic crystal fibers

We present electron microscope (FEI NanoSEM) and atomic force microscopy measurements of surface roughness in nanochannels in photonic crystal fibers (PCF). A method was invented to cleave the PCF along the axis without damaging the surface structure in the nanochannels allowing us to characterize the morphology of the nanochannels in the PCF. A multi-wall carbon nanotube mounted onto commercial AFM probes and super sharp silicon non-contact mode AFM probes were used to characterize the wall roughness in the nanochannels. The roughness is shown to have a Gaussian distribution, and has an amplitude smaller than 0.5 nm. The height–height correlation function is an exponential correlation function with an autocorrelation length of 13 nm, and 27 nm corresponding with scan sizes of 200×100 nm², and 1600×200 nm², respectively.     

Radiation damage in soft X-ray microscopy

The rates of chemical transformation by radiation damage of polystyrene (PS), poly(methyl methacrylate) (PMMA), and fibrinogen (Fg) in a X-ray photoemission electron microscope (X-PEEM) and in a scanning transmission X-ray microscope (STXM) have been measured quantitatively using synchrotron radiation. As part of the method of dose evaluation in X-PEEM, the characteristic (1/e) sampling depth of X-PEEM for polystyrene in the C 1s region was measured to be 4 ± 1 nm. Critical doses for chemical change as monitored by changes in the X-ray absorption spectra are 80 (12), 280 (40) and 1230 (180) MGy (1 MGy = 6.242*ρ eV/nm³, where ρ is the polymer density in g/cm³) at 300 eV photon energy for PMMA, Fg and PS, respectively. The critical dose for each material is comparable in X-PEEM and STXM and the values cited are thus the mean of the values determined by X-PEEM and STXM. C 1s, N 1s and O 1s spectroscopy of the damaged materials is used to gain insight into the chemical changes that soft X-rays induce in these materials.     

Measurements of neutron radiation and induced radioactivity for the new medical linear accelerator,the Varian TrueBeam

Contemporary linear accelerators applied in radiotherapy generate X-ray and electron beams with energies up to 20 MeV. Such high-energy therapeutic beams induce undesirable photonuclear (γ,n) and electronuclear (e,e'n) reactions in which neutrons and radioisotopes are produced. The originated neutron can also induce reactions such as simple capture, (n,γ), reactions that produce radioisotopes. In this work measurements of the non-therapeutic neutrons and the induced gamma radiation were carried out in the vicinity of a new medical accelerator, namely the Varian TrueBeam. The TrueBeam is a new generation Varian medical linac making it possible to generate the X-ray beams with a dose rate higher than in the case of the previous models by Varian. This work was performed for the X-ray beams with nominal potentials of 10 MV (flattening filter free), 15 MV and 20 MV, and for a 22 MeV electron beam. The neutron measurements were performed by means of a helium chamber and the induced activity method. The identification of radioisotopes produced during emission of the therapeutic beams was based on measurements of the energy spectra of gammas emitted in decays of the produced nuclei. The gamma energy spectra were measured with the use of the high-purity germanium detector. The correlation between the neutron field and the mode and nominal potential was observed. The strongest neutron fluence of 3.1 × 10⁶ cm⁻² Gy⁻¹ and 2.0 × 10⁶ cm⁻² Gy⁻¹ for the thermal and resonance energies, respectively, was measured during emission of the 20 MV X-ray beam. The thermal and resonance neutron fluence measured for the 15 MV X-rays was somewhat less, at 1.1 × 10⁶ cm⁻² Gy⁻¹ for thermal neutrons and 6.7 × 10⁵ cm⁻² Gy⁻¹ for resonance neutrons. The thermal and resonance neutron fluences were smallest for the 10 MV FFF beam and the 22 MeV electron beam and were around two orders of magnitude smaller than those of the 20 MV X-ray beam. This work has shown that the neutron reactions are dominant because of relatively high cross sections for many elements used in the accelerator construction. The detailed analysis of the measured spectra made it possible to identify 11 radioisotopes induced during TrueBeam delivery. In this work the following radioisotopes were identified: ⁵⁶Mn, ¹²²Sb, ¹²⁴Sb, ¹³¹Ba, ⁸²Br, ⁵⁷Ni, ⁵⁷Co, ⁵¹Cr, ¹⁸⁷W, ²⁴Na and ³⁸Cl.     

Structural phase transformations in annealed cubic ZnS nanocrystals

The structural changes of cubic ZnS (cZnS) nanocrystals (NCs) doped with 0.2 at.% Mn²⁺ pulse annealed in vacuum and in air, up to 500 °C, were investigated by multifrequency electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples, prepared by a surfactant (Tween20)-assisted liquid–liquid reaction at pH = 6, consist of NCs with a tight size distribution around 3 nm and high crystallinity self-assembled into a stable mesoporous structure. The EPR spectra of the as prepared samples contain only the characteristic lines of the substitutional Mn²⁺(I) centers. No spectra from Mn²⁺ ions localized in (hydro)oxidized regions of the NCs surface were observed. The absence of such a surface layer could explain the stability of the cubic (sphalerite) structure observed by XRD and TEM in the investigated cZnS:Mn NCs annealed in vacuum up to 500 °C. The observation of the cubic-hexagonal transformation for the same NCs annealed in air supports the role of such layer in promoting this structural transformation. The narrowing of the EPR spectral lines above 200 °C with the increase in the average size of the cZnS:Mn crystallites was observed. The effect was more pronounced for the sample annealed in air. EPR also revealed the formation of minute amounts of substitutional Mn²⁺-type centers in a hexagonal ZnO structure at T ~ 300 °C, corresponding to the early stages of the thermally induced oxidation of the cZnS:Mn NCs.     

Analysis of some elements in three Chrysolina (Coleoptera, Chrysomelidae) species by EDXRF spectrometry

In this investigation, the concentration levels of potassium, calcium, iron, nickel and cadmium for three Chrysolina species were measured in the region of Erzurum (Turkey) located at latitude 40°17′ north and longitude 41°17′ east. The concentrations measured by energy dispersive X-ray fluorescence (EDXRF) spectrometry were analysed. Photons of 59.5 keV and 5.9 keV emitted, respectively, by an annular ²⁴¹Am and ⁵⁵Fe radioactive source were used to excite the characteristic X-rays of various elements present in the insect samples. These results are presented and discussed in this paper.     

Electrical conductivity and NMR studies in paraelastic phase of Tl2SeO4

We have carried out the electrical conductivity and NMR measurements and investigated the characteristic features of the electrical conductivity in a paraelastic phase of Tl₂SeO₄. It was found from electrical conductivity measurement that the activation energy in the paraelastic phase (above T_c(= 661 K)) is 0.98 eV. We also found that ²⁰⁵Tl-NMR line width drastically decreases above T_c and becomes approximately 0.5 Gauss. This result indicates that in the paraelastic phase the mobile Tl ions exist. Moreover this result is consistent with the existence of the anomalously large hopping motion of Tl ions observed in X-ray diffraction measurement. Furthermore the activation energy estimated from the motional narrowing of ²⁰⁵Tl-NMR absorption line is 0.92 eV and is in agreement with that obtained from the conductivity measurement. From these results, it is deduced that the mobile Tl ions play an important role in the appearance of electrical conductivity in the paraelastic phase.     

Synchrotron-based investigation of iron precipitation in multicrystalline silicon

We report on investigations of the precipitation of iron in block-cast multicrystalline silicon using the techniques of X-ray beam induced current, X-ray fluorescence microscopy and X-ray absorption microspectroscopy. The samples studied were intentionally contaminated with iron and annealed at temperatures between 850 and 1050 ^°C. Annealing at 950 ^°C was found to lead to well detectable iron precipitation inside the grains and at grain boundaries. Small only iron clusters were detected after the 850 ^°C anneal while no iron clusters were found after the 1050 ^°C treatment. X-ray absorption near edge structure analyses of the iron clusters revealed mostly iron silicide and in one case iron oxide. Under the given condition at the beamline, the detection sensitivity for iron was estimated to be 4×10⁷ atoms, corresponding to a spherical FeSi₂ particle of 40 nm radius.     

Femtosecond X-rays from relativistic electrons: new tools for probing structural dynamics

Femtosecond X-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with X-ray pulses to investigate structural dynamics at the atomic scale on the fundamental time scale of an atomic vibrational period (∼100 fs). This new research area depends critically on the development of suitable femtosecond X-ray sources with the appropriate flux (ph/(s·0.1% BW)), brightness (ph/(s·mm²·mrad²·0.1% BW)), and tunability for demanding optical/X-ray pump probe experiments. In this paper we review recently demonstrated techniques for generating femtosecond X-rays via interaction between femtosecond laser pulses and relativistic electron beams. We give an overview of a novel femtosecond X-ray source that is proposed based on a linear accelerator combined with X-ray pulse compression.     

EPR Investigation of Radical-Production Cross Sections for Sucrose and L-alanine Irradiated with X-rays and Heavy-ions

Using electron paramagnetic resonance (EPR), we investigated stable radical-production cross sections (σ) of sucrose and L-alanine radicals produced by heavy-ion irradiations with various linear energy transfers (LET). The heavy-ion irradiation results were compared with those of X-ray irradiation at the same dose. The EPR signal areas for the two compounds showed a linear relation with the absorbed dose, as well as a logarithmic correlation with the LET. Further analysis was carried out for the radical-production cross section, which showed that stable radicals of the two compounds were produced through collisions of several particles with a single molecule. The relative σ value of sucrose for C ion irradiation was (1.29 ± 0.64) × 10⁻¹² μm². The σ value of alanine for C ion irradiation was (6.83 ± 0.42) × 10⁻¹³ μm². Considering the structural molecular sizes of sucrose and alanine, the σ values are similar. In addition, a comparison of the EPR results for the C ions and X-rays at 50 Gy dose was made. Sucrose spin concentrations produced by C ions at the LET value of 13.1 keV/μm and X-rays were similar unlike alanine. Thus, the noble EPR results with X-ray and heavy-ion irradiations imply that sucrose can be useful as a radiation indicator.     

Crystal growth,luminescence and scintillation properties of Eu2+:CeBr3 crystals

Eu²⁺:CeBr₃ crystals were grown by vertical Bridgman growth method and slight aliovalent doping of Eu²⁺ in the CeBr₃ crystal did not change the crystal structure. The X-ray stimulated luminescence, photoluminescence, decay kinetics and scintillation properties were investigated at room temperature. The X-ray stimulated luminescence spectra exhibited wide broad emission bands from 3.54 eV to 2.95 eV in the Eu²⁺:CeBr₃ crystal with high content of 620 ppm of Eu²⁺, which were the overlap of the emission bands ascribed to 5d → 4f transition of Ce³⁺ and 4f⁶5 d¹ → 4f⁷ transition of Eu²⁺, respectively. When the content of Eu²⁺ was decreased to 70 ppm, another emission band centered at 2.29 eV was observed. The photoluminescence spectra showed the energy transfer from Ce³⁺ to Eu²⁺. This decreased the Ce³⁺ emission intensity but enhanced the Eu²⁺ emission intensity. The photoluminescence decay time of Ce³⁺ emission decreased from 14 ns to 10 ns when the content of Eu²⁺ increased from 70 ppm to 620 ppm. The decay time of the emission of 525 nm did not change with the excitation wavelength and Eu²⁺ content, which could be assigned to the excitons that were bound on Eu²⁺ related centers. The light output of the Eu:CeBr₃ crystal under the excitation of ²⁴¹Am radioactive source was less than 20.2% of Tl:NaI crystal.     

The structure of compositionally constrained zinc-ferrite spinel nanoparticles

ZnFe₂O₄ bulk material shows a normal-spinel structure and a closely defined composition at Zn²⁺/Fe³⁺ ≅ 0.5. However, the composition of zinc ferrite, prepared as nanoparticles, can be varied in a broad range without losing the single-phase spinel structure. In this article, structural mechanisms enabling this non-stoichiometry were studied using the X-ray absorption fine structure (EXAFS) in combination with X-ray diffractometry (XRD), transmission electron microscopy (TEM), and magnetic measurements. Nanoparticles with a narrow size distribution were synthesized using co-precipitation in water-in-oil microemulsions. First, the structure of the stoichiometric zinc-ferrite nanoparticles was studied in dependence of their size and the annealing temperature. EXAFS analysis showed that the degree of inversion x (as defined in the compound formula (Zn_1 − x Fe _x )[Fe_2 − x Zn _x ]O₄, with round and square brackets representing the tetrahedral and octahedral sites, respectively) increased with decreasing nanoparticles size. The structure of the stoichiometric nanoparticles and the nanoparticles of comparable size displaying Zn/Fe ratio of 0.2 (Fe-rich) and 0.7 (Zn-rich) were then compared. Analysis showed that the non-stoichiometry is structurally compensated predominantly in the core of the nanoparticle by the adjusted distribution of Zn and Fe ions over the two sublattices of the spinel structure.     

A comparative study of the ionic keV X-ray line emission from plasma produced by the femtosecond,picosecond and nanosecond duration laser pulses

We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 10⁴ J cm^− 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 10¹⁷ W cm^− 2 for the 45 fs pulses and 6.2 × 10¹⁴ W cm^− 2 for the 25 ps pulses are much higher than 5 × 10¹² W cm^− 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma.     

Ferromagnetism in Zn1−xCrxTe (x = 0.05, 0.15) films grown on GaAs(1 0 0) substrate

Zn_1−xCr_xTe (x = 0.05, 0.15) films were grown on GaAs(1 0 0) substrate by thermal evaporation method. X-ray diffraction analysis showed the presence of ZnCrTe phase without any secondary phase. The surface was analyzed by high resolution magnetic force microscope and profile measurements showed orientation of magnetic domains in the range of 0.5–2 nm with increase of Cr content. Magnetic moment–magnetic field measurements showed a characteristic hysteresis loop even at room temperature. The Curie temperature was estimated to be greater than 300 K. From the electron spin resonance spectra, the valence state of Cr in ZnTe was found to be +2 with d² electronic configuration. Hall effect study was done at room temperature and the result showed the presence of p-type charge carriers and hole concentration was found to increase from 5.95 × 10¹² to 6.7 × 10¹² m⁻³ when Cr content increases. We deduce the origin of ferromagnetic behavior based on the observed experimental results.