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Imre Szalo´ki Ja´ nos Osa´n Rene´ E. Van Grieken*
OVERVIEW
In this review, we focus on the most significant and essential
progress in X-ray spectrometry (XRS), published in the period
2004-2005, covering the developments and improvements in the
performance of detection and instrumentation of X-ray techniques
and X-ray optics, new quantification models in X-ray spectra and
data evaluation, calculation and experimental determination of
fundamental atomic data, tomography and holography methods
for 2D or 3D imaging of microstructures, electron probe micro-
analysis (EPMA), total reflection X-ray fluorescence (TXRF),
particle-induced X-ray emission (PIXE) analysis, and X-ray absorp-
tion spectrometry (XAS). Finally, different applications in each
subfield of XRS are shown. This review involves only a selected
minority of the published papers and we try to look over the
current trends in this analytical field with a critically selected citing
of papers, to support the research activity of the community of
X-ray scientists.
Since our last review, an international group of scientists
published two overviews on XRS (A1, A2)inthe Journal of
Analytical Atomic Spectrometry, covering the period 2003 -2004
in the main field of this analytical spectroscopic method and
instruments. These review articles involve all the important
sections of XRS in nine chapters: reviews, instrumentation,
spectrum analysis, matrix correction and calibration, X-ray optics
and microfluorescence, synchrotron radiation, TXRF, portable and
mobile X-ray fluorescence (XRF), and on-line XRF and applications.
In the present review, we follow another way for classification of
the information published in the literature in the 2004-2005
period: detection, instrumentation (except of detectors) and
optics, quantification models and related fundamental data, to-
mography, and holography methods as the main tool of X-ray
imaging, TXRF, EPMA, PIXE, XAS, and a final chapter that
reviews the application of these methods in geology, environmen-
tal research, industry, biology. and medicine. Current trends in
pixel-type detectors were reviewed by Wermes (A3) showing their
necessity in X-ray imaging devices, radiography, autoradiography,
protein crystallography, and X-ray astrophysics research. The
fundamental aims of R&D activity in the field of detectors are to
arrange less material in the detector bulk, to build high-speed
readout electronics, and to construct large radiation-tolerant
detectors. The author describes the working principle and
structure of different categories of pixilated detectors: hybrid pixel
detectors when the sensor module and the electronic chips are
connected by short bumps, diamond detectors and their applica-
tions for protein crystallography and radiography. The author
describes the dream of the detector developer: a fully monolithic
pixilated detector where both the sensor bulk and the electronic
circuits are in one entity and these devices can be produced by
commercially available technology, and he outlines that this will
not be possible in the future due to the lack of proper technology.
In the past decade, the greatest hit in XRS was probably the
cryogenically cooled quantum detectors such as superconductive
tunnel junction (STJ), transition edge sensors (TESs), and micro-
calorimeters. These provide excellent energy resolution for a wide
range of X-ray energies, from the optical range up to several
kiloelectronvolts. Kurakado published (A4) a short characteriza-
tion about nonequilibrium superconductivity and STJ detectors.
The tutorial paper introduces the reader into the main features,
such as high count rate capability, stability against temperature
fluctuation, ultra-high-energy resolution, and the working principle
of the STJs. The most common Nb/Al/AlOx/Al/Nb structure has
excellent working parameters and very high stability against
temperature variation from 50 to 500 mK. A 100 100 ím
2
Al
STJ located on a Si
3N4
membrane, covered by a 1.3-ím-thick Pb
absorber, was described; this device had an energy resolution of
12.4 eV and the noise was 4 eV at 5.9-keV X-ray energy. Lankosz
et al. ( A5) reviewed quantitative X-ray microanalysis for biological
and glass material samples in order to verify the fundamental
parameter method on the basis of the application of standard
samples. The principal aim of their investigation was to determine
the analytical capability of a microbeam (X-ray beam diameter of
30ím) XRF spectrometer equipped with capillary optics. They
considered all the possible sources of uncertainty of the whole
analysis: operating stability of the detector and X-ray source,
sample movement, and errors originating from the spectral
deconvolution calculations. The sample thickness was estimated
on the basis of the measurement of the elastic and inelastic
scattered intensities of the source radiation, and it was applied
for the matrix correction as well. The authors demonstrate their
analytical considerations and calculations by some examples using
the synchrotron microbeam XRF technique for quantitative
analysis of human brain tissue samples with both monoenergetic
and polychromatic excitation modes. The accuracy for glass
standard samples was found between 4 and 40% relative.
Janulewicz et al. ( A6) reviewed the state-of-the-art of the tabletop
type X-ray lasers (XRLs) and described the working principle of
these lasers and their characteristic spectral output properties,
from a practical point of view. They concluded that the XRL
sources are competitive in comparison with the third-generation
synchrotron radiation (SR) facilities: brilliance of the beam and
time-resolved measurements. The author details the operating
processes of two types of XRFs based on the quantum pumping
mechanisms in generating the excitation states: (i) recombination
and (ii) collisional-type XRLs. The size of the XRLs is the central
problem in development research; it can be decreased in the case
of a hybrid-type XRL, when the pumping medium is gas plasma
in a capillary tube in which the inverse population is generated
by a short picosecond optical laser beam, entering into the axial
direction of the capillary. Most observed objects in the sky
naturally emit X-ray radiation that transports information on the
atomic-level processes occurring in the source objects, on the
motion of the bulk material, etc., or the transmission of X-rays
through absorption can be studied. Therefore, the detectors of
X-ray telescopes are the central devices in the sky observatories,
such as Chandra and XMM-Newton. Porter reviewed ( A7) the
low-temperature detectors developed for space missions such as
X-ray cameras and dispersive X-ray spectrometers. The Astro-E2
launched in 2005 was the first mission that contained a low-
temperature microcalorimeter-based observatory, and three more
low-temperature detector-based observatories are being developed
(NeXT, Constellation-X, ZEUS). Due to the high-level ionization
of the individual atoms in different sky objects, very complex X-ray
emission spectra must be detected resolving the satellite lines.
The newest spectrometers that suit this requirement are high-
energy resolution microcalorimeters. The other essential group
of X-ray detectors are the CCD cameras; these have moderate
spectral sensitivity and therefore they have to be used with
selective absorbing filters for energy-sensitive X-ray imaging. In
the future observatories, new detector types are needed, which
have1000 pixels with a high-energy resolution below 4 eV at
6-keV X-ray energy, in a miniature, monolithic arraying form,
