• Volume 76, Issue 2

February 2011,   pages  189-371

• Foreword

• X-ray spectrometry for preventive conservation of cultural heritage

Analytical chemistry does play a key role in the chemical characterization of the environment and it appears that X-ray spectrometry, in its many forms, is one of the most relevant analytical techniques in preventive conservation, as it is in cultural heritage research in general. X-ray spectrometry has indeed been the method of choice for the characterization of the inorganic composition of atmospheric aerosols, for a long time.

We have, over the last decade, intensively used various forms of X-ray spectrometry, viz., mostly energy-dispersive X-ray ﬂuorescence, e.g. with polarized high-energy beam excitation, and automated electron probe X-ray microanalysis, together with other techniques, to identify particle types and their sources in indoor environments, including museums, while gaseous indoor pollutants were assessed using passive diffusion samplers. In each case, both bulk aerosols and individual aerosol particles were studied. For microanalysis of single particles, we have investigated a dozen techniques, but for wide, real-life applications, automated electron probe X-ray microanalysis is the most rewarding.

We have ﬁrst studied atmospheric aerosols in and around the Correr Museum in Venice, many other museums in Austria, Japan and England, and in the caves with prehistoric rock paintings in Altamira, Spain. Very recently, measurements were done in the Metropolitan Museum of Art in New York and the Wawel Castle in Cracow, in Italian and Polish mountain churches, in a number of museums in Belgium and the Netherlands, and in cathedrals with medieval stained glass windows. In the Correr museum, it appeared that the particles most threatening for the Bellini paintings were released by the deteriorating plaster renderings, and this could be avoided by simply improving the rendering on the museum walls. In the Wawel Castle, outdoor pollution particles, like ﬁne soot from diesel trafﬁc, entering via leaks in the windows and doors, and also street-deicing salts and coal burning pollution particles, brought in by visitors, mostly in winter, were found to be most worrisome.

Urgent questions that are not solved at this moment pertain to the deposition processes from the atmosphere to the cultural heritage items, the critical surface interactions that take place on these items, and the establishment of suitable particle concentration standards.

• Total reﬂection X-ray ﬂuorescence and energy-dispersive X-ray ﬂuorescence characterizations of nuclear materials

Nuclear energy is one of the clean options of electricity generation for the betterment of human life. India has an ambitious program for such electricity generation using different types of nuclear reactors. The safe and efﬁcient generation of electricity from these reactors requires quality control of different nuclear materials, e.g. nuclear fuel, structural materials, coolant, moderators etc. These nuclear materials have to undergo strict quality control and should have different speciﬁed parameters for their use in nuclear reactors. The concentration of major and trace elements present in these materials should be within speciﬁed limits. For such chemical quality control of these materials, major and trace elemental analytical techniques are required. Since some of these materials are radioactive, the ideal chemical characterization techniques should have multielement analytical capability, should require very less sample (micrograms level) for analysis so that the radioactive waste generated, and radiation exposure to the detector and operator are minimum. Total reﬂection X-ray ﬂuorescence (TXRF) and energy dispersive X-ray ﬂuorescence (EDXRF) with improved features, e.g. application of ﬁlters, secondary target and instrumental geometry require very small amount of sample and thus can be suitably used for the characterization of nuclear materials mainly for the determination of elements at trace and major concentration levels. In Fuel Chemistry Division, TXRF analytical methods have been developed for trace element determinations in uranium and thorium oxides, chlorine determination in nuclear fuel and cladding materials, sulphur in uranium, uranium in sea water etc. Similarly, EDXRF analytical methods with radiation ﬁlters (to reduce background) and improved sample preapartion techniques, e.g. fusion bead and taking samples in the form of solution on ﬁlter papers have been used for developing analytical methods for the determination of U and Th in their mixed matrices, Cd in uranium etc. Some ofthese studies have been reported in this paper.

• New applications of the good old wavelength-dispersive X-ray fluorescence

Wavelength-dispersive X-ray fluorescence can be characterized by its advantages and drawbacks. Unbeaten spectral resolution in a range below 5 keV, good operational stability, excellent ability of making averaged analysis, and good presentation of peak shape which gives the basis for the chemical speciation are the advantages. Among the drawbacks, the following are important: system with sequential analysis of particular elements, low output of energy supplied to the device, and great cost of instrument which can be amortized only in routine operations. In routine geological and environmental analyses, the WD-XRF performs better than other simpler instrumental or wet techniques. WD-XRF is continuously improved, by applying new multilayer interference mirrors (MIM) for detection and quantiﬁcation of very light elements. Bad spectral resolution of MIM noted earlier is now improved by tailoring their shape to the shape of gratings. The progress in the long wavelength spectral region joined with efﬁcient and precise wavelength resolution systems enables the application of WD-XRF for speciation analysis. In another effort, XRF spectrometry is treated as a tool for obtaining quantitative basis for the judgement on Linnaean systematic classiﬁcation of plants and opens the ﬁeld to a new discipline – quantitative biology.

• Inﬂuence of near-edge processes in the elemental analysis using X-ray emission-based techniques

The near-edge processes, such as X-ray absorption ﬁne structure (XAFS) andresonant Raman scattering (RRS), are not incorporated in the available theoretical attenuation coefﬁcients, which are known to be reliable at energies away from the shell/subshell ionization thresholds of the attenuator element. Theoretical coefﬁcients are generally used to estimate matrix corrections in routine quantitative elemental analysis based on various X-ray emission techniques. A tabulation of characteristic X-ray energies across the periodic table is provided where those X-rays are expected to alter the attenuation coefﬁcients due to XAFS from a particular shell/subshell of the attenuator element. The inﬂuence of XAFS to the attenuation coefﬁcient depends upon the atomic environment and the photoelectron wave vector, i.e., difference in energies of incident X-ray and the shell/subshell ionization threshold of the attenuator element. Further, the XAFS at a shell/subshell will signiﬁcantly alter the total attenuation coefﬁcient if the jump ratio at that shell/subshell is large, e.g., the K shell, L3 subshell and M$_5$ subshell. The tabulations can be considered as guidelines so as to know what can be expected due to XAFS in typical photon-induced X-ray emission spectrometry.

• Energy-dispersive X-ray fluorescence – A tool for interdisciplinary research

Trace elements have been at the focus of attention for decades with considerable emphasis on their role in biology and biomedical sciences, environmental sciences, geology, archaeology and material sciences. They comprise a large number of elements, some having essential physiological functions, whereas others are toxic, mutagenic or carcinogenic. A few even have antiproliferative and anticarciniogenic properties. The advent of various instrumental techniques and sophisticated instrumentations has made their detection to very low limits possible, making this a very important multidisciplinary study. Among these techniques the energy-dispersive X-ray ﬂuorescence (EDXRF) technique is being widely used for trace element detection in various ﬁelds of science. Keeping the importance of trace elements in mind, the Kolkata centre of UGC-DAE Consortium for Scientiﬁc Research initiated several research schemes in different ﬁelds of trace element research using various techniques, EDXRF being one of the main techniques. A Xenemetrix (erstwhile Jordan Valley) EX 3600 EDXRF spectrometer is being used to carry out the research. This presentation aims to highlight some of the very recent applications of EDXRF in the study of the role of trace elements in pre-cancerous tissues, medicinal plants and also in some environmental studies.

• In vivo applications of X-ray ﬂuorescence in human subjects

X-ray ﬂuorescence has been used to measure several elements noninvasively within living human subjects. Some description is given of the constraints imposed by this rather unusual form of analysis together with a brief listing indicating the range of elements for which such analyses have been developed. Measurements of two elements are then presented in more detail. Lead is measured in bone and has become a well-established tool in continuing research into the long term effects of lead. Strontium is also measured in bone and, although presently not in widespread use, offers the potential for essential information in the study of the reported beneﬁts of strontium supplementation.

• Synchrotron-based X-ray ﬂuorescence, imaging and elemental mapping from biological samples

The present study utilized the new hard X-ray microspectroscopy beamline facility, X27A, available at NSLS, BNL, USA, for elemental mapping. This facility provided the primary beam in a small spot of the order of $\sim 10 \mu m$, for focussing. With this spatial resolution and high ﬂux throughput, the synchrotron-based X-ray ﬂuorescent intensities for Mn, Fe, Zn, Cr, Ti and Cu were measured using a liquid-nitrogen-cooled 13-element energy-dispersive high-purity germanium detector. The sample is scanned in a `step-and-repeat’ mode for fast elemental mapping measurements and generated elemental maps at 8, 10 and 12 keV, from a small animal shell (snail). The accumulated trace elements, from these biological samples, in small areas have been identiﬁed. Analysis of the small areas will be better suited to establish the physiology of metals in speciﬁc structures like small animal shell and the distribution of other elements.

• Synchrotron radiation X-ray microﬂuorescence techniques and biological applications

Synchrotron X-ray imaging systems with ﬂuorescence techniques was developed for biomedical researches in Brazilian Synchrotron Laboratory. An X-ray ﬂuorescence microtomography system was implemented to analyse human prostate and breast samples and an X-ray microﬂuorescence system was implemented to study bone sites of human and animal samples with and without bone disorders.

• Quantitative energy-dispersive electron probe X-ray microanalysis for single-particle analysis and its application for characterizing atmospheric aerosol particles

An energy-dispersive electron probe X-ray microanalysis (ED-EPMA) technique using an energy-dispersive X-ray detector with an ultra-thin window, designated as low-Z particle EPMA, has been developed. The low-Z particle EPMA allows the quantitative determination of concentrations of low-Z elements such as C, N and O, as well as higher-Z elements that can be analysed by conventional ED-EPMA. The quantitative determination of low-Z elements (using full Monte Carlo simulations, from the electron impact to the X-ray detection) in individual particles has improved the applicability of single-particle analysis, especially in atmospheric environmental aerosol research; many environmentally important atmospheric particles, e.g. sulphates, nitrates, ammonium and carbonaceous particles, contain low-Z elements. To demonstrate its practical applicability, the application of the low-Z particle EPMA for the characterization of Asian Dust, urban and subway aerosol particles is shown herein. In addition, it is demonstrated that the Monte Carlo calculation can also be applied in a quantitative single-particle analysis using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectrometry (EDX), showing that the technique is useful and reliable for the characterization of submicron aerosol particles

• X-ray fluorescence activities at Saha Institute of Nuclear Physics, India

This paper covers different aspects related to X-ray ﬂuorescence activities at Saha Institute of Nuclear Physics, Kolkata, India. In its ﬁrst part, experiments on basic physical problems are illustrated and in the second part, some applications related to X-ray ﬂuorescence are discussed.

• Portable energy-dispersive X-ray ﬂuorescence equipment for the analysis of cultural heritage

Energy-dispersive X-ray ﬂuorescence (EDXRF) especially in its portable version, generally characterized by a small X-ray tube and a Si-PIN or Si-drift detector is particularly useful to analyse works of art. EDXRF technique is nondestructive, noninvasive and multielemental. A variety of works, such as paintings of all types (including frescos and illuminated manuscripts), bronzes and brasses, gold alloys, silver alloys, ceramics, porcelains and faiences, papers, ink, stones of all types (marbles, obsidians etc.), stamps, etc. can be studied using a portable EDXRF equipment. In this paper, examples are given for analysis of the works of art with a portable EDXRF equipment.

• An overview of quantiﬁcation methods in energy-dispersive X-ray ﬂuorescence analysis

This paper reviews the major factors inﬂuencing the accuracy of the energy-dispersive X-ray ﬂuorescence (EDXRF) analysis including physical and chemical matrix effects (resulting from particle size, surface irregularity, mineralogy, moisture, absorption and enhancement) as well as the correction procedures with emphasis on the analysis of unprepared samples. Quantiﬁcation methods for thin samples, samples with intermediate thickness and thick samples are presented including fundamental parameter methods, inﬂuence coefﬁcient algorithms, empirical coefﬁcient algorithms and quantiﬁcation methods based on scattered primary radiation. Quality control procedures are also reviewed.

• Spectral distribution of the $2S \to 1S$ two-photon transition in atoms and few-electron ions

The two-photon decay of the $2S$ state to the ground state in dressed atoms and oneor two-electron ions has been studied for several decades. Relativistic calculations have shown an 𝑍-dependence of the spectral shape of this two-photon transition in one- or two-electron ions. We have measured the spectral distribution of the $1s2s {}^1 S_0 \to 1_s {}^2 {}^1 S_0$ two-photon transition in He-like tin at the ESR storage ring using a new approach for such experiments. In this method, relativistic collisions of initially Li-like projectiles with a gaseous target were used to populate exclusively the ﬁrst excited state, $1_s2_s$, of He-like tin, which provided a clean two-photon spectrum. The measured two-photon spectral distribution was compared with fully relativistic calculations. The obtained results show very good agreement with the calculations for He-like tin

• X-ray microbeams based on Kumakhov polycapillary optics and its applications: Analytical consideration

Kumakhov polycapillary optics is based on the effective passage of X-ray radiation through bundles of monocapillaries of various conﬁgurations. The passage of radiation takes place because of the total external reﬂection of X-rays from the inner capillary walls. In this work,the basic characteristics of intense quasi-parallel X-ray polycapillary microbeams from a laboratory source with microfocus X-ray tube/polycapillary cylindrical structure are investigated theoretically (analytical consideration). The data generated from theoretical estimations are compared with the experimental results. Several new generations of X-ray analytical devices like, laboratory synchrotron, ﬂuorescent spectrometers, reﬂectometers/refractometers, diffractometers, X-ray microscopes and combinations of several such devices, are developed based on polycapillary optics. Besides, a number of devices can be developed for the most modern research problems such as nanomateriology, namely, X-ray nanoscanner, portable X-ray nanothickness indicator etc. X-ray tubes and the radiators, specially developed for polycapillary optics as efﬁciently as possible, are used in all the devices mentioned above.

• Energy-dispersive X-ray ﬂuorescence study of elemental uptake in cauliﬂower

A109Cd radioisotope-induced energy-dispersive X-ray ﬂuorescence (EDXRF) study has been performed on samples of cauliﬂower consisting of the flower, the leaves and the associated root soil. The cauliﬂowers were collected from farms near the main dumping site of municipal solid waste in the city of Kolkata, India and also from uncontaminated farms about 50 km away from the city. A uniﬁed calibration approach was undertaken for the elemental analysis of the samples of widely varying matrices. The present study suggests that the elemental concentrations in the root soils and leaves of the samples vary from farm to farm, whereby the concentrations of Cu, Zn and Pb in root soils of MSW-contaminated farms are higher by almost an order of magnitude compared to uncontaminated farms. But, the most notable feature of this study is the strikingly similar elemental concentrations in the edible ﬂower part of all samples irrespective of the type of soil.

• 6 MeV storage ring dedicated to hard X-ray imaging and far-infrared spectroscopy

The tabletop storage ring, 6 MeV MIRRORCLE, is dedicated to hard X-ray imaging as well as far-infrared (FIR) spectroscopy. In spite of low electron energy, the 6 MeV MIRRORCLE generates hard X-rays ranging from 10 keV up to its electron energy and milliwatt order submillimetre range FIR rays. Bremsstrahlung is the mechanism for the hard X-ray generation. Images produced with $11 \times$ geometrical magniﬁcation display a sharply enhanced edge effect when generated using a 25 mm rod electron target. Bright far-infrared is generated in the same way using a conventional synchrotron light source, but with MIRRORCLE the spectral ﬂux is found to be $\sim 1000$ times greater than that of a standard thermal source. Partially coherent enhancement is observed in the case of FIR output.

• Trace determination of uranium in fertilizer samples by total reﬂection X-ray ﬂuorescence

Uranium is reported to be present in phosphate fertilizers. The recovery of uranium from the fertilizers is important because it can be used as fuel in nuclear reactors and also because of environmental concerns. For both these activities suitable method of uranium determinations at trace levels in these fertilizers are required. Studies have been initiated for such TXRF determination of uranium and the results are reported in the present paper. For TXRF determinations the fertilizer samples were processed with nitric acid and the uranium present in it was removed by solvent extraction using tri-n-butyl phosphate as the extractant. The organic phase containing uranium was equilibrated with 1.5% suprapure nitric acid to bring out uranium in aqueous phase. This aqueous phase was mixed with internal standard Y and the TXRF spectra were measured by depositing samples on ﬂoat glass supports. The amounts of uranium in four fertilizer samples of Hungarian origin were determined by processing these TXRF spectra. Uranium concentrations in two fertilizer samples were found to be in the range of $4–6 \mu g/g$, whereas two fertilizer samples did not show the presence of uranium. The precision of the TXRF determination of uranium was found to be better than 8% ($1\sigma$).

• Application of total reﬂection X-ray ﬂuorescence spectrometry for trace elemental analysis of rainwater

Applicability of total reﬂection X-ray ﬂuorescence (TXRF) spectrometry for trace elemental analysis of rainwater samples was studied. The study was used to develop these samples as rainwater standards by the National University of Singapore (NUS). Our laboratory was one of the participants to use TXRF for this study. The rainwater sample obtained from NUS was analysed by TXRF and the trace elements Mn, Fe, Ni, Cu, Zn, V and Pb were determined as required by the NUS. The average precision was found to be within 16% and the TXRF-determined elemental concentrations of these elements were below $20 \mu g/l$. The average deviation of TXRFdetermined values from the certiﬁed values were 20% (excluding the deviation for Fe and V which were comparatively high). Apart from the above elements, S, K, Ca, Rb, Sr, Ba and Br were also determined by TXRF and were found to be in the range of 0.2 to 191 $\mu g/l$. TXRF-determined values of our laboratory played an important role in the certiﬁcation of concentration of seven elements in this rainwater sample which was later developed as a rainwater standard.

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