It is well known that the content of trace elements present in archaeological pottery can give information on the artefacts provenance. Today, their absolute determination is obtained by using non-destructive portable XRF spectrometers for "in situ" applications. However, the compact x-ray tubes largely used as excitation source, can be subjected to intensity and energy fluctuations and frequent recalibrations of the systems are required in order to maintain the quality of the data. In the present work the BSC-XRF spectrometer (Beam Stability Controlled XRF), realised at the LNS/INFN laboratory of Catania in the framework of the Agenzia2000 Project of the Italian CNR, has been used for the non-destructive quantitative determination of some trace elements (Rb, Sr, Y, Zr and Nb) in 50 fine ceramic sherds. The BSC-XRF spectrometer is equipped of a system to monitor the energy and intensity stability of the excitation beam emitted by an x-ray tube. The control of the stability is not an electronic device operating on the applied high voltage and on the current. It consists on a direct intervention on the beam through suitable parameters obtained from the fluorescence emitted by a double Ag/Ba thin target arranged in transmission mode. In order to determine the best experimental conditions of the system, a preliminary calibration has been performed and a stability operating region has been fixed. By using this single calibration it is possible to operate along the time reproducible measurements even if unstable and economic x-ray tubes are used for the measurements. The absolute concentration of Rb, Sr, Y, Zr and Nb has been determined in 50 pottery sherds by using a method based on a multi-linear regression approach developed at the LNS/INFN laboratories. The analytical procedure has been previously tested by using different petrologic standards; the average deviation between certified composition and the XRF quantitative data is less than 10%. It could be observed that the XRF technique is a surface method and a quantitative determination is meaningful only when the material being analysed is homogenous. In order to test the homogeneity of the material composing the analysed samples, a small portion (less than 1 gr) of 10 sherds has been powdered, carefully homogenised and pressed to a disk-shaped pellet. The powdered pellets have been measured both with the BSC-XRF system and quantitatively analysed by using the above mentioned method. Additionally, quantitative results have been compared with those obtained by a chemical analyses of the same powders. Destructive and non-destructive data are in agreement within the 10-15%.
Quantitative non-destructive determination of trace elements in Archaeological pottery by using the Portable BSC-XRF (Beam Stability Controlled XRF) spectrometer of the LNS/INFN Laboratory
Romano FP;Pautasso A
2004
Abstract
It is well known that the content of trace elements present in archaeological pottery can give information on the artefacts provenance. Today, their absolute determination is obtained by using non-destructive portable XRF spectrometers for "in situ" applications. However, the compact x-ray tubes largely used as excitation source, can be subjected to intensity and energy fluctuations and frequent recalibrations of the systems are required in order to maintain the quality of the data. In the present work the BSC-XRF spectrometer (Beam Stability Controlled XRF), realised at the LNS/INFN laboratory of Catania in the framework of the Agenzia2000 Project of the Italian CNR, has been used for the non-destructive quantitative determination of some trace elements (Rb, Sr, Y, Zr and Nb) in 50 fine ceramic sherds. The BSC-XRF spectrometer is equipped of a system to monitor the energy and intensity stability of the excitation beam emitted by an x-ray tube. The control of the stability is not an electronic device operating on the applied high voltage and on the current. It consists on a direct intervention on the beam through suitable parameters obtained from the fluorescence emitted by a double Ag/Ba thin target arranged in transmission mode. In order to determine the best experimental conditions of the system, a preliminary calibration has been performed and a stability operating region has been fixed. By using this single calibration it is possible to operate along the time reproducible measurements even if unstable and economic x-ray tubes are used for the measurements. The absolute concentration of Rb, Sr, Y, Zr and Nb has been determined in 50 pottery sherds by using a method based on a multi-linear regression approach developed at the LNS/INFN laboratories. The analytical procedure has been previously tested by using different petrologic standards; the average deviation between certified composition and the XRF quantitative data is less than 10%. It could be observed that the XRF technique is a surface method and a quantitative determination is meaningful only when the material being analysed is homogenous. In order to test the homogeneity of the material composing the analysed samples, a small portion (less than 1 gr) of 10 sherds has been powdered, carefully homogenised and pressed to a disk-shaped pellet. The powdered pellets have been measured both with the BSC-XRF system and quantitatively analysed by using the above mentioned method. Additionally, quantitative results have been compared with those obtained by a chemical analyses of the same powders. Destructive and non-destructive data are in agreement within the 10-15%.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
