1,721,378 research outputs found
Radiation applications in art and archaeometry : X-ray fluorescence applications to archaeometry : possibility of obtaining non destructive quantitative analyses
No full textThe possibility of obtaining quantitative XRFanalysis in archaeometric applications is considered in the following cases:
(i) Examinations of metallic objects with irregular surface: coins, for instance.
(ii) Metallic objects with a natural or artificial patina on the surface.
(iii) Glass or ceramic samples for which the problems for quantitative analysis rise from the non-detectability of matrix low Z elements.
The fundamental parameter method for quantitative XRFanalysis is based on a numerical procedure involving he relative values of XRFlines intensity. As a consequence it can be applied also to the experimental XRFspectra obtained for metallic objects if the correction for the irregular shape consists only in introducing a constant factor which
does not affect the XRFintensity relative value. This is in fact possible in non-very-restrictive conditions for the experimental set up.
The finenesses of coins with a superficial patina can be evaluated by resorting to the measurements of Rayleigh to Compton scattering intensity ratio at an incident energy higher than the one of characteristic X-ray. For glasses and ceramics the measurements of the Compton scattered intensity of the exciting radiation and the use of a proper scaling law make possible to evaluate the matrix absorption coefficients for all characteristic X-ray line energies
The role and the limits of scientific non destructive physics methods in art and archeology
No full textAntonino M. Milazzo, Dimensione retorica e realtà politica. Dione di Prusa nelle orazioni III, V, VII, VIII, 2007
No full textGangloff Anne. Antonino M. Milazzo, Dimensione retorica e realtà politica. Dione di Prusa nelle orazioni III, V, VII, VIII, 2007. In: L'antiquité classique, Tome 78, 2009. pp. 299-300
Evaluation of effects of irregular shape on quantitative XRF analysis of metal objects
No full textQuantitative XRF analysis of metal alloys can be obtained by using the general fundamental parameter method based on the comparison of x-ray line fluorescence intensities with those obtained from reference standard pellets in identical experimental conditions. Corrections for auto absorption and secondary excitation effects are fundamental to obtaining quantitative results.
When analyzing a real object with irregular, or at least nonpellet-shaped, geometry and/or of incorrect positioning, an additional correction factor for x-ray fluorescence line intensities must be entered.
In this paper we review the problem of the contributions to the error specific to an irregular surface or incorrect positioning intrinsic to the fundamental parameter method, in the more enlarged context of considering a real experimental setup in which irradiation and detection angles are not exactly constant, as assumed in the fundamental parameter method. They are accounted for by the corrective irregular shape factors.
In principle, these factors must be separately calculated for each value of excitation and characteristic x-ray energies, and the relative precision in the quantitative determination of elemental concentrations with the fundamental parameter method can be estimated from the relative amplitude of the variation of shape factor values depending on the exciting energy spectrum. One obtains the result that the correction due to irregular shape or incorrect positioning of the object under examination tends to the limit 1, or, more generally, to a constant value independent of the excitation and emission x-ray energies in the limiting case where the direction of the exciting radiation coincides with that of the detected fluorescence x-rays.
The results of calculations of the relative precision of XRF quantitative analysis are shown for gold-based alloy objects in some specific cases of surface roughness and positioning of the object. Dispersion around the nominal values for the angles of incoming and outgoing x-ray directions is assumed as determined by the geometric conditions in two selected instrumental setups. A nominal value of 45 degrees was assumed for both the angles in the first case. In the second case, we considered an irradiation setup where the condition of coincidence for incoming and outgoing x-ray directions is nearly achieved by employing an annular silicon drift detector (SDD) with a central hole, which allows the passage of the exciting x-rays.
An interesting result obtained in the latter case is that, looking only at the dependence on the irregular shape, an attainable precision on the order of < 1%o can be achieved.
In view of the possible applications of quantitative XRF analysis to jewellery, employing SDD detectors capable of very high counting rates should allow a statistical error under the above-mentioned limit in a reasonably short measuring time.
However, concerning the error deriving from intrinsic x-ray tube instability, an investigation aimed at achieving a stable enough system is still needed
Physics methods in archaeometry
No full textProceedings of the International School of Physics "Enrico Fermi", Course CLIV, Varenna 17-27 giugno 2003. The volume collects the contributions of several world leaders in the field of archaeometry
Evaluation of evaporation flux in building materials by infrared thermography
No full textThe presence of water inside the walls can be considered one of the most important causes of degradation in historical buildings. This is particularly due to evaporation which can give rise to salt deposits inside the superficial pores. Evaporation flux from wall surfaces can be estimated quantitatively by measuring the temperature which depends in a sensitive way on the evaporation rate. At equilibrium condition among all the different kind of heat exchange the wall temperature depends essentially on the evaporation rate and the thermal properties of the material (porosity, conductivity).
In the Archaeometry lab of “Istituto di Fisica Generale Applicata” we performed some experiments on several brick, plaster and stone specimens with different porosity in order to obtain different evaporation rates. We employed a climatic room where environmental parameters (temperature, RH, ventilation and irradiation) are controlled and cooling effects due to evaporation are investigated by a SW IR thermographic system in steady conditions in order to understand the relation between evaporation flux (), water content (Wc) and surface temperature (Ts).
Table of comparative values of these three variables (, Wc, Ts ) were obtained for several materials and applicability limits of the thermographic technique for moisture detection are discussed
Analisi di provenienza di ceramiche dal sito di piazza Marconi a Cremona
No full textInformazioni sulla provenienza di reperti fittili possono essere ottenute indirettamente a partire dai dati sulla composizione elementare. Infatti la conoscenza della composizione chimica, con particolare attenzione a quelli cosiddetti minori o addirittura in tracce, è direttamente legata a quella della materia prima utilizzata.
Sono stati analizzati con la tecnica EDXRF in modo rigorosamente non distruttivo circa cinquanta frammenti ceramici (II sec. a.C.) provenienti dallo scavo di piazza Marconi a Cremona, oltre a campioni di riferimento provenienti da Adria, Volterrra, Arezzo e Cremona.
La determinazione della provenienza è stata effettuata con tecniche di analisi multivariata: in particolare, PCA e Cluster Analysis
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