LIBRA: The Ion-Beam Applications Program

INP's activities on Ion-Beam Applications

The INP group has a long-term expertise (since mid 70's) in the development of analytical techniques based on nuclear methodology and instrumentation often combined with X-Ray spectrometry. These activities are related to cultural heritage, biomedicine, and environmental studies.  

 

In the field of cultural heritage, the activities of the group include:

 

Development of a novel micro-analytical technique known as 3D Micro-PIXE. This technique was first applied in vacuum in the framework of a joint experiment at the Micro-Analytical Center of Jožef Stefan Institute in Ljubljana, Slovenia. It was then employed under atmospheric pressure in a subsequent experiment (March 2007) using the external proton micro-beam of the AGLAE accelerator at the Centre de Recherche et de Restauration de Museés de France, Paris, France. The latter activity was supported by the FP6/Eu-ARTECH trans-national access program.

  • Development and application of an external ion-beam set-up for non-destructive analyses.

  • Development of an external ion-beam end-station for the combined implementation of the PIXE, RBS and PIGE techniques.

  • Development, evaluation and application of portable X-Ray Fluorescence (XRF) instruments for the non-destructive analysis of cultural materials.

  • Development of analytical methodologies and standardization procedures to improve the quality of the analytical information obtained by ion-beam and X-Ray Fluorescence techniques

  • Performance evaluation studies of tagging technologies. These are often applied to ensure the identity of replicas or the authenticity of original objects/artworks using ion-beam technologies.

  • Application of XRF to non-invasive advanced characterization of ancient or historical artifacts/artworks and diagnosis of the state of preservation of artifacts exhibited at the museum showcase or storehouse in order to support conservation treatments.

  • Application of Nuclear Reaction Analysis (NRA) for elemental depth profiling (depth profile of a) sulfur and copper in artificially prepared patina layers and b) hydrogen and sodium in ancient glass).

  • In addition to these activities, the INP group has developed an advanced and unique expertise in surveying in-situ monuments (such as funeral tombs) as well as archaeological collections comprising metallic objects, ceramics, painted plasters, and polychromic marbles. This expertise was demonstrated in different museums and archaeological sites across Greece, including: Ancient Messene, the Nestor ‘”Palace” in Messenia, Ancient Korinth, Archaeological Museum of Nauplio city, National Archaeological Museum in Athens, Delos, Museum of Vergina, Macedonia, Greece etc. The INP group has, furthermore, implemented a state-of-the art trans(portable) micro-XRF spectrometer in surveying ancient or historic metal artefact collections across the Mediterranean region including the Armoury palace in Malta, the Damascus archaeological Museum in Syria, Numismatic Museum at the Yarmouk University and from the Umm Qais site in Jordan and others. Some of these in-citu analyses are shown in figure 3 below. These research activities have also been accompanied by technology transfer to end-users, through the organizations of training courses for conservators and the development of dedicated large-beam mobile XRF spectrometers, notably for the Greek Ministry of Culture (Stone conservation Centre and Archaeological Museum of Volos), the Benaki (private) Museum in Athens, the Institute of Materials Science of NCSR “Demokritos”, and others.

In the field of environmental research, the activities of the INP group included:

  • Chemical state analysis of samples employing sub-natural line-width resolution PIXE measurement of the Kα diagram line. The work was performed in the framework of a Greek-Slovenia bilateral collaboration (2001-2003), by implementing PIXE in combination with a high-resolution crystal spectrometer in Johansson geometry. The technique developed enables energy resolution below the natural line-width of the ion-induced Kα diagram lines of the elements. The potential of the analytical methodology developed in chemical speciation studies was demonstrated via the speciation of sulfur in an aerosol filter.

  • A complete systematic study of the concentrations of all inorganic elements contained in Greek lignite and fly ash. This study was performed in the framework of the European program CI1*-CT91-0858 “Trace elements in coal”. The analysis of fractionated fly ash samples and individual fly-ash particles revealed for the first time, interesting information about the distribution of toxic trace elements in fly ash particles of small size.

  • Systematic measurements of the concentrations of about thirty-five inorganic elements in a large number of soil samples from the area of the old (now closed) Athens airport. These measurements were performed on behalf of the Hellenic Ministry for the Environment, Physical Planning and Public Works, using XRF and ion-beam analytical methods. They aimed at the assessment of the toxicity level of the area (possibly caused by its earlier use by aircrafts and related services) in view of its future use as a a residential park. In this framework, an analytical technique based on Deuteron Induced Gamma-ray Emission (DIGE) was developed and applied at the Tandem accelerator of INP enabling the determination of beryllium in geological samples.

In the field of biomedice, the activities of the INP group have, so far, focussed on the development of novel analytical methods aiming at determining trace elements in human tissues or fluids through efficient, precise and accurate application of energy dispersive fluorescence (ED-XRF) and ion beams. The following characteristic examples are, hereby, reported:

  • Determination of uranium in human urine by applying a pre-concentration method resulting in detection limits competitive with alpha spectrometry that is suitable for controlling uranium uptake by human above the normal threshold levels.

  • Determination of low-trace platinum levels in the blood circulation of mice after its administration either via aqueous cis-platin solution or in the form of Pt nano-particles.

  • Trace element metabolic studies in patients being in various stages of renal failure.

  • Development of a database including representative trace element concentrations for blood, serum and plasma of the Greek population.

  • Application of Proton-Induced γ-Ray Emission (PIGE) for fluorine analysis in teeth and beryllium analysis in dental alloys.

Apart from the research activities described above, the INP group has also been collaborating with almost all Greek universities and other research centers. Research groups from the National Technical University of Athens (NTUA), the National University of Athens (UoA), the Aristotle University of Thessaloniki (AUTH), the University of Ioannina (UoI), as well as from the Institute of Materials Science (IMS), the Institute of Microelectronics (IMEL) and the Institute of Nuclear Technology and Radiation Protection (INT-RP) of “Demokritos” and, recently, groups from the National Hellenic Research Foundation (NHRF) and the University of Crete (UoC) are performing joint experiments with the INP group at the INP Tandem accelerator to a) study properties of materials of technological interest subjected to irradiations, b) test the response of detectors, some of which are used in high-energy physics experiments, to high-dose charged-particle and neutron irradiations, c) measure cross sections of charged-particle induced reactions applied in material analysis, d) analyze materials for nuclear waste applications,  e) measure neutron-induced reaction cross sections for ADS systems (within the n_TOF collaboration) and f) perform atmospheric-pollution related analyses. These joint activities have been documented by a significant number of collaboration papers. A detailed description of these activities is beyond the scope of the present presentation.   [top] [relevant publications] [theses]

LIBRA activities in Ion-Beam Applications

  • Acquisition & Installation of a micro-beam system at the Tandem accelerator.

The development of the low energy particle micro-beams in the mid-eighties opened a new era for the analytical ion-beam techniques. The possibility of extracting information over a microscopic region of the material under investigation revealed new potential for advanced analytical studies.  Particle micro-beams are formed as an ion-beam passes through strong focusing fields produced by quadrupole lenses. Since one quadrupole lens can focus in one plane only, a sequence of them (at least two) is needed for an overall beam focusing to be realized. Several types (electrostatic, magnetic) and arrangements (from doublets to quintuplets) of quadrupoles have been studied and tested over the years aiming the formation of smaller and more intense beams. Furthermore, the evolution of micro-beams brought powerful characteristics like the fast scanning mode which apart from the two-dimensional expansion for the already existing conventional techniques (PIXE, RBS), led to the establishment of new analytical techniques like the Secondary Electron Imaging (SEI) and the Scanning Transmission Ion Microscopy (STIM). For the effective use of the characteristics and the potentials provided by micro-beams, the nuclear microprobes setups had to be built. These setups combine a group of detection systems (for X-rays, particles, γ-rays, electrons, UV, etc.) placed in an optimized geometry for simultaneous operational functionality. Furthermore, sample positioning systems with sub-micrometer accuracy, fast electronic circuits, high stability power supplies and sophisticated software for the real-time data analysis and imaging/mapping representation have also been included and play a crucial role in enhancing the capabilities of the microprobe. All these enable the effective combination of several ion-beam techniques towards the solution of a given analytical problem with more accuracy and reliability. Nowadays, after more than 25 years of efforts and development, the fast, accurate and non-destructive ion-beam micro-analysis of samples with elemental microstructure can be easily realized. The micro-ion beam techniques (PIXE, RBS, STIM, SEI, etc.) are well established and they are considered as routine procedures for solving analytical problems for biomedicine, environmental research, material science, cultural heritage etc. At the same time, they are still today expanding in many more scientific fields, while the machines can now provide ion-beam dimensions below 1 μm with more than 100-200 pA, making the study of even smaller structures more feasible than ever.

    Biomedicine is the major application field for the low energy micro-beam techniques. The light elements-based biological tissues permit micro-PIXE combined with STIM/RBS to provide accurate quantitative information (at the ppm level) of important trace elements (Al, Ti, Ca, Fe, Cu, Zn etc.). Furthermore, through the elemental mapping procedure some dominating biochemical processes can be revealed, proteins, molecular clusters, etc. All these analytical possibilities make micro-ion beam techniques the only tool for elemental analysis with spatial resolution in the sub-cell scale.

    Environmental research is another important application with a continuously growing demand among the particle micro-beam facilities. Elemental and structural analysis of aerosol samples collected by impactors is the major analytical procedure for the atmospheric quality evaluation and control, especially in big modern cities, infrastructure areas, ports etc. A particle micro-beam can identify and analyze individual particles down to sub-micrometer dimensions revealing pollution sources of toxic elements that can be inhaled directly by human beings and accumulate into the lungs.

    Cultural Heritage research and applications have also been supported by particle micro-beam facilities, especially in countries with rich cultural heritage. We mention here the AGLAE accelerator in Paris, France and the accelerator of LABEC in Florence, Italy, as examples. These installations can be considered as dedicated particle micro-beam facilities that offer state of the art services in cultural heritage. Greece is certainly one of the European countries with a rich cultural heritage deserving a state-of-the art micro-beam facility, to perform not only cultural heritage studies, but also forefront research in the domains described above.

  • Development of a novel confocal micro-PIXE set-up.

The potential of ion beam methods to provide full characterization is significantly hampered by the fact that materials often exhibit inhomogeneities or a layered structure extending far below the surface. Several important attempts have been reported, that aim at providing analytical methods for depth resolved analysis. So far, all these efforts use PIXE analysis at variable incident energy or variable projectile impact angle. The strong dependence of the X-ray ionization cross section on the proton energy, as well as the possibility to vary continuously the proton energy and subsequently the range of protons in matter, may result in the successive tuning of the average PIXE-production depth deeper inside the analyzed material. These fundamental physical properties triggered and motivated the development of the so-called differential PIXE analysis. Since 1996, various analytical strategies have been developed and implemented by different groups. In 2003, a confocal arrangement of X-ray optics for three-dimensionally resolved Micro X-ray fluorescence spectroscopy (Micro-XRF) was developed by the TU Berlin group of B. Kanngießer. Hereby, two X-ray optics, one in the excitation path of the sample and the other one in front of the detector, define a probing volume from which the information on the quantitative and qualitative elemental distribution in the sample is collected. By moving the sample through this probing volume, depth resolved measurements can be carried out. Hence, with this new arrangement Micro-XRF is rendered a depth sensitive method and, finally, with the already existing mapping capabilities, evolves into three-dimensional resolving technique in the micrometer regime. Successful applications of this new 3D Micro-XRF method have been reported in the field of cultural heritage, as well as in other disciplines. The main objective of this task is to transfer the confocal concept of geometry to Micro-PIXE analysis with the same aims: to obtain depth resolution in the micrometer regime and to measure three-dimensionally resolved elemental distribution in a sample. This would enable depth resolved measurements in comparison to differential PIXE, where a variation of the angle or even of the energy of the proton beam is necessary. The implementation of the confocal geometry at an ion-microprobe beamline has certain advantages with respect to 3D Micro-XRF set-ups, recently installed in many synchrotron facilities. For 3D Micro-PIXE, only one X-ray lens in front of the detector is required taking advantage of the excellent intrinsic spatial resolution of the ion microprobe. Also the beam scanning possibilities play an important role not only for the relative simple and fast alignment of the confocal set-up, but also for deducing faster depth intensity profiles with advanced precision. A decrease of the proton ionization cross sections with increasing depth, in contrast to the fluorescence cross sections which are depth independent, is certainly a disadvantage and a limiting factor as far as the range of depth analysis is concerned. On the other hand, higher proton energies (greater than 3 MeV) and relative low atomic number matrices (organic, aluminum-silicate) increase the penetration depth of protons to more than 100 μm, thus, improving the information depth for elements emitting characteristic X-rays at energies above ~5 keV. 3D-Micro-PIXE seems to be a very promising technique for depth- resolved analysis and elemental analysis with 3D resolution, which has to be further exploited, both theoretically and experimentally. In particular, due its non-destructive and depth-resolving properties, 3D Micro-PIXE under vacuum or even better under atmospheric conditions seems especially suited for investigations in the field of cultural heritage.

 

The task of the INP group within LIBRA project for further development of 3D Micro-PIXE technique and its applications will be focused on new research directions.

  • Development of 3D Micro-PIXE quantitative analysis. Using an analytical description for the energy dependent spatial response function of the X-ray lens at the focal region and incorporating together the beam profile, the probing-volume will be analytically described through a sensitivity function expressed in spatial coordinates. Particle induced X-ray intensities will be calculated taking into account all the well known processes that are involved in the PIXE process (ionization, stopping power, and self-attenuation) and through convolution with the sensitivity function, 3D Micro-PIXE intensities can be simulated.

  • Experimental realization of 3D Micro-PIXE at the Tandem Accelerator of INP. First applications will be presented in the fields of the cultural heritage and environmental science. In both cases, the inherent advantages of 3D Micro-PIXE together with the unique possibilities of the Demokritos TANDEM accelerator (available proton energies up to 10 MeV), will offer advanced characterization capabilities. Preliminary investigation of 3D Micro-PIXE (unpublished work) shows a powerful potential to provide full elemental characterization of particulate matter in aerosol PM10 filters, namely, 3D elemental analysis of individual particles.

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Upcoming LIBRA scientific events in Ion-Beam Applications

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Past scientific events in Ion-Beam Applications organized by the INP Group

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LIBRA Seminars in Ion-Beam Applications

A series of seminars will be organized during the course of LIBRA. A list will be given here soon.

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Other Worksops and Conferences of relevance to LIBRA research 

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Ion-Beam Applications


Contact

Dr. Sotirios V. Harissopulos
Tandem Accelerator Laboratory,
Institute of Nuclear Physics,
NCSR "Demokritos",
POB 60228, 153.10 Aghia Paraskevi,
Athens, Greece
sharisop@inp.demokritos.gr