Desenvolvimento de espectroscopia de plasma induzido por laser para aplicações em análise de patrimônio cultural: estudo de moedas de Um Cruzeiro de 1945 e Mil Réis de 1939 / DEVELOPMENT OF LASER INDUCED BREAKDOWN SPECTROSCOPY OF ONE

Marcello Magri Amaral

In this work, the technique of laser induced breakdown spectroscopy was developed for application in cultural heritage analysis in order to study coins of one \Cruzeiro" from 1945 and a thousand \R¶eis" from 1939, using a Nd:YAG laser operating in Q-switched mode. It had been determined the best conditions of laser and detection features such as pulse energy, delay time between the pulse and the acquisition of spectra and integration time of the spectroscopic signal for the technique applied to cultural heritage. The electronic excitation temperature, the ionization temperature and the electronic density of the plasma had been determined in order to assure the technique reproductivity. The actual damage to the coins was evaluated using the technique of Optical Coherence Tomography. Using the calibration free method, elemental composition had been determined, however the concentration for Aluminum, forge material element , was below of its nominal value and the Neutron Activation Analysis value. An investigation of the ionization fraction disclosed that the ionization fraction of present ionization in the plasma was above of the expected value for thermal ionization at measured temperatures, indicating the presence of non thermal ionization processes, in°uencing the values for Aluminum concentration. A correction in the ionic concentration of the element was performed using the ionization fraction for non thermal processes and the new concentration values had an agreement with the nominal values and the ones determined by Neutron Activation Analysis. i

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