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Fundamental Parameters W.G.

An international initiative on establishing accurate critical data for interactions of X-rays with matter (“fundamental parameters”)

Accurate critical data related to the interactions of X-rays with matter (“fundamental parameters”) are required for the whole range of applications, and the lack of recent reliable values with low associated uncertainties was pointed out during the last European X-Ray Spectrometry conference (EXRS2008) held in June 2008 in Cavtat (Croatia). Thus, within the framework of the European X-ray Spectrometry Association (EXSA), a common initiative was proposed by Physikalisch-Technische Bundesanstalt (PTB, Germany), LNE/Laboratoire National Henri Becquerel (France) and Technology University Wien (Austria) to start an international initiative to assess/evaluate the available data and, based on the evaluation results, to establish new accurate critical data with reduced relative uncertainties for interactions of X-rays with matter. As the most promising approach for this purpose, dedicated experimental determinations of selected fundamental parameters of interest combined with interpolations between these values by means of theoretical values derived by new calculations has been identified.

The main motivation for such initiative is to overcome the partially poor quality and incompleteness of current x-ray fundamental parameters which constitute a serious limitation for further progress of X-ray technologies. Pushing the limits of X-ray technology requires critical assessment and evaluation of available data and determination of precise x-ray fundamental parameters with reduced relative uncertainties.

Such accurate data are needed for the whole range of applications, including:

- Medical technology: implant coatings, tomography, imaging (non-invasive diagnostics and therapy - minimizing the impact of radiation doses on human health)
- Nanotechnology R&D related analysis, quality control
- Renewable Energy, advanced materials for photovoltaic
- Environmental control: fine dust analysis, aerosols, waste water, soils
- Recycling: irregularity shaped objects requiring reference-free methods
- Materials analysis: safety issues, cultural heritage,
- Law enforcement (RoHS, forensic,..).

Three National Metrology Institutes (Physikalisch-Technische Bundesanstalt, Germany; National Institute of Standards and Technology, USA and LNE/Laboratoire National Henri Becquerel, France), several research institutions and industrial companies are involved in this action. Participants are gathering in workshops to discuss the relevance of fundamental parameters (FP) in X-ray technology and applications, the status of FP compilations, and the present state of the art in related theory. Discussion between the participants concerns prioritization of FP, i.e. what parameters are most important (among attenuation and absorption coefficients, fluorescence and Auger yields, Coster Kronig transitions, scattering cross sections, transition probabilities, electron ionization cross sections, elastic and inelastic scattering cross sections, X-ray tube spectra, detector response function, line shapes) and state of the art in measurement (detectors, high resolution spectrometers, electron spectrometers, calibrated detectors, electron sources, SR monochromatic, available materials and characterization) and theoretical calculations. Six expert groups are working on specific aspects like:

- Prioritization of FP requirements (energies, elements, uncertainties),
- Experimental facilities (need for improved instrumentation),
- Theory & codes – challenges: competent use and update of existing software,
- Compilations (need for new strategies), data processing,
- Definition of technical terms (National Metrology Institutes),
- Establishment of common data base accessible to the public.

The first roadmap resulting from the work of the expert group can be downloaded here: IIFP_Roadmap_V1.pdf

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