LABORATORY: CNR ISPC – XRAYLab

 

NAME OF THE INSTRUMENT

Diffrattometro a raggi X sviluppato da XRAYLab 

 

GENERAL DESCRIPTION

Different mineralogical phases can be identified via X-Ray Diffraction (XRD). Differently from element-specific analytical methods (such is the broadly used XRF), XRD provides information on the nature and structure of chemical compounds (even if present in complex mixtures).

Given the crystallinity found in different types of antics materials, XRD is particularly suited for investigation of many archeological and historical-artistic samples. Its application is especially fruitful in the identification of the nature of pigments and their degradation products in paintings realized on any support (wood panels, papyrus paper, frescoes, murals) as well as the study of corrosion and degradation surface layers.

The mobile XRD system developed within the XRAYlab of ISPC is applied on polycristalline sample and employs a parallel beam. This set up has the great advantage, compare to traditional XRD systems, of keeping fixed in position both the sample and the Xray source, while the Bragg angular scan is obtained by moving the detector alone. In this fashion, accurate diffraction patterns are collected since there are less opportunities to introduce angular shifts and the angular resolution improves.
This is a not destructive method and there is no need for any sample preparation. Optimal cases of application are: paints on any substrate, patinas of corrosion and deterioration.

 

TECHNICAL DESCRIPTION

The XRD system developed within the XRAYlab of ISPC is a modular mobile system optimized for in-situ operation. The system is composed of a measurement head equipped with a 30W Fe target microfocus X-ray source coupled with a polycapillary optics for parallel beam with spot on the investigated sample of about 600 micron. in situA Si-PIN detector is used for the collection of the diffraction pattern emerging from the samples. A digital filter acts on the DXP (Digital X-ray Processor) of the processor to select the wavelength (ie the energy) of which visualize the diffraction - typically K-alpha line of the tube anode material. During each measurement it is possible to acquire simultaneously both the XRD pattern and the XRF spectrum for the same measurement point.

The X-source and the detector operate on a mechanical goniometer of theta-theta geometry, with radius of 15 cm. The parallel X-ray beam is kept at a fixed angle of ~10 deg along the goniometer (ie the source tube is not moved), while the detector automatically scans angular position between 12 and 70 deg, from the opposite end of the goniometer. The sample is positioned outside the goniometer rail, at its geometrical center (ie at distance of ~15 cm from all points of the rail). Precise alignment of the sample is gained through a two-lasers pointing system.

During measurement, the whole diffractometer head is held by a tripod that keeps the system in position relatively to the investigated sample area. The sample needs to be held vertically on either a support or hang on a wall. Each XRD point measurement takes approximatively 30 minutes.

 

Referent

Paolo Romano  francescopaolo.romano@cnr.it

 

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