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FIRST ANNUAL REPORT – DELIVERABLE N. 17
Report on
JRA2 : new methods in diagnostics: imaging and
Spectroscopy
Task 3 : Development of a non-destructive method for
in-situ diagnosis by XRD and XRF
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 1st 2004 to May 31st 2005
Project funded by the European Community
under the “Structuring the European Research Area”
Specific Programme Research Infrastructures action
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Introduction
The complete identification of materials requires the determination of the various phases that are
present as well as the examination of the microstructure (grain size, texture, lattice imperfections, etc.).
Combining X ray fluorescence (XRF) and X ray diffraction (XRD) is the most direct method to
achieve such identification although it is restricted to crystals, excluding amorphous phases, and it
does not provide detailed information on the microstructure.
The main target of the JRA2 task 3 is to perform material identifications with a new tool for in situ
studies of artworks by means of XRF and XRD. The main challenge is to define the conditions for
XRD measurements foreseeing the constraints of heritage objects: presence of surface layers; grain
sizes (from 1 µm to 5 mm) involving conditions from powder diffraction to single crystal diffraction.
This implies the study of a specific design of the mechanical parts holding X ray sources and detectors
in relation to the specimen under investigation.
General considerations about XRD and XRF
X ray diffraction (XRD): sub-task 3.1
When a beam of X rays is sent on materials, reflections occur when the beam hits crystalline matter
under the Bragg’s conditions:
 = 2 d sin
(1)
Here, “” denotes the wavelength of the X rays, “d” the spacing between the reflecting lattice planes
and “” the angle between these planes and the X ray beam (figure 1). For a single crystal and a given
, diffracted beams exist for specific orientations of the specimens according to equation (1). For
polycrystalline materials that include grains with random orientations, a large number of diffracted
beams appear in specific directions spread on cone surfaces defined by an angle 2 from the incident
beam. Their detection needs to use moving detectors or position sensitive detectors (linear detector or
2 dimension detector).
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The only parameter that can be easily changed, by using different anode materials, is  which is
related to the energy E of the X ray lines by the equation:
 = 1.24 / E
(2)
Here, E in keV corresponds to  in nm. Typical values are given in table 1.
Table 1: parameters for characteristic X ray emission & XRD
Anode
Energy
 nm

Energy
 nm

element
K line
K line
d = 0.2
L line
L line
d = 0.2
Cr
5.4 keV
0.229
35°
Co
6.93 keV
0.178
26°
Cu
8.05 keV
0.154
23°
Mo
17.5 keV
0.071
10°
2.29 keV
0.541
No diffr.
Ag
22.16
0.056
8°
2.98 keV
0.415
90°
W
59.3 keV
0.021
3°
8.4 keV
0.148
22°
for
for
Table 1 also reveals the geometrical limitations to collect the diffracted beams from lattice planes
separated by 0.2 nm, a distance typical for metals. Low energies do not give rise to diffraction because
the wavelength of X rays is too large compared to the crystal lattice parameter. High energies give
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small  values that are very convenient in transmission when using two dimension detectors. However,
in reflection which is a major requirement for in-situ XRD, high energies are not suitable because a
diffracted beam can exit the specimen only if 2 is larger than the angle of the incident beam to the
specimen surface.
For anodes made of W , a large emission spectrum exists with K line at 59.3 keV and L line at 8.4
keV (table 1); the latter can be used for XRD since it gives  values similar to those for Cu commonly
used for anodes. Indeed, we checked that the intensity of X rays for Cu-K are about twice the intensity
for W-L, in the same conditions (20 kV); this means that diffraction with W-L X-rays is possible with
laboratory XRD systems.
Typically, XRD is performed in reflection with the C2RMF laboratory system equipped with a Co
anode; diffracted beams are collected and currently interpreted for  between 5°and, at least, 30°
corresponding to d values covering all the crystalline materials of interest for heritage studies (table
2). In order to collect diffracted X rays for d=1nm, the incident beam angle to the surface must be less
than 10° (table 2), that is somewhat of a constraint (flat surface; small penetration of X rays).
In view of these geometrical constraints for reflection XRD (figure 1), an incident X ray beam at 14°
angle to an object seems reasonable in view of the expected roughness of its surface; the beam is then
spread by a factor of 4 on its surface. Only diffracted beams with  > 7° (2 > 14°) can be collected.
The best choices are between Cr and Co for K lines (table 2) and just before W for L lines (table 3),
viz. holmium or erbium if they were available for the fabrication of anodes.
Table 2
Energy
 nm

K line
K line
d = 1 nm
d = 0.2
d = 0.1nm
Cr
5.4 keV
0.229
7°
35°
No diffr
Co
6.93 keV
0.178
5°
26°
63°
Cu
8.05 keV
0.154
4°
23°
50°
70 µm
Mo
17.5 keV
0.071
2°
10°
21°
100 µm
Ag
22.16
0.056
1.6°
8°
16°
W
59.3 keV
0.021
0.6°
3°
6°
Energy



L line
L line
d = 1 nm
d = 0.2
d = 0.1nm
Mo
2.29 keV
0.541
16°
No diffr.
No diffr
Ag
2.98 keV
0.415
12°
90°
No diffr
Anode
for

for

for
Thickness for X ray
reduced by 100
20 µm
3 mm
Table 3
Anode
for
for

for
10 µm
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Ta
8.1
0.153
4.4°
22.5°
50°
W
8.4 keV
0.148
4°
22°
48°
Absorption of X rays must also be taken into account in the design of a XRD system. At small E
values, e.g. for Cr K line, only 30% of the intensity is transmitted in 400 mm of air or 400µm of mylar
and 65% is transmitted by 10 µm silicon. This gives limitations in the construction of the experimental
set-up : distances of the beam in air, materials for the various parts. In tables 2 & 3, we have reported
the thickness of lead glass (density: 3.7g/cm3, typical of glazes on ancient ceramics) to reduce the X
ray to 1% of the incoming intensity. For low energy X rays, the contribution of the first micrometers
below the surface is dominant for XRD, with a significant variation between Cr and Cu (table 2); at
the highest energies, materials are transparent to X rays; these conditions are usual for radiography.
The most common scheme for X ray powder diffraction is the Bragg-Brentano geometry (figure 1a). It
has many advantages (beam focusing on detector, corrections independent of , good detection of
minor phases, etc.). The source and the detector rotate around the specimen. Such a design can be used
for a portable in-situ XRD, although it may not be ideal because of complex mechanical construction
difficult to use in the field.
Parallel beam non focusing geometry (figure 1b) could be better for the examination of objects having
non planar surfaces. It is now widely used with synchrotron radiation. The aberrations acting in the
focusing mode (figure 1a) simply disappear in the parallel beam mode (figure 1b). This also allows for
an easy transition from the symmetric scan (2 to 1 coupling of the detector and the specimen) to the
asymmetric mode with constant incidence angle to the specimen. An additional advantage of the
parallel beam mode is that both reflection and transmission schemes may be equally performed in the
same system by rotating the specimen orientation from one position for reflection to another for
transmission. In our project, the parallel beam mode can be made using focusing devices for the X ray
tube that are commercially available.
Various types of portable XRD systems have been developed for different kinds of in-situ
observations:
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portable XRD for stress measurements in industrial environment (EPRI; Physique &
Industrie)
space instrument for XRD/XRF on Mars (MOXTEK tubes; B.Y.U.)
portable XRD/XRF for archaeological studies (Osaka University & Waseda University)
ASSING: this company has developed recently an equipment which is a portable adaptation of
the Bragg-Brentano parafocusing system. However, it is no longer on sale. A new version
should be introduced on the market by the end of 2005.
X ray fluorescence: sub-task 3.3
X ray fluorescence (XRF) requires X rays of widespread energies to excite as many as possible
electronic transitions to identify most elements. It is usual performed with anodes such as
molybdenum or silver and 30-50 kV voltages. The collected X rays come from a distance from the
surface limited by their absorption (see tables 2 & 3 for values ranging from 10µm to 100-500µm) for
accessible K lines. Because of their low energies, the X rays emitted by elements before silicon in the
periodic table are not accessible; indeed, they are generated in a small volume at the surface and they
are almost entirely absorbed at short distances in the air or helium atmosphere.
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Quantitative analysis can be performed if the specimens are homogeneous at the scale of the X ray
penetrations and if the geometrical configuration is reproducible for the various acquisition of data.
The detection limits are not a problem for the phase identification since XRD currently detects phases
above 5% in a mixture of crystalline compounds.
Conclusions on the portable system for in-situ XRF & XRD: sub-tasks 3.1 & 3.3
A number of characteristics have to be retained for the XRD/XRF system:
1- maximum weight of the order of 20 kg for air travel; this will probably be impossible to achieve.
Total weight of the various parts in the 50-70 kg seems acceptable for ground transportation.
2- analysis should be performed directly on the surface of objects (works of art in museums; walls in
monuments, etc.) and also on samples taken or fallen from the objects. The first condition requires
reflection mode. The second could give better results in transmission. It could be a separate system
operated in a van or a room nearby the working area; equipment such as X ray sources and detectors
can be shared.
3- materials to be examined are polycrystalline with grain sizes between 1 µm and several millimetres.
However, analysis must be performed on volumes sufficient to give meaningful information
(statistical averages, etc.).
4- The beam diameter should be of about 1 mm or less if a scan mode is incorporated to average the
signal collected on heterogeneous or large grain materials. Short distances between the system and the
objects are necessary, with a guarantee of no contact to prevent works of art from any damage.
5- the X ray source should allow XRF & XRD; it may require a movable monochromator for XRD
and XRF with a single tube. A focusing system (capillary optics) could be useful. An alternative is to
use two low power sources with different anodes that are commercially available in very light weight.
6- for X ray detection, the purchase of a 2 dimensional system has been decided, namely an “imaging
plate” system with a reading device weighing about 15 kg and small “plates”. The system will be
tested on a XRD temporary set-up in a near future.
7- the system will be comfortable to use:
- easy to set and align in the fields on objects with irregular surface (laser pointer; etc.)
- safe with respect to radiation dispersed in the environment
- data acquisition for one point should take a maximum of 30 min to one hour
- the procedure and computer interface should be accessible to all categories of scientists.
Experimentation: sub-tasks 3.1 & 3.3
An experimental set-up has been assembled in order to test the technical choices when they are done.
The set-up is based on a goniometric table that has been renovated. The source is a low power X ray
tube (MOXTEK, copper anode, 3 watt, natural cooling, total weight of less than 1 kg). A silicon drift
detector (SDD Roentec) is used with no selection of energy. The alignment of the source, specimen
and detector is performed using the detector, standard phosphor screens being inefficient at the low X
ray intensity of the source. We have purchased a camera (marCAM; 2200 euros) which gives a 20 fold
magnification on a TV monitor, but it does not bring a significant improvement in sensitivity.
Rotations and translations of the source as well as of the detector are provided to achieve the
alignment.
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A modern floor tile has been used as a specimen to check the facility to obtain a diffraction
Figure 2: X ray diffraction peak taken from a modern ceramic tile, obtained with a preliminary
experimental set-up. The peak corresponds to the inter-planar distance d = 0.34 nm in quartz.
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15
10
Série1
5
0
26 000
26 500
27 000
27 500
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peak. The acquisition was made with 0.01° angular steps and step time of 2 sec; these are fast
conditions for acquisition. The results is shown in figure 2 where the most intense peak of quartz has
been detected. The curve is noisy and weak (maximum of 20 cps), but the peak is reasonably narrow
(about 0.2°). By comparison, with a commercial X ray apparatus we found at the maximum of the
peak 300 cps with a noise about 5 cps. The conditions of our acquisition (figure 2) have to be
optimised, a task to be performed in the near future.
The diffraction result in figure 2 has been obtained with a classical mechanical system and a low
power Cu tube; the only monochromator is the specimen itself according to equation (1) since we did
not select the energy corresponding to the Cu-K line. In such geometry, the diffracted beams are
monochromatic and dispersed in angle. It is the geometry that we plan to use for the XRF & XRD insitu portable system.
Based on results from the literature, we have ruled out the possibility of using energy dispersion X ray
Diffraction (ED-XRD). This is a direct application of combined equations (1) and (2) where  is fixed;
polychromatic X rays are used. Both fluorescence and diffraction peaks are superimposed on the same
diagram. The intensity of the former being generally superior to that of the latter, it may be difficult to
identify the phases in multi-component systems. However, in order to fully justify our choice, we plan
to perform XRD experiments on the same specimens and obtain quantitative information on the
differences between ED-XRD and angular dispersed diffraction.
Task execution summary: work, meetings, expensess etc.
Work
The programme started on the 1st of June 2004 and the work was “kicked off” in Florence on the 16th
and 17th of July 2004. The C2RMF team has been formed; it includes ten persons from the C2RMF
CNRS UMR 171 that will spend a fraction of their working time on the project. A post-doc has been
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actively searched; a well adapted candidate has been found and joined the team at the beginning of
april 2005.
Sub-contracting
The core part of the work is to design the best system to control the X ray incident and diffracted
beams. A number of consultations have been made with various scientists. The design of optics for X
rays cannot be carried out in the CNRS-C2RMF laboratory without the assistance of an expert group.
This was named “sub-contracting” in the EU-ARTECH project as planned in the JRA2 task 3
section.
The “laboratoire de cristallographie, CNRS UPR 5031 Grenoble” is the ideal partner to collaborate in
the technical choices in the handling of the X ray beams. However, it is not possible to establish a
“subcontracting” contract between two laboratories belonging to CNRS, viz. UMR 171 and UPR
5031. Terms of agreement have been made between the two parties to organise the technical activities.
The CNRS-C2RMF will have the entire financial responsibility and, therefore, spend the subcontracting budget according to the needs of the collaborative work with CNRS UPR 5031.
The team involved in the project in the CNRS UPR 5031 is includes six persons, each dedicating a
fraction of his time to the project.
Meetings
In order to organise the work and focus the activity of the teams on the various sub-tasks, several
meetings took place on the 10th of september 2004 in Paris, 13th of October 2004 in Grenoble, 24th of
january in Paris, 16th of february in Paris and 9th of march in Grenoble. Minutes of the meetings (in
french) are available.
The various EU-ARTECH meetings were attended by members of the team: july 16, 2004 kick-off
meeting by MM & JC; january 13-15, 2005 interim meeting in Amsterdam by MM, JC & JS, and may
26-28, 2005 first annual meeting in Ormylia by MM & JC. Each time, the advancement of the work
has been presented.
Expenses
In addition to the costs corresponding to the above mentioned meetings and travels, a number of
expenses have been made to develop experimentation to help in the technical choices for the
XRD/XRF system. They include basic equipment such as digital analogue converters, data processing
systems, etc.. We mention the major expenses:
- first, a CCD camera with a X ray to visible light converter screen (2200 euros)
- second, a specific analyser for the diffracted beams has been chosen (cost 10000 euros). It is in the
process of being purchased and, when delivered in July 2005 (or later, the rate controlling step being
the management rules), its performances will be studied in the “laboratoire de cristallographie, CNRS
UPR 5031 Grenoble”.
- third, a 2-dimension detection has been chosen (cost 18000 euros); it consists of “imaging plates”
that has been delivered in may 2005. The first tests will be performed in CNRS UMR 171 Paris with
the experimental set-up adapted for that purpose. It will then be evaluated in CNRS UPR 5031
Grenoble together with the analyser.
Other pieces of equipment purchased by the C2RMF CNRS UMR 171 have been used in the
experimentation for the first year of the research (X ray sources, detectors, mechanical devices, …);
their values is about 40 keuros.
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