11)X-ray Spectrometry– HVC Capacitor, HV Ceramic Capacitor to build All kinds of X-ray machine.
Since the TXRF is a well-accepted technique for analysis o
ultrapure materials and very low level of contaminant trace-elemen
concentration, the accuracy of the final results is a central problem
In this field, the research group of Hellin ( F4) published on th
identification of the origin of the nonlinear effect of the micro
droplet residues. They observed, through their experiments,
systematic decrease of the accuracy of the determined elementar
content starting from 3 to 10 ng, depending on the sampl
composition. They set up a new mathematical model for consid
eration of the mass absorption calculation for microdroplet residu
samples, and the theoretical calculations were verified exper
mentally. The residue mass, after drying up the droplet spotting
was distributed mostly in a ring form and this shape must b
considered in any type of mathematical model calculations. Fo
the experimental testing, they used dilution of ICPMS calibratio
standards, droplets of 50 and 10 mL were deposited on
hydrophobic Si wafer, and the analysis were carried out for K
Ca, Cr, Fe, Ni, and Zn. To avoid the absorption by air for low-
elements between sample and detector, the intensive charac
teristic peak of the Ar and the scattering effects of air that in
crease the background in the detected spectra, Streli et al. (F5
developed a special chamber for TXRF analysis that can operat
under vacuum conditions (10
-2
mbar). The new design i
equipped with a 12-position sample changer, a 10-mm
2
SDD havin
an 8-ím Be window, and an electrical Peltier cooling system. Th
system can be attached to a diffraction X-ray tube (3-kW long fin
focus Mo tube) and a Mo/Si multilayer for monochromatizatio
of the primary X-ray beam. The detection limit for this TXRF
spectrometer was 700 fg for Mo-K R excitation using a 50-kV hig
voltage, a 40-mA tube current, and a 1000-s acquisition time; fo
a Cu anode tube under the same measuring conditions, it wa
52 pg.
A new spectroscopic method was reviewed by Tanida ( F6),
which is a combination of TXRF and XAFS investigations of the
structure and composition of liquid surfaces. The method is
suitable for the analysis of ions segregated on the solution surface
and monolayers of metal complexes at the solution surface in situ
by measurement of total electron yield and XRF. The surface
analysis requires extra stability and precision regulation of the
unwanted accidental movement of the sample holder; therefore,
the sample holder floats on an ethylene glycol/water pool and
permanent magnets provide the mechanical stability of the sample
holder tank. The experiments were carried out with monochro-
matized SR for Br and Zn K edge regions; those elements were
in different complex monolayer films on the water surface.
In a second paper, Streli et al. reviewed ( F7) the technical
details of their new compact vacuum chamber developed for TXRF
analysis (WOBISTRAX) as a low-Z atomic number (down to Na)
setup, illustrating the construction with many photos and figures
and with examples that show the analytical capabilities of this new
design. The applied SDD has a resolution of 140 eV at 5.9-keV
X-ray energy using a 0.5- ís shaping time and the 8-ím-thick Be
window. For the spectra evaluation procedure and the quantifica-
tion calculations, the AXIL and QXAS softwares were applied,
respectively.
Many papers published on TXRF analysis emphasize that the
method is very suitable for direct analysis of liquid samples
originating from the natural environment. Za ´ ray et al. ( F8)
published results on TXRF analysis of freshwater biofilms grown
on polycarbonate substrata in different lakes, for Ca, K, Fe, Mn,
Zn, and Sr. The authors estimated the enrichment factors for these
elements and found it to be in the range of 3 10
4
-1.5 10
2
.
The highest factor was found for micronutrients for Mn and Fe.
The authors investigated the identity and variation of the ac-
cumulated metal content in biofilms originating from different
geographical places and from different biochemical conditions,
and they found deviations from 20 to 80%, especially for Mn and
Fe. Those differences were not proportional to the elementary
concentrations in the water. These results confirm the assumption
that this behavior can be related to different algological composi-
tions and their metabolism.
A new construction of a TXRF spectrometer was reviewed by
Tiwari et al. ( F9). That machine provides angular resolution for
two different sample stages, and it has the possibility for precise
independent motions for vertical translation and angular rotation
for the sample and the use of a variety of primary beam
modification units, such as multilayers, crystal monochromators,
and curved mirrors. Different energies of X-ray tubes can be
applied for sample element excitation, and against this high
flexibility of the spectrometer, the construction is rather simple
and the analysis quite fast. Changing the measuring setup in the
spectrometer for a new configuration requires short time.
Grazing exit electron probe microanalysis on light elements
in aerosol particles was published on by Spolnik et al. ( F10 ). In
this measuring setup, the angle of the excitation electron beam
to the surface of the sample holder is 90 °, and the characteristic
X-rays emitted by the sample elements are detected in grazing
direction under an exit angle of less than 1 °. In this geometrical
arrangement, the X-ray intensity emitted by substrate disappears
under grazing exit angles. The authors analyzed artificial and
atmospheric particles for low- Z elements down to C using a
superthin polymer window for the Si(Li) detector. It was shown
that it is possible to observe the surface layer of the particles
without any influence of the X-rays emitted from the core of the
particle. BN and CaCO
3 artificial particles were suspended in
acetone, a few microliters were dropped onto the surface of a
sample holder (Si wafer), and the particles were covered by a C
layer of 0.2-nm thickness.
Chen and co-workers ( F11 ) developed a new design of doubly
curved crystal (DCC) for purposes of focusing X-rays in an TXRF
spectrometer when a low-power X-ray tube (Mo, Cu, Cr tubes) is
available for sample excitation. The DCC was built on Si (220)
for Mo-K R1, Si(111) for Cu-K R1, and Ge(111) for Cr-K R1 lines, and
all of them were constructed in such a way that the whole surface
of the crystals reflects the incoming X-ray beam into the same
identical geometrical point in a Rowland circle. This construction
allows decreasing the minimum detection limit into the range of
20 -150 fg, when measuring during 1000 s with 10 -50-W genera-
tor power. The average sensitivity was found to be 1.0 counts
s
-1
pg
-1
and the irradiated sample area was 100 ím
2
; that yielded
a much higher spatial resolution compared to conventional TXRF
spectrometers.
A report on combination of the TXRF technique and portable
spectrometers was published by OÄ va ´rietal.( F12 ) for the analysis
of natural freshwaters from the Tisza River catchments area in
Hungary, to disclose the influence of mining activities and the
possible heavy metal contamination levels. The greatest benefit
of the use of portable TXRF in field analysis is that a rapid
screening is possible for trace elements that should be the basis
for further decisions on the sampling strategy. They analyzed
natural biofilms that are sensitive monitors for metal contamination
in natural water and concluded on the basis of the results that
they can distinguish between suspended and dissolved element
fractions.
ELECTRON PROBE MICROANALYSIS
The recent increase of the speed of low-cost personal comput-
ers opened the possibility of wider utilization of Monte Carlo (MC)
simulations in quantitative EPMA. MC-based quantification meth-
ods can be advantageous in comparison with conventional ZAF
and æ(Fz) methods, mainly because they are not limited to
idealized geometries. However, the accuracy of MC calculations
strongly depends on the fundamental physical parameters, such
as the elastic-scattering cross sections and ionization cross
sections for electrons. Jablonski et al. (G1) addressed the
calculation of reliable differential cross sections (DCS) of elastic
scattering for describing electron transport in solids. A code
named ELSEPA (ELastic Scattering of Electrons and Positrons
by neutral Atoms and ions) has been developed that calculates
elastic DCSs for electrons and positrons using the relativistic
partial-wave expansion method. The scattering potential consid-
ered in ELSEPA includes the electrostatic potential, the local
exchange potential (only for the case of electron scattering), and
the correlation -polarization potential, as well as the absorption
potential. The authors compared calculated elastic DCSs for Si
and Au at selected energies relevant for EPMA (500 eV, 5 keV,
30 keV). A significant influence of the electron-exchange correc-
tion was observed at 500 eV. The correlation-polarization cor-
rection was found to be significant for small scattering angles at
500 eV, while the absorption correction was found to be essential
at energies below 10 keV. Another important physical parameter
is the ionization cross section, which was addressed through
measurements of the X-ray emission efficiency of K lines, for
selected elements in single-element samples as well as for
compounds and alloys, using a calibrated EDX detector with
known detection efficiency and solid angle, by Procop (G2).
Careful calibration of the spectrometer allowed the reduction of
the overall uncertainty in the measurement to 5-10%. The author
compared the measured X-ray emission efficiencies with calculated