15)X-ray Spectrometry– HVC Capacitor, HV Ceramic Capacitor to build All kinds of X-ray machine.
Pettifer et al. (I7 ) showed that using third-generation synchro-
tron sources by allowing the collection of absorption spectra below
10
-6
relative statistical error, and energy-dispersive detection mode
with minimal energy drift, magnetostriction can be detected by
differential X-ray absorption. Rapid measurements of the difference
in EXAFS from the Fe K edge in an iron-cobalt thin film
undergoing periodic strain through magnetostriction were carried
out, using a magnet rotating around the sample. The magnitude
of the recorded signal relative to the noise showed a sensitivity
to mean differential atomic motion of 1 fm, 100 times more than
the presently stated accuracy of atomic distance determination
by EXAFS.
In recent years, the ability to interpret and analyze XAS data
has progressed dramatically, mainly due to the rapid development
of ab initio theories of the absorption spectrum. Advances of data
treatment techniques aiming at quantitative structural analysis
using XAS were also reported in the review period. Ravel ( I8 )
presented a practical introduction to the real-space multiple
scattering theory, used by the widely used FEFF program, and
its applications to the XANES and EXAFS regions of the spectrum.
The paper gives an excellent overview that is accessible to the
nonexpert synchrotron experimentalist conducting XAS. Di Cicco
and Trapananti (I9 ) developed a method for structural refinement,
based on the reverse Monte Carlo (RMC) algorithm. The method
is designed to study molecular and condensed systems incorporat-
ing all of the advances related to the application of modern multiple
scattering codes and the n-body expansion for XAS data analysis
(GNXAS). For the purpose of XAS refinement of liquids or
amorphous systems, the initial configuration can be successively
refined to reproduce the shape of the pair distribution function
g(r) obtained by diffraction experiments or by computer simula-
tions. Therefore, the starting configuration for XAS refinement of
liquid or amorphous systems can be a truly disordered structure
already compatible with previous experiments or calculations.
Simultaneous refinement of raw XAS and diffraction data is
possible by the method, giving realistic reconstructions of the local
structure compatible with the results of both techniques. The RMC
method was found to be superior to the peak-fitting XAS data
analysis approach based on model functions, especially for
disordered systems. XAS structural analysis of aqueous metal
complexes consisting of several components is a difficult task,
because the separation of the components is not possible.
Rossberg and Scheinost (I10 ) developed a new method for the
three-dimensional modeling of EXAFS spectra, which enables the
extraction of the local structure of aqueous metal complexes from
spectral mixtures of several components. The method is a
combination of MC simulations and target transformation factor
analysis (TFA). TFA is commonly used to test experimental
standard spectra if they are likely to be components in the set of
the unknown mixture spectra. In the reported new method,
theoretical EXAFS spectra of random arrangements between the
X-ray-absorbing metal ion and the ligand atoms are calculated
using MC simulation, to be tested by the TFA procedure as a
component. The coupled procedure is repeated until the error in
the test spectrum is minimized. The method can thus be used to
isolate and refine the structure of complexes from spectral
mixtures and to determine their relative concentrations, solely on
the basis of an estimate of a ligand structure. Micro-EXAFS spectra
of individual environmental particles are also spectral mixtures
of several components. Pinzani et al. (I11 ) reported a new
quantification procedure for the evaluation of the micro-EXAFS
data sets obtained from individual particles based on a RMC
approach, starting from a box with randomly placed atoms. The
standard RMC procedure was modified for Cd-L
3
edge micro-
EXAFS. Constraints on the distance of closest approach for each
pair of atoms, the local density function were treated with penalty
functions. As micro-EXAFS does not provide accurate information
on the chemical composition in the local environment of the Cd
atoms, simulations were executed with different chemical com-
positions. Applying the method for municipal waste incinerator
fly ash particles, cadmium was found to be present in both
crystalline and amorphous states within the microspots analyzed.