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836 http://dx.doi.org/10.1107/S1600577516004483 J. Synchrotron Rad. (2016). 23, 836–841
Received 8 December 2015
Accepted 15 March 2016
Edited by J. F. van der Veen
Keywords: X-ray emission spectrometer; Johann
geometry; XANES; HERFD; XES; RIXS; actinides.
A Johann-type X-ray emission spectrometer
at the Rossendorf beamline
Kristina O. Kvashnina
a,b
* and Andreas C. Scheinost
a,b
a
Rossendorf Beamline at ESRF – The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France, and
b
Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, PO Box 510119, 01314 Dresden,
Germany. *Correspondence e-mail: kristina.kvashnina@esrf.fr
This paper gives a detailed description, including equations, of the Johann-type
X-ray emission spectrometer which has been recently installed and tested at the
Rossendorf beamline (ROBL) of the European Synchrotron Radiation Facility.
The spectrometer consists of a single spherically bent crystal analyzer and an
avalanche photodiode detector positioned on the vertical Rowland cycle of 1 m
diameter. The hard X-ray emission spectrometer (3.5–25 keV) operates at
atmospheric pressure and covers the Bragg angles of 65–89. The instrument
has been tested at high and intermediate incident energies, i.e. at the Zr K-edge
and at the Au L
3
-edge, in the second experimental hutch of ROBL. The
spectrometer is dedicated for studying actinides in materials and environmental
samples by high-energy-resolution X-ray absorption and X-ray emission
spectroscopies.
1. Introduction
The community of synchrotron radiation users at hard X-ray
absorption beamlines frequently requests access to X-ray
emission spectrometers. There are several reasons for this
current demand, which is expected to further increase in the
future. First, compared with conventional methods, high-
energy-resolution fluorescence detection (HERFD) (de Groot
& Kotani, 2008) using an X-ray emission spectrometer allows
X-ray absorption spectra to be recorded with substantially
better energy resolution (Ha
¨ma
¨la
¨inen et al., 1991), since the
spectral broadening of the absorption features is drastically
reduced in the case of the HERFD method (de Groot et al.,
2002). At the same time, the background, generated by other
elements in the investigated materials, is minimized by the
use of the crystal analyzer in the X-ray emission setup. Thus,
the lower detection limit of elements can be considerably
decreased, even in complex materials down to the lower p.p.m.
level, and/or the counting time can be reduced (Kvashnina et
al., 2009). Finally, in the case of elements with little energy
distance between their absorption edges (e.g. for neighboring
lanthanides), the interference of these absorption edges can
be eliminated in certain cases by a specific crystal analyzer
(Hu
¨bner et al., 2011).
Second, X-ray emission spectroscopy provides the possibi-
lity to record the valence and core X-ray emission lines with
resonant and non-resonant excitations (Glatzel & Bergmann,
2005; Vanko
´et al., 2006; Kvashnina et al., 2014). This becomes
very important when investigating the ligand orbitals of
a selected element and the crystal structure of materials
(Safonov et al., 2006; Smolentsev et al., 2009). There are also
other techniques which could be developed, when X-ray
ISSN 1600-5775
#2016 International Union of Crystallography
emission spectrometers are more freely available, such as non-
resonant (Raman) X-ray scattering (Krisch & Sette, 2002).
This method allows the soft X-ray transitions to be probed by
the incident hard X-rays. Unfortunately, the cross section of
this process is very low and requires technical improvements
for emitted energy paths (e.g. a multiple crystal analyzer
setup).
Technically, an X-ray emission spectrometer consists of a
crystal analyzer and a detector, which can be realized with
different geometries. The most renowned types are the
Johannson (Johansson, 1933), Johann (Johann, 1931) and von
Hamos (von Hamos, 1932) geometries. The existence of
various geometries provides the opportunity to build the most
appropriate instrument for the particular experimental
station. In the case of Johann and Johannson geometries, a
point-to-point focusing scheme is realized, where both the
crystal analyzer and the detector are moved when the emitted
energy is scanned (Bergmann & Cramer, 1998; Huotari et al.,
2006; Hazemann et al., 2009; Kleymenov et al., 2011; Kavc
ˇic
ˇet
al., 2012; Sokaras et al., 2013). This scheme provides a higher
detection signal, and covers a larger solid angle. In contrast,
the possibility of recording the emission lines with the energy-
dispersive (von Hamos) geometry is very practical since it
does not include movable parts (Szlachetko et al., 2012). Here,
we show the implementation of a very simple Johann-type
X-ray emission spectrometer with a single spherically bent
crystal analyzer and provide the equations for the calculation
of the positions of the crystal analyzer and the detector in the
X-ray emission setup. This setup was tested at the Rossendorf
beamline for actinide research. Installation of a multiple
crystal analyzer instrument with different Rowland cycle
diameters is foreseen in 2017.
2. Technical details
A single-crystal X-ray emission spectrometer with vertical
scattering geometry was mounted in the second experimental
hutch of the Rossendorf beamline (Matz et al., 1999) and
tested at intermediate (11 keV) and high (18 keV) ener-
gies. The incident energy was selected using the (111) reflec-
tion from a double Si crystal monochromator. For the Zr K-
edge measurements, the beam was both vertically and hori-
zontally focused with the Rh-coated toroidal section of the
mirror after the monochromator, while for the Au L
3
-edge
measurements we used the sagittally flat Si surface of this
mirror, i.e. obtaining only vertical focusing. In both cases, the
mirror was set at an incident angle of 2.5 mrad. The incident
monochromatic X-ray beam has a flux of 10
11
photons s
1
on the sample position at an energy of 12 keV, with a beam
size of 150 mm400 mm(VH). All samples were measured
simultaneously in HERFD mode by reflecting the detected
beam with the single-crystal analyzer, and directly in total
fluorescence yield (TFY) mode using a Canberra photodiode.
Incident energy was scanned by the monochromotor and two
signals for XANES measurements were collected at the same
time in HERFD and TFY modes.
The X-ray emission spectrometer consists of the crystal
analyzer and the detector, which are located together with the
sample on the Rowland cycle. The HERFD measurement is
then performed by scanning the incident energy across the
absorption edge of the selected element at the maximum of
the X-ray emission line. X-ray emission spectra are measured
by scanning the emitted energy with the crystal analyzer, while
keeping the incident energy fixed. If the incident energy is
selected above the X-ray absorption edge, non-resonant X-ray
emission spectra are recorded. If the incident energy is
selected below or near the absorption edge, resonant X-ray
emission spectra or resonant inelastic X-ray scattering is
recorded.
The basic principle of the spectrometers is that the energy
of the emitted fluorescence is selected by the Bragg reflection
of the crystal analyzer. According to Bragg’s law,
2dsin ¼n; ð1Þ
where is the scattering angle, dis the lattice spacing for the
given crystal orientation, nis the order of reflection, and is
the wavelength of the X-ray photons. For a crystal with cubic
symmetry, the d-spacing for a given crystal orientation can be
obtained through the following equation:
d¼a
h2þk2þl2
ðÞ
1=2;ð2Þ
where ais the lattice spacing and h, k, l are the Miller indices
of the Bragg plane.
The tabulated lattice parameters for common crystals are:
a¼5:6574 A
˚for germanium ðGeÞ;
a¼5:4309 A
˚for silicon ðSiÞ:ð3Þ
In this case, the Bragg angle for any energy (Ein keV) is
calculated using the following equation:
¼arcsin 6:19926 n
dE :ð4Þ
A schematic drawing of a typical Rowland circle setup is
shown in Fig. 1. The centers of sample, bent crystal analyzer
and detector are all located on a Rowland cycle with radius R.
The bent crystal analyzer with a fixed radius of 2Rreflects the
fluorescence X-rays from the sample to the detector. The
detector has to be shifted along the Rowland cycle, once the
Bragg angle or the emitted energy is changed. At the same
time, the angle of the bent crystal analyzer has to be changed.
To enable these movements of the crystal analyzer and the
detector along a vertical Rowland circle, we have established a
mechanical setup as shown in Fig. 2. During a measurement,
the sample rests always at the same place. The distance SC
between the sample and the center of the crystal analyzer is
kept equal to the distance CD between the center of the
crystal analyzer and the center of the detector,
SC ¼CD ¼2Rsin :ð5Þ
In order to keep the focusing geometry, the detector has to be
maintained at an angle (), which is twice the angle of the
crystal analyzer (),
beamlines
J. Synchrotron Rad. (2016). 23, 836–841 Kvashnina and Scheinost Johann-type X-ray emission spectrometer 837
¼2:ð6Þ
The detector, an avalanche photodiode (APD) of 200 mm
thickness, has been mounted on a goniometer, which in turn is
mounted on two linear stages marked DX and DZ in Fig. 2
arranged perpendicularly. The distances DX and DZ are
calculated according to the following formulas:
DZ ¼2SC sin 90 ðÞ
180 cos 90 ðÞ
180 ð7Þ
and
DX ¼2SC sin290 ðÞ
180 :ð8Þ
Like the detector, the crystal analyzer is also mounted on a
goniometer and two linear stages in perpendicular geometry.
The goniometer is used to position the crystal at the angle .
The AX linear stage moves the crystal analyzer in the SC
direction (Fig. 1), and the AY stage is mounted perpendicular
to AX. The second linear stage (AY) can be replaced by the
goniometer and has to be used to guide the reflected X-rays
from the crystal analyzer to the middle of the detector in the
horizontal plane.
During the first experiment, the Zr K-andAuL
3
-edges
have been measured at the maximum of the most intense K
1
and L
1
emission lines, respectively. Two types of spherically
bent crystal analyzers have been used: Ge (220) for the Zr K
1
line, and Ge (111) for the Au L
1
line, each with a bending
radius of 1 m. The calculated positions of all motors for both
emission lines are summarized in Table 1.
For the pre-alignment of all components, and to test their
proper coordinated movement along the Rowland circle, and
their orientation towards the detector, we used the following
laser setup. The laser itself was mounted perpendicular to
the direction of the X-ray beam and behind the sample stage
(Fig. 1). A non-transparent tape was mounted on the sample
stage in order to scatter the laser beam. First, the scattering
angle ()of90
was precisely determined using the laser
reflection by placing the crystal analyzer at 90and adjusting
the angle of the goniometer. The scattering from the tape
should match the position of the laser reflection at =90
.
Second, the position of the crystal analyzer at the correct
radius of the Rowland circle was adjusted using the laser.
When the crystal is placed at = 90.2, the reflected light from
the crystal is seen a few millimeters below the sample position
(or the laser reflection of the tape). The motion of the crystal
in the SC direction (AX motor) adjusts then the radius of the
crystal analyzer. Third, the detector was placed in the focus of
the crystal analyzer by using the laser light scattering as well.
The crystal analyzer was moved to the estimated Bragg angle
(79.22for the Zr K
1,
and 77.69for Au L
1
measure-
ments). By moving the DX and DZ motors, the detector was
then centered in the laser beam.
After this laser pre-alignement, the alignment was refined
with the X-ray beam by using the emitted fluorescence of the
test samples. We performed three scans: a scan in the range
0.2, an AY scan in the range 5 mm, and then another
scan with a finer step size using the Zr (and Au) foils. The
beamlines
838 Kvashnina and Scheinost Johann-type X-ray emission spectrometer J. Synchrotron Rad. (2016). 23, 836–841
Figure 2
Photograph of the X-ray emission spectrometer setup at the Rossendorf
beamline. The positions of the sample (S), crystal (C) and the detector
(D) are marked by the respective letters in pink. The linear stages of the
crystal analyzer and the detector are shown in yellow and marked as
AX, AY and DX, DY
Table 1
Calculated positions of the motors in the X-ray emission setup for the
maximum of the Zr K
1
and the Au L
1
emission lines.
Emission line
Zr L
1
Au L
1
Tabulated value 15.775 keV 9.713 keV
Crystal analyzer Ge 220 Ge 111
Reflection (n)5 5
Bragg angle 79.2277.69
AX 982.355 mm 977.013 mm
Detector angle 158.44155.38
DZ 360.963 mm 406.983 mm
DX 68.721 mm 88.802 mm
Figure 1
Schematic drawing of the Johann-type X-ray emission spectrometer.
emission energy was scanned by moving simultaneously the
AY, ,, DX and DZ motors. Finally, the sample was scanned
in the direction of the incident energy in order to place the
sample in the focus of the crystal analyzer. A scan of the
emission energy near the maximum of the Zr K
1
line at an
incident energy of 18.2 keV is shown in Fig. 3(a). The broad-
ening of the emission line, determined as half width at half-
maximum, is 5.5 eV.
3. Examples
The Zr K-edge XANES spectra of a Zr foil and of ZrSiO
4
powder are shown in Fig. 3(b). Both samples were measured
simultaneously in TFY and in HERFD modes at the maximum
of the Zr K
1
emission line. We did not find any difference in
the value of the maximum of the Zr K
1
emission line between
different samples. Therefore, the X-ray emission spectrometer
was not moved during the HERFD data collection on both
samples. The main features in the Zr K-edge XANES corre-
spond to the dipole-allowed transitions from the 1sto the 5p
states. The improved resolution of the HERFD spectra allows
identification of the clearly separated pre-edge structure in the
spectra of both Zr compounds, which arises from the dipole-
forbidden but quadrupole-allowed transitions between 1sand
4dstates. The pre-edge features indicate the distortion of the
crystal structure of the solids and show the effect of the
hybridization between the d,pstates of Zr and the unoccupied
states of the ligands. The HERFD spectra collected at the
Rossendorf beamline are in good agreement with the HERFD
spectra previously recorded by Wilke and co-authors at the
dedicated XES beamline of the European Synchrotron
Radiation Facility (ESRF), ID26 (Wilke et al., 2012). The only
difference is that Wilke and co-authors used a pair of Si (311)
crystals in the monochromator, which have a better incident
energy resolution.
Fig. 4 shows the Au L
3
-edge XANES spectrum of the Au
foil recorded in TFY and HERFD mode simultaneously. The
achieved energy resolution of the HERFD spectrum matches
previously reported results also collected at ID26 (Erenburg et
al., 2013). The intensity of the recorded HERFD and X-ray
emission spectrum was significantly lower compared with the
measurements at higher incident energy (Zr K-edge) due to
the considerable absorption of X-rays by air. We plan to
reduce the air paths in the space between the sample, analyzer
and the detector in the near future.
The energy resolution of the spectra can be further
improved by placing a slit in front of the detector. The count
rate can be further increased by installation of a crystal
analyzer with a bending radius of 0.5 m (the signal is expected
to be four times higher than in case of the crystal with a 1 m
bending radius). These options will be realized together with a
multiple-crystal X-ray emission setup at the Rossendorf
beamline at the end of 2017.
The count rate for the emitted energies above 11 keV can
be further improved by using a CdZnTe or other detector with
higher sensitivity for higher X-ray energies. There is another
possibility of increasing the signal-to-noise ratio, by moving
the crystal analyzer inside the Rowland cycle (Kavc
ˇic
ˇet al.,
2012). The total energy resolution will decrease, but the
sharpening effect of the HERFD data remains strong. Espe-
cially in cases where wide emission lines are used for HERFD
beamlines
J. Synchrotron Rad. (2016). 23, 836–841 Kvashnina and Scheinost Johann-type X-ray emission spectrometer 839
Figure 3
(a)ZrK
1
X-ray emission spectrum recorded on the Zr foil. (b)ZrK-
edge XANES spectra of the Zr foil and of ZrSiO
4
powder recorded in
HERFD (red) and TFY (blue) modes simultaneously.
Figure 4
Au L
3
-edge XANES spectra of the Au foil recorded in HERFD (red) and
TFY (blue) modes simultaneously.
data collection, the loss of the energy resolution has little
influence on the energy resolution of the HERFD spectra,
while improving the count rate drastically
4. Conclusions
This manuscript gives an overview of an X-ray emission setup
which can be constructed at any X-ray absorption beamline in
a relatively short time. It includes the single-crystal analyzer,
the detector, four linear stages and two goniometers. The
signal-to-noise ratio can be improved by installing several
crystal analyzers in a row, as realized for instance at the ESRF
beamlines ID26 (Glatzel et al., 2013), ID20 (Huotari et al.,
2006) and FAME (Hazemann et al., 2009), at the SLS beam-
line SuperXAS (Kleymenov et al., 2011), the ANKA beamline
INE and the SSRL beamline 6-2 (Sokaras et al., 2013).
Such X-ray emission spectrometers can be used as compli-
mentary instruments on any beamline. The possibility of using
the X-ray emission setup not only in a monochromatic but also
in a pink beam has been already demonstrated (Rueff et al.,
1999). The spectrometer is very compact and can be placed at
any position near the sample. Vertical or horizontal Rowland
geometries might be chosen depending on the beamline
requirements and restrictions. The electronic structure infor-
mation is very important and related to all types of experi-
ments, such as diffraction, scattering, imaging, etc.The
possibility of studying the investigated systems by different
techniques simultaneously is therefore heavily requested by
the user communities at many synchrotron radiation sources.
5. Future plans
We show here the first data measured at the Rossendorf
beamline by a single-crystal Johann-type X-ray emission
spectrometer. The spectrometer will be further developed for
studying nuclear waste materials and
environmental applications (Vitova et
al., 2010; Kvashnina et al., 2013, 2014;
Kvashnina & de Groot, 2014). The
current bulk X-ray absorption fine-
structure station of the ROBL is
equipped as an alpha-lab and allows
actinides and other radionuclides up to
185 MBq (Fig. 5) to be studied. Due to
the spatial restrictions of the current
alpha-glovebox, the X-ray emission
spectrometer could only be installed in
a second hutch, which does not provide
inherent protection from alpha-emitting
radionuclides. Therefore, only samples
in line with the standard ESRF safety
regulations for experiments with radio-
active samples can be currently
measured. The maximum activity per
sample under these conditions can be
found at the ESRF website. These are
for instance 640 kBq for Np-237,
300 kBq for Pu-238, and 340 kBq for Am-241 in the solid state.
The maximum total activity of all the samples is restricted to
3.7 MBq. To overcome this restriction, the second experi-
mental ROBL hutch containing the X-ray emission spectro-
meter will also be converted into an alpha-lab in 2018–2019
(Fig. 6). Both experimental hutches will be connected by a
lock room, which allows an easy transfer of radionuclide
samples between them, and therefore an easy access to the full
array of experimental techniques available at the beamline.
The maximum activity given in Fig. 5 will then be valid for all
samples and all techniques.
We plan to study nuclear materials as liquids and solids with
the help of the X-ray emission spectrometer. A special cell will
be designed in order to handle radioactive liquid materials. A
special cell will be provided for the in situ studies of nuclear
materials at low temperatures down to 10 K, with laser exci-
tations (pump and probe experiments) and at room
temperature. In certain cases, we will be able to perform high-
pressure experiments on single-crystal materials containing
actinides. Due to the safety regulations of ESRF, high-
temperature experiments on nuclear materials are forbidden.
All electronic transitions in the energy range between 5 and
35 keV can be studied in the high-energy-resolution mode at
the ROBL beamline. This includes the actinide and lanthanide
beamlines
840 Kvashnina and Scheinost Johann-type X-ray emission spectrometer J. Synchrotron Rad. (2016). 23, 836–841
Figure 5
List of radionculides and amount in mg to stay below the maximum
activity limit of 185 MBq permitted on ROBL.
Figure 6
The two experimental hutches of ROBL (marked in red) will be equipped as alpha-labs and
connected by a lock room (green). This will allow for an easy transfer of radionuclide samples
between both stations to investigate them with the full array of experimental methods available,
including the new spectrometer.
L-edges and transition metal K-edge absorption transitions.
The main effort will be on studies of the core level transitions
by means of the valence band XES and RIXS techniques,
thanks to the high incident X-ray flux, which will be available
for users after the ESRF EBS upgrade programme in 2018.
Acknowledgements
The authors would like to acknowledge the support of the staff
at the Rossendorf beamline. ID26 beamline at ESRF is greatly
acknowledged for providing four linear stages, two gonio-
meters and two crystal analyzers. The technical support of
Florian Ledrappier, Cedric Cohen, Elia Chinchio and Herve
Gonzalez is much appreciated. KOK would like to acknowl-
edge Simo Huotari for a fruitful discussion about spectro-
meter designs and invaluable help during the test of the X-ray
emission spectrometer.
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349–350, 15–25.
beamlines
J. Synchrotron Rad. (2016). 23, 836–841 Kvashnina and Scheinost Johann-type X-ray emission spectrometer 841
