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Play a game: Just mach spectra to materials

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Play a game: Just mach spectra to materials

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http://LearningApps.org/watch?v=pct1wo5yt16

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https://kaiserscience.wordpress.com/physics/electromagnetism/light-is-an-em-field/

https://courses.candelalearning.com/colphysics/chapter/29-3-photon-energies-and-the-electromagnetic-spectrum/

P. Craddok,  Science Investigation of  copies, fakes and forgeries, 2009 Elsevier

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Photoelectric effect and the X-Ray lines

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Photoelectric effect and the X-Ray lines

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-about XRF

-typology of investigation

-ND techniques: some examples

-some techniques that employ X-Rays

-physics principles

-photoelectric effect

-coeherent and incoherent scattering

-XRF - the method

-application to Cultural Heritage artwork

-experimental set-up

-polycapillary optics

-measurment geometry

-the measurment (video)

-XRF spectrum

-limits

-Bibliography

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Here is the operating device at INFN_LNF

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The XRF spectrum is a plot where on the x-axis the energy of the photons emitted by the sample is reported versus the counts (the number of photons emitted at a given energy) on the y-axis. The peak's position, respect to the energy, permits to identify the element present in the sample. The peak's area is directly correlated to the concentration % of the element in the examined specimen.

In the following figure, the XRF spectrum of a denarius issued by Nero (sample 253568) is reported.

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-it is a surface analysis

(depending on matrix composition the analyzed layer rang from few microns to some cm)

- chemical elements with Z<13 not detectable

- detection limits for each element are directly correlated to matrix composition, exciting energy and beam intensity

- energy resolution of the detector

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Denarius 253568 Roma 66 DC

(Museo Archeologico Nazionale di Firenze)

http://www.archeotoscana.beniculturali.it/index.php?it/146/firenze-museo-archeologico-nazionale

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Application to Cultural Heritage artwork 

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Application to Cultural Heritage artwork 

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Paintings

Metal artwork

Stone artwork

Wooden artwork

Earthware and pottery

Glass and enamel

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X-Ray source (En<60 keV)

Sample

Detector Si(Pin)

Analog signal amplifier

Multichannel analyzer MCA (analog to digital converter)

Acquisition system/data processing

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When an X-Ray beam interacts with a specimen this emits characteristic X-Rays relative to the chemical elemental content.

The analysis of the acquired spectrum permits to identify the chemical elements present in the sample. It is capable of:

Qualitative analysis: chemical elements in the sample are identified.

Quantitative/semiquantitative analysis: provides the % weight concentration of the chemical elements present in the sample.

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When a beam strikes the matter, different types of interaction can occur, depending on incident beam energy, the matrix composition of the scattering substance and the incident particle type.
In case of photons, X-Ray constituents, the interacting processes that take place are absorption and coherent/incoherent scattering.

Absorption

The interactions that characterize absorption are: the photoelectric effect (interaction with the atom's electrons), pair creation (interaction with the electric fields of the surrounding charges), photonuclear reactions (interaction with nuclei), meson photo-production (interaction with mesons).

Scattering

The interactions that occur when X and gamma rays, with energies up to some MeV, strike a substance are:

coherent scattering from a free electron (Thomson)

coherent scattering from atomic electrons (Rayleigh)

incoherent scattering from atoms (Compton)

Compared to charged particles, photons are more penetrating (the interaction with matter is less probable). They might be removed from the primary beam, causing a decrease in beam intensity but not in beam energy.

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Polycapillary optics: it is a beam focusing facility. Numerous (poly) hallow channels (capillars) are bent in such a way to capture and focalize X-Rays down to 50 micron spot.

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http://w3.lnf.infn.it/

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-special photographic techniques
-IR (infrared) reflectography
-radiography
-tomography
-gammagraphy
-holography
-ultrasound waveform analysis

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It is a NON DESTRUCTIVE (ND) technique that uses X-Ray (XR) beams with energies up to 60 keV.

The sample needs not to be treated or prepared and the analysis does not alter it.

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XRF is a diagnostic technique widely used to perform elemental analysis (Z>13) present in a sample.