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Uvod: Število ekspozicij dolgoročno vpliva na zmanjšanje senzibilnosti fluorescentne slikovne plošče za računalniško radiografijo, saj več ekspozicij, pomeni večjo izpostavljenost sevanju. Z merjenjem ekspozicijskega indeksa in produkta med dozo in površino ugotavljamo, koliko ionizirajočega sevanja je doseglo slikovni sprejemnik in pacienta. Če želimo ohraniti primerljiv ekspozicijski indeks med novimi in starimi slikovnimi sprejemniki, moramo ustrezno prilagoditi ekspozicijske pogoje. Namen: Namen diplomskega dela je ugotoviti, kako število ekspozicij dolgoročno vpliva na slikovne fluorescentne plošče za računalniško radiografijo ter med seboj primerjati stare in nove slikovne sprejemnike dveh različnih velikosti pri slikanju medenice. Metode dela: Za izdelavo diplomskega dela smo uporabili deskriptivno metodo pregleda literature in eksperimentalno metodo. Ta je zajemala meritve, s pomočjo katerih smo primerjali stare in nove slikovne sprejemnike ter merili kakšen vpliv ima to na dozo in ekspozicijski indeks. Pridobili smo faktorje spremembe ekspozicijskih pogojev za ohranitev približno enakega ekspozicijskega indeksa med starimi in novimi slikovnimi sprejemniki. Rezultati: V raziskavi smo ugotovili, da je ekspozicijski indeks pri uporabi novih slikovnih sprejemnikov občutno višji, zato moramo ustrezno prilagoditi ekspozicijske pogoje. V kolikor uporabimo na novih slikovnih sprejemnikih ustrezno prilagojene ekspozicijske pogoje, primerljive s starimi slikovnimi sprejemniki, dosežemo občutno zmanjšanje doze za pacienta. Razprava in zaključek: Iz rezultatov je razvidno, da obstajajo med starimi in novimi slikovnimi sprejemniki statistično značilne razlike v dozni obremenjenosti slikovnega sprejemnika in pacienta. Ravno tako ugotovimo, da število opravljenih ekspozicij tekom uporabe močno vpliva na kvaliteto slik. Introduction: The number of exposures performed on an imaging plate has a long term impact on the plate itself and lowers its sensitivity. By measuring the exposure index and the dose area product we can define how much ionizing radiation reaches the imaging plate and the patient. If we want to keep the exposure index between the old and the new plates comparable, we have to adjust the exposure parameters correctly. Purpose: The purpose of the diploma work is to assess how the number of exposures affects imaging plates for computed radiography by comparing old and new imaging plates. Methods: To write the diploma work we used the descriptive method by overviewing relevant literature, and the experimental method. This included gathering measurements, which we used to compare the old and the new imaging plates and define what impact this has on the radiation dose for the imaging plate and the dose for the patient. We adjusted the parameters to keep the exposure index comparable. Results: The research showed that the exposure index is much higher when we use a new imaging plate. That is why we have to adjust the exposure parameters. When the parameters used on the new imaging plates are comparable to the parameters used on the old imaging plates, the patient radiation dose is much lower on the new imaging plates. Discussion and conclusion: The results evidently show statistically defined differences in doses on the plate and for the patient comparing old and new imaging plates. Moreover, we can see that the number of exposures performed on an imaging plate in the time of use, affects the quality of the images.

Uvod: Število ekspozicij dolgoročno vpliva na zmanjšanje senzibilnosti fluorescentne slikovne plošče za računalniško radiografijo, saj več ekspoziciji, pomeni večjo izpostavljenost sevanju. Z merjenjem ekspozicijskega indeksa in produkta med dozo in površino ugotavljamo koliko ionizirajočega sevanja je doseglo slikovni sprejemnik in pacienta. Če želimo ohraniti primerljiv ekspozicijski indeks med novimi in starimi slikovnimi sprejemniki, moramo ustrezno prilagoditi ekspozicijske pogoje. Namen: Namen diplomskega dela je ugotoviti, kako število ekspozicij dolgoročno vpliva na slikovne fluorescentne plošče za računalniško radiografijo ter med seboj primerjati stare in nove slikovne sprejemnike pri slikanju roke in kolka. Metode dela: Za izdelavo diplomskega dela smo uporabili deskriptivno metodo pregleda literature in eksperimentalno metodo. Ta je zajemala meritve, s pomočjo katerih smo primerjali stare in nove slikovne sprejemnike ter merili kakšen vpliv ima to na dozo in ekspozicijski indeks. Pridobili smo faktorje spremembe ekspozicijskih pogojev za ohranitev približno enakega ekspozicijskega indeksa med starimi in novimi slikovnimi sprejemniki pri slikanju roke in kolka. Rezultati: V raziskavi smo ugotovili, da je ekspozicijski indeks pri uporabi novih slikovnih sprejemnikov občutno višji, zato moramo ustrezno prilagoditi ekspozicijske pogoje. V kolikor uporabimo na novih slikovnih sprejemnikih ustrezno prilagojene ekspozicijske pogoje, primerljive s starimi slikovnimi sprejemniki, dosežemo občutno zmanjšanje doze za pacienta. Razprava in zaključek: Iz rezultatov je razvidno, da obstajajo med starimi in novimi slikovnimi sprejemniki statistično značilne razlike v dozni obremenjenosti slikovnega sprejemnika in pacienta. Ravno tako ugotovimo, da število opravljenih ekspozicij tekom uporabe vpliva na kvaliteto slik. Introduction: The number of exposures performed on an imaging plate has a long term impact the plate itself and lowers its sensitivity. By measuring the exposure index and the dose area product we can define how much ionizing radiation reaches the imaging plate and the patient. If we want to keep the exposure index between the old and the new plates comparable, we have to adjust the exposure parameters correctly. Purpose: The purpose of the diploma work is to assess how the number of exposures affects imaging plates for computed radiography done on hand and hip by comparing old and new imaging plates. Methods: To write the diploma work we used the descriptive method by overviewing relevant literature, and the experimental method. This included gathering measurements, which we used to compare the old and the new imaging plates and define what impact this has on the radiation dose for the imaging plate and the dose for the patient. The radiographies were done for the hand and the hip. We adjusted the parameters to keep the exposure index comparable. Results: The research showed that the exposure index is much higher when we use a new imaging plate. That is why we have to adjust the exposure parameters. When the parameters used on the new imaging plates are comparable to the parameters used on the old imaging plates, the patient radiation dose is much lower on the new imaging plates. Discussion and conclusion: The results evidently show statistically defined differences in doses on the plate and for the patient comparing old and new imaging plates. Moreover, we can find out that the number of exposure performed on an imaging plate in the time of use, affects the quality of the images.

As an image recording medium for transmission positron microscopes, imaging plates are quite useful and powerful. Imaging plates are also quite sensitive and the photon-stimulated luminescence (PSL) is linearly proportional to the positron intensity in six digits (106). No bulky or expensive equipment is necessary to accommodate in vacuum. Imaging plates can be set under bright lights, this is different from the photographic films. Darkness is only required during exposure and transfer to a reader. Slow Positron Facility at KEK, Japan was used to study the effect of “mono-chromatic” positron beam. Specimens were set just in front of an imaging plate. After a certain time of exposure, the imaging plates were processed by a reader. Used imaging plates can be used repeatedly after erased by ultra-violet lights. Images through samples can be obtained. Similar experiments using non-monochromatic (white) positrons and electrons have been performed at Teikyo University of Science and Technology (TUST) and Research Reactor Institute, Kyoto Univ. (RRI). Sealed 22Na positron source can be conveniently used for non-destructive tests.

This work takes place in the framework of the characterization and theoptimization of laser-driven electron and photon sources. With the goal of usingthese sources for nuclear physics experiments, we focused on 2 energy ranges:one around a few MeV and the other around a few tens of keV. The first partof this work is thus dedicated to the study of detectors routinely used forthe characterization of laser-driven particle sources: Imaging Plates. A modelhas been developed and is fitted to experimental data. Response functions toelectrons, photons, protons and alpha particles are established for SR, MS andTR Fuji Imaging Plates for energies ranging from a few keV to several MeV. Thesecond part of this work present a study of ultrashort and intense electron andphoton sources produced in the interaction of a laser with a solid or liquid target.An experiment was conducted at the ELFIE facility at LULI where beams ofelectrons and photons were accelerated up to several MeV. Energy and angulardistributions of the electron and photons beams were characterized. The sourceswere optimized by varying the spatial extension of the plasma at both the frontand the back end of the initial target position. In the optimal configuration ofthe laser-plasma coupling, more than 10exponent11 electrons were accelerated. In the caseof liquid target, a photon source was produced at a high repetition rate on anenergy range of tens of keV by the interaction of the AURORE Laser at CELIA(10exponent16 W cm exponent-2) and a melted gallium target. It was shown that both the meanenergy and the photon number can be increased by creating gallium jets at thesurface of the liquid target with a pre-pulse. A physical interpretation supportedby numerical simulations is proposed., Ce travail de thèse expérimental traite de la caractérisation et de l'optimisation de sources d'électrons et de photons (gamme en énergie keV- MeV) produites lors de l'interaction d'un laser à impulsion courte et intense avec une cible à l'état de plasma. La caractérisation en énergie et angulaire de ces sources est un enjeu d'importance, notamment dans la perspective de les utiliser pour des expériences de physiques nucléaires dans les plasmas. Une partie de ce travail est consacrée à l'étude des écrans photostimulables (IPs), détecteurs couramment utilisés pour la mesure des distributions en énergie et angulaire des faisceaux de particules accélérées par laser. Les caractéristiques des écrans de type MS, SR et TR de la marque Fuji ont été étudiés et leurs fonctions de réponse aux électrons, photons, protons et particules alpha sont établies dans une gamme en énergie de quelques kev à plusieurs MeV. Enfin un protocole est proposé pour réaliser des mesures quantitatives avec ces détecteurs dans différentes configurations expérimentales.Dans une seconde partie, une source d'électrons produite avec l'installation ELFIE du LULI dans la gamme en énergie de l'ordre du MeV a été caractérisée et optimisée en faisant varier l’extension spatiale du pré-plasma dans lequel interagi le laser intense. En particulier nous montrons que plus de 1011 électrons de plus de 10 MeV sont accélérés lors de l’interaction laser- plasma pour des conditions particulières d’extension longitudinale du pré-plasma en amont, mais aussi en aval de la cible.Dans une dernière partie, une source de photons produite à haute cadence avec le laser AURORE du CELIA est étudiée dans une gamme en énergie d'une dizaine de keV. L’originalité de la source réside dans la nature de la cible qui est du gallium à l'état liquide. Nous montrons en particulier que l'énergie moyenne et le nombre des photons peuvent être optimisés en créant des jets de gallium à la surface de la cible au moyen d'une pré-impulsion laser. Une interprétation physique du phénomène est proposée s’appuyant sur des simulations numériques.