JRA2 XRD portable (18 months) - Eu-ARTECH

SECOND ANNUAL REPORT - DELIVERABLE N. 34
JRA2-Task 3- Progress report on optimal conditions
for XRD studies
(18 months)
Eu-ARTECH
Access, Research and Technology for the conservation of
the European Cultural Heritage
Integrating Activity
implemented as
Integrated Infrastructure Initiative
Contract number: RII3-CT-2004-506171
Project Co-ordinator: Prof. Brunetto Giovanni Brunetti
Reporting period: from June 1 st 2005 to May 31 st 2006
Project funded by the European Community
under the “Structuring the European Research Area”
Specific ProgrammeResearch Infrastructures action

JRA2 Task 3 - Report on optimal conditions for artwork XRD studies and XRD and XRF
assembling
Resp. C2RMF – A.Gianoncelli, J.Castaing
Introduction
The complete knowledge of materials characteristics requires the determination of the different phases
(chemical composition, crystal structure) that are present in an object and the description of the
microstructure (grain size, texture, lattice imperfections, etc.). The target of the project is to obtain this
information thanks to a new tool for in situ studies of the constitutive materials of artworks by means of X
ray fluorescence (XRF) and X ray diffraction (XRD). In the first twelve months, an assessment of the
possible geometries has been made and general specifications have been established. We ruled out the
energy dispersive X ray diffraction (ED-XRD) option based on a literature survey. However, we performed
diffraction experiments to compare the performance of ED-XRD with traditional angular detection; we
present the first results that confirm our initial choice.
Another choice has been made concerning the detection of diffracted beams; we purchased an imaging plate
system and have started to test it for XRD recording.
Energy dispersive X-ray diffraction experiments
Energy Dispersive X-ray diffraction (ED-XRD) experiments have been carried out at the Laboratoire de
Cristallographie (CNRS UPR 5031) in Grenoble in order to test the performance of this method for a
portable XRD instrument.
X-ray diffraction occurs when there is constructive interference between incident and diffracted waves; this
means that the path difference between the two waves must be an integer number of wavelengths.
This leads to the Bragg’s law:
2 d sin ϑ = nλ
= n (1.24 / E)
where d is the spacing between the planes in the atomic lattice
is the wavelength of the incoming x-ray of energy E (in keV for in nm)
n is an integer
¡ is the angle between the incident beam and the scattering planes.
Angle dispersive methods rely on the identification of the angles ¡ corresponding to constructive
interference, once has been fixed.
Energy dispersive methods allow to recognise the crystal structure of the sample (d-spacing) by analysing the
energy of the peaks present in the spectra, acquired at a fixed angle ¡ .
The following instrumentation was used during the test:
- Cu anode X-ray tube biased at 40 kV and 40 mA;
- Si(Li) detector, 8 ¢ s peaking time, nominal energy resolution of 180 eV @ Mn K£ line (5.898 eV).
- Goniometre to rotate detector and sample independently
A few different specimens have been analysed: polycrystalline silicon, quartz, calcite and calcite covered by
a thin layer of goethite.
The measurement have been taken at two or three different 2¡ angles for each sample; this results in a shift
of the peak position (energy) by changing the angle.
We show the results obtained for polycrystalline silicon (figures 1 and 2). The position of the peaks for
Polycristalline Si is indicated in table 1, according to the crystalline plane and to the angle between X-ray
beam and detector axis (2¡ ).
Due to difficulties in the alignment of the system, the geometry of the experiment is not well known, in fact
the detected peaks correspond to the angles indicated 2θ=31° and 2θ=36°.

hkl
d-spacing
[Å]
Table 1.
position [keV]
@ 31°
position [keV]
@ 36°
111 3.1355 7,398 6,398
220 1.9201 12,081 10,448
311 1.6374 14,167 12,252
400 1.3567 17,098 14,787
331 1.2459 18,619 16,102
422 1.1085 20,927 18,097
This kind of sample is an ideal one because its fluorescence peaks are in the low energy range (Si K£ is at
1.740 keV); in this way the diffraction peaks can only interfer with the Cu peaks due to the anode of the Xray
tube. The Si peaks are not visible in the spectrum because of the absorption of the air (the distance
between sample and detector is around 15 cm).
For most complicate or multi-elemental samples, the overlapping of fluorescence and diffraction peaks can
make the peak identification more difficult.
Figures 1 and 2 show the spectra acquired at two different angles. Peaks have been identified as diffraction
peaks: the corresponding crystalline plane is indicated in the spectra.
- Figure 1. Spectrum of a polycristalline Si, acquired with the Si(Li) detector and 2¡ 1=30°;
measurement time (real time): 150 sec

- Figure 2. Spectrum of a polycristalline Si, acquired with the Si(Li) detector and 2¡ 1=35°;
measurement time (real time): 150 sec
As expected, by changing the 2¡ angle, the diffraction peak energy changes. For instance, the (111) peak is
included in the fluorescence Cu-Kα in figure 1 and it is visible in figure 2, but it coincides with the escape
peak.
Similar observations were made on the other compounds. In these cases, the fluoresecnce of Ca and Fe from
the specimens add up to the fluorescence of copper that originates from the X ray source.
Although the measurements showed that it is possible to identify the diffraction peaks by using energy
dispersive methods, this technique does not seem suitable for mineral identification with a portable
instrument. The diffraction peak intensity is quite weak and the peak width is quite large, due to the detector
energy resolution and to the superposition of different diffraction peaks.
Fluorescence peaks can strongly interfere with diffraction peaks making their identification more difficult.
Moreover fluorescence peaks are usually much more intense than diffraction ones.
In principle these problems could be overcome by systematically doing measurements at several different
angles. This could be done in a relatively quick measurement time by using a multi-element detector or some
single detectors located at different 2θ angles. This solution would allow to evaluate the geometry and to
separate diffraction and fluorescence peaks. On the other hand this requires a complex and heavy equipment,
and also a non-trivial data analysis.
This supports our initial conclusion, based on the literature, to rule out the ED-XRD for the planned portable
system.
X-ray Diffraction experiments with Imaging Plate
The experiments have been performed at the Laboratoire de Cristallographie (CNRS UPR 5031) in
Grenoble. The source used is a Philips C-Tech type x-ray tube, with Cu anode and a maximum power of
2200 W (60 kV). The x-ray beam is monochromatic by means of two mirrors: only Kα1, Kα2 and Kβ appear
in the spectrum (with approximately the following ratio between intensities Kα/Kβ≈10 -3 ÷10 -4 ).
The divergence of the beam is approximately 0.05° and its dimension is around 1.5mm x 1mm in the centre
of the goniometer, with a flux of around 10 7 ph/s.
The tube is biased at 50 kV and 40 mA.
Different kinds of samples and different times of measurement have been taken into account in order to test
the system.
For each sample two XRD detector systems have been used:
- a conventional scintillator detector, with a monochromator in front of it, in a θ-2θ configuration

- an Imaging Plate (IP) perpendicular to the incident X-ray beam at distance of around 20 cm from
sample, with ω being the angle between x-ray beam and sample surface.
Here, we present the results obtained for quartz. For a measurement time less than 5 min the IP scanner did
not read anything.
Since the first image with the fixed sample showed some preferential orientation (punctuation on the rings)
of the crystals in the quartz, further measurements were taken with the sample turning on itself in order to
obtain a more uniform diagram (figure 3).
Figure 4 and 5 show a comparison between the diagram recorded by the scintillator detector (1h and 6
minute measurement) and the diagram obtained from the fitting (Fit2D) of the image recorded with the
Image Plate (10 minutes), respectively. Considering the measurement times and the intensity shown in the
diagram, the efficiency of the imaging plate appears quite high.
Figure 3. Diagram recorded on the imaging place for a turning quartz sample irradiated for 10 min with a
monochromatic radiation (Cu K£ ) and ω=15°, read at 16 bit.
Figure 4. θ-2θ XRD diagram for quartz, recorded with a scintillator detector over a 2θ range from 20° to 60°
(0,05°/step with 5s/point) for a total measurement time of around 1h and 6 minutes.

Figure 5. Result of the fitting of an XRD diagram recorded with an imaging plate, for a quartz sample
irradiated for 10 min and =15° (16 reading bits).
The imaging plate detector proved to be a valid alternative to the one-dimensional scintillator detector: the
measurement times are comparable (around 20÷30 minutes for both), even if imaging plate seems to be more
efficient. Imaging plates have the big advantage of being a two-dimensional low-noise system, with a
flexible mounting and wireless, and they allow to collect data in a parallel detection configuration. On the
other hand the scanner system requires around 3 minutes to read the recorded image (it is not an online
measurement; the result is visible only at the end of the process) and imaging plates are light sensitive.
Further tests are in progress in order to determine the needs for an analyzer for the diffracted beams and the
types of slits/diaphragms necessary for optimal XRD. This is will allow to choose the optimal X ray source
compatible for XRF and XRD.