Estados Nucleares isoméricos são estados que decaem com vidas-médias longas ( T1/2 > 10 ns) e revelam, em geral, uma grande mudança no momento angular no seu decaimento, um pequeno elemento de matriz ou uma baixa energia de transição. Através da medida da vida-média de estados nucleares é possível obter informações sobre a função de onda desse estado, representando um teste rigoroso para modelos nucleares. Neste trabalho foi utilizado um sistema desenvolvido no Laboratório Aberto de Física Nuclear (LAFN) da Universidade de São Paulo chamado SIStema para Medida de Estados Isoméricos (SISMEI), que utiliza coincidência atrasada entre partículas evaporadas numa reação nuclear e raios gama emitidos pelo estado isomérico. O SISMEI consiste de cintiladores plásticos para detecção das partículas, detectores de germânio hiperpuro (HPGe) e iodeto de sódio (NaI(Tl)) para raios gama, associados a uma eletrônica de coincidência, instalado no acelerador Pelletron (8UD) do LAFN. Neste trabalho, realizou-se um experimento para medir o estado isomérico 7(-) (E = 1229,87(4) keV) do 68Ga. A tomada de dados durou cerca de 80 horas com uma taxa de eventos de aproximadamente 80000 contagens por hora. O resultado obtido foi T 1/2 = 60, 8(11) ns, que é compatível com os resultados experimentais de outros trabalhos, porém, mais preciso. A estrutura desse núcleo foi calculada através do Modelo de Camadas em Larga Escala considerando-se duas interações residuais diferentes FPG e JUN45; os resultados foram comparados entre si, juntamente com os valores obtidos em outros trabalhos. Os cálculos realizados com o Modelo de Camadas reproduziram relativamente bem a energia e a ordem dos estados excitados do 68Ga, a interação FPG conseguiu descrever melhor a probabilidade de transição quadrupolar elétrica B(E2) diretamente ligada à vida-média do estado. / Isomeric nuclear states are nuclear states which decay with long lifetimes (T1/2 > 10 ns); their study generally reveals, a large change in angular momentum in its decay, a small matrix element or a small transition energy. By measuring lifetimes of isomeric states it is possible to obtain information about this states wave function, being a robust test for nuclear models. In this work, a system developed at the Laboratório Aberto de Fsica Nuclear (LAFN) of University of São Paulo called System for the Measurement of Isomeric States (SISMEI) was utilized. Delayed coincidence between evaporated particles in a nuclear reaction and the delayed gamma-rays emitted from the isomeric state was used to measure lifetimes. SISMEI is composed of plastic scintillators for particle detection, hiperpure germanium detectors (HPGe) and sodium iodide (NaI(Tl)) for gamma-ray detection, coupled to a coincidence system, located on 30A beam line of the Pelletron (8UD) accelerator - LAFN. In the present work, an experiment to measure the 7 (-) (E = 1229.87(4) keV) isomeric state of 68Ga was performed. The experiment took about 80 hours with an event rate of about 80000 counts per second. The measured value was T 1/2 = 60.8(11) ns, which is compatible, but more accurate, with experimental results of other authors. The nuclear structure of this nucleus was calculated with the Large Scale Shell Model by using two different residual interactions FPG and JUN45; the results were compared with the known values. The structure calculated with LSSM described the energy states and the order of excited states relatively well; the FPG interaction was capable to describe better the quadrupolar electrical transition probability B(E2), which is direct related to predicting the state lifetime.

Estados Nucleares isoméricos são estados que decaem com vidas-médias longas ( T1/2 > 10 ns) e revelam, em geral, uma grande mudança no momento angular no seu decaimento, um pequeno elemento de matriz ou uma baixa energia de transição. Através da medida da vida-média de estados nucleares é possível obter informações sobre a função de onda desse estado, representando um teste rigoroso para modelos nucleares. Neste trabalho foi utilizado um sistema desenvolvido no Laboratório Aberto de Física Nuclear (LAFN) da Universidade de São Paulo chamado SIStema para Medida de Estados Isoméricos (SISMEI), que utiliza coincidência atrasada entre partículas evaporadas numa reação nuclear e raios gama emitidos pelo estado isomérico. O SISMEI consiste de cintiladores plásticos para detecção das partículas, detectores de germânio hiperpuro (HPGe) e iodeto de sódio (NaI(Tl)) para raios gama, associados a uma eletrônica de coincidência, instalado no acelerador Pelletron (8UD) do LAFN. Neste trabalho, realizou-se um experimento para medir o estado isomérico 7(-) (E = 1229,87(4) keV) do 68Ga. A tomada de dados durou cerca de 80 horas com uma taxa de eventos de aproximadamente 80000 contagens por hora. O resultado obtido foi T 1/2 = 60, 8(11) ns, que é compatível com os resultados experimentais de outros trabalhos, porém, mais preciso. A estrutura desse núcleo foi calculada através do Modelo de Camadas em Larga Escala considerando-se duas interações residuais diferentes FPG e JUN45; os resultados foram comparados entre si, juntamente com os valores obtidos em outros trabalhos. Os cálculos realizados com o Modelo de Camadas reproduziram relativamente bem a energia e a ordem dos estados excitados do 68Ga, a interação FPG conseguiu descrever melhor a probabilidade de transição quadrupolar elétrica B(E2) diretamente ligada à vida-média do estado. / Isomeric nuclear states are nuclear states which decay with long lifetimes (T1/2 > 10 ns); their study generally reveals, a large change in angular momentum in its decay, a small matrix element or a small transition energy. By measuring lifetimes of isomeric states it is possible to obtain information about this states wave function, being a robust test for nuclear models. In this work, a system developed at the Laboratório Aberto de Fsica Nuclear (LAFN) of University of São Paulo called System for the Measurement of Isomeric States (SISMEI) was utilized. Delayed coincidence between evaporated particles in a nuclear reaction and the delayed gamma-rays emitted from the isomeric state was used to measure lifetimes. SISMEI is composed of plastic scintillators for particle detection, hiperpure germanium detectors (HPGe) and sodium iodide (NaI(Tl)) for gamma-ray detection, coupled to a coincidence system, located on 30A beam line of the Pelletron (8UD) accelerator - LAFN. In the present work, an experiment to measure the 7 (-) (E = 1229.87(4) keV) isomeric state of 68Ga was performed. The experiment took about 80 hours with an event rate of about 80000 counts per second. The measured value was T 1/2 = 60.8(11) ns, which is compatible, but more accurate, with experimental results of other authors. The nuclear structure of this nucleus was calculated with the Large Scale Shell Model by using two different residual interactions FPG and JUN45; the results were compared with the known values. The structure calculated with LSSM described the energy states and the order of excited states relatively well; the FPG interaction was capable to describe better the quadrupolar electrical transition probability B(E2), which is direct related to predicting the state lifetime.

No description available.

<p>Испитана је тачност методе мерења<br />апсолутне активности гама емитера помоћу једног<br />гама спектрометра на већим брзинама бројања. У<br />оквиру истраживања нађен је једноставан<br />поступак за корекцију спектралних података на<br />случајне коинциденције.<br />&nbsp;&nbsp; Принцип коинцидентне технике и корекције<br />сумарног врха и врхова пуне енергије помоћу<br />врхова у спектру насталим само услед случајних<br />коинциденција примењен је на радиоизотопе са<br />једноставном и веома сложеном шемом. Изведене<br />су једноставне формуле за мерења активности са и<br />без корекције на ефективне угаоне корелације у<br />којима фигуришу подаци само из једног гама<br />спектра чиме је постигнута знатна једноставност у<br />техници мерења.<br />&nbsp;&nbsp; Резултати овог истраживања показали су да<br />се активност двофотонских гама емитера може<br />измерити помоћу HPGe детектора и дигиталне<br />спектроскопске јединице са тачношћу испод 1% на<br />разним брзинама бројања само помоћу једног<br />спектра. Резултати за изотопе са сложеном шемом<br />добијени једноставном техником указују да се<br />техника може применити на рутинска мерења где<br />грешка не превазилази 10%</p> / <p>Ispitana je tačnost metode merenja<br />apsolutne aktivnosti gama emitera pomoću jednog<br />gama spektrometra na većim brzinama brojanja. U<br />okviru istraživanja nađen je jednostavan<br />postupak za korekciju spektralnih podataka na<br />slučajne koincidencije.<br />&nbsp;&nbsp; Princip koincidentne tehnike i korekcije<br />sumarnog vrha i vrhova pune energije pomoću<br />vrhova u spektru nastalim samo usled slučajnih<br />koincidencija primenjen je na radioizotope sa<br />jednostavnom i veoma složenom šemom. Izvedene<br />su jednostavne formule za merenja aktivnosti sa i<br />bez korekcije na efektivne ugaone korelacije u<br />kojima figurišu podaci samo iz jednog gama<br />spektra čime je postignuta znatna jednostavnost u<br />tehnici merenja.<br />&nbsp;&nbsp; Rezultati ovog istraživanja pokazali su da<br />se aktivnost dvofotonskih gama emitera može<br />izmeriti pomoću HPGe detektora i digitalne<br />spektroskopske jedinice sa tačnošću ispod 1% na<br />raznim brzinama brojanja samo pomoću jednog<br />spektra. Rezultati za izotope sa složenom šemom<br />dobijeni jednostavnom tehnikom ukazuju da se<br />tehnika može primeniti na rutinska merenja gde<br />greška ne prevazilazi 10%</p> / <p>It has been investigated the accuracy of absolute<br />activity measurement of gamma emitters with a single<br />gamma spectrometer at higher count rates. In this<br />research it has been found relatively simple procedure<br />for random summing correction of spectral data.<br />Principle of coincidence technique and random<br />summing correction of sum peaks and full energy<br />peaks using pile up peaks is applied to measure<br />absolute activity of simple and complicated decay<br />scheme radioisotopes. Simple equations were deduced<br />for absolute activity measurements with and without<br />correction for effective angular correlations. Variables<br />in these equations are spectral data only. Great<br />simplicity is achieved in coincidence technique of<br />absolute activity measurement.<br />It was shown that absolute activity of<br />radioisotopes emitting simultaneously two gamma<br />photons can be measured with accuracy below 1% at<br />high count rates using HPGe detector and DSP<br />spectroscopy unit. Measurements of complicated<br />decay scheme radioisotopes shown that simple<br />technique is able to bring satisfactory results with<br />accuracies below 10%</p>

Cette thèse est consacrée au problème de la comparaison de deux partitions non strictes (floues/probabilistes, possibilistes) d’un même ensemble d’individus en plusieurs clusters. Sa résolution repose sur la définition formelle de mesures de concordance reprenant les principes des mesures historiques développées pour la comparaison de partitions strictes et trouve son application dans des domaines variés tels que la biologie, le traitement d’images, la classification automatique. Selon qu’elles s’attachent à observer les relations entre les individus décrites par chacune des partitions ou à quantifier les similitudes entre les clusters qui composent ces partitions, nous distinguons deux grandes familles de mesures pour lesquelles la notion même d’accord entre partitions diffère, et proposons d’en caractériser les représentants selon un même ensemble de propriétés formelles et informelles. De ce point de vue, les mesures sont aussi qualifiées selon la nature des partitions comparées. Une étude des multiples constructions sur lesquelles reposent les mesures de la littérature vient compléter notre taxonomie. Nous proposons trois nouvelles mesures de comparaison non strictes tirant profit de l’état de l’art. La première est une extension d’une approche stricte tandis que les deux autres reposent sur des approches dite natives, l’une orientée individus, l’autre orientée clusters, spécifiquement conçues pour la comparaison de partitions non strictes. Nos propositions sont comparées à celles de la littérature selon un plan d’expérience choisi pour couvrir les divers aspects de la problématique. Les résultats présentés montrent l’intérêt des propositions pour le thème de recherche qu’est la comparaison de partitions. Enfin, nous ouvrons de nouvelles perspectives en proposant les prémisses d’un cadre qui unifie les principales mesures non strictes orientées individus. / This thesis is dedicated to the problem of comparing two soft (fuzzy/ probabilistic, possibilistic) partitions of a same set of individuals into several clusters. Its solution stands on the formal definition of concordance measures based on the principles of historical measures developped for comparing strict partitions and can be used invarious fields such as biology, image processing and clustering. Depending on whether they focus on the observation of the relations between the individuals described by each partition or on the quantization of the similarities between the clusters composing those partitions, we distinguish two main families for which the very notion of concordance between partitions differs, and we propose to characterize their representatives according to a same set of formal and informal properties. From that point of view, the measures are also qualified according to the nature of the compared partitions. A study of the multiple constructions on which the measures of the literature lie completes our taxonomy. We propose three new soft comparison measures taking benefits of the state of art. The first one is an extension of a strict approach, while the two others lie on native approaches, one individual-wise oriented, the other cluster-wise, both specifically defined to compare soft partitions. Our propositions are compared to the existing measures of the literature according to a set of experimentations chosen to cover the various issues of the problem. The given results clearly show how relevant our measures are. Finally we open new perspectives by proposing the premises of a new framework unifying most of the individual-wise oriented measures.

In this thesis, multiple ionisation processes of free atoms and molecules upon single photon absorption are studied by means of a versatile multi-electron-ion coincidence spectroscopy method based on a magnetic bottle, primarily in combination with synchrotron radiation. The latter offered the possibility to access not only valence but also core levels, revealing processes, which promote the target systems into different charge states. One study focuses on double and triple ionisation processes of acetaldehyde (ethanal) in the valence region as well as single and double Auger decay of initial 1s core vacancies. The latter are investigated site-selectively for the two chemically different carbon atoms of acetaldehyde, scrutinising theoretical predictions specifically made for that system. A related study concentrates on core-valence double ionisation spectra of acetaldehyde, which have been investigated in the light of a previously established empirical model, and which have been used as test cases for analysing this kind of spectra by means of quantum chemical electronic structure methods of increasing sophistication. A third study investigates site-specific fragmentation upon 1s photoionisation of acetaldehyde using a magnetic bottle augmented with an in-line ion time-of-flight mass spectrometer. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. A site-specificity parameter P∆ is introduced to show that differences in fragmentation behavior between initial ionisations at chemically different carbon atoms probably persist even for identical internal energy contents in the nascent dications. In another study where both electrons and ions from Auger decay of core-excited and core-ionised states of CO2 are detected in coincidence, it is confirmed that O2+ is formed specifically in Auger decay from the C1s → π* and O1s → π* resonances, suggesting a decisive role of the π* orbital in the molecular rearrangement. Also, the molecular rearrangement is found to occur by bending in the resonant states, and O2+ is produced by both single and double Auger decay. A new version of the multi-electron-ion coincidence method, where the ion time-of-flight spectrometer is mounted perpendicularly to the electron flight tube, which affects less the electron resolution and which allows for position sensitive detection of the ions, is employed in combination with tunable soft X-rays to reveal the branching ratios to final Xen+ states with 2 &lt; n &lt; 9 from pure 4d-1, 4p-1, 4s-1, 3d-1 and 3p-1 Xe+ hole states. The coincident electron spectra give information on the Auger cascade pathways. / <p>Byte av lokal vid disputation till Polhemssalen.</p>

>Magister Scientiae - MSc / An increasing number of measurements reveal the presence of a low-energy enhancement in the gamma-ray strength function (GSF). The GSF, which is the ability of nuclei to absorb or emit rays, provides insight into the statistical properties of atomic nuclei. For this project the GSF was studied for 74Ge which was populated in the reaction 74Ge(p,p')74Ge* at a beam energy of 18 MeV. The data were collected with the STARS-LIBERACE array at Lawrence Berkeley National Laboratory. Silicon detector telescopes were used for particle identi cation and rays in coincidence were detected with 5 clover-type high-purity germanium detectors. Through the analysis particle- - coincidence events were constructed. These events, together with well-known energy levels, were used to identify primary rays from the quasicontinuum. Primary rays from a broad excitation energy region, which decay to six 2+ states could be identi ed. These states and the associated primary rays are used to measure the GSF for 74Ge with the Ratio Method [1], which entails taking ratios of e ciency-corrected primary -ray intensities from the quasicontinuum. Results from the analysis of the data and focus on the existence of the low-energy enhancement in 74Ge will be discussed. The results are further discussed in the context of other work done on 74Ge using the ( , ') [2], (3He,3He') [3] and ( , ') [4] reactions.

Amostras de nitrato de potássio e enxofre natural foram irradiadas no núcleo do reator de pesquisas IEA-R1 do Instituto de Pesquisas Energéticas e Nucleares, IPEN/CNEN-SP, operando entre 3,5 e 5 MW de potência, para determinar as secções de choque térmicas e integrais de ressonância das reações 34S(n,)35S e 42K(n,)43K. O fluxo de nêutrons foi monitorado com ligas ouro-alumínio. As atividades induzidas nos alvos de ouro-alumínio e nitrato de potássio foram medidas com um detector semicondutor de germânio hiper puro; as atividades dos alvos de enxofre foram determinadas com um sistema de coincidências 4\\pi\\beta - \\gamma. Os efeitos de depressão de fluxo, autoblindagem e autoabsorção nos alvos foram corrigidos com base em simulações com o método de Monte Carlo por meio do programa MCNP. O programa PENELOPE, também baseado no método de Monte Carlo, foi modificado para simular o comportamento do sistema de coincidências 4\\pi\\beta - \\gamma. O formalismo de Westcott e o método da razão de cádmio foram usados para determinar os fluxos de nêutrons térmicos e epitérmicos, assim como as secções de choque térmicas e integrais de ressonância de ambos nuclídeos. Foi efetuado um tratamento estatístico das incertezas envolvidas e determinadas as covariâncias entre os resultados, incluindo aquelas decorrentes das incertezas do padrão de referência (ouro). As reações 34S(n,)35S e 42K(n,)43K apresentaram, respectivamente, seções de choque térmicas de 228(14) mb e 44,8(9) b, e integrais de ressonância de 144(6) mb e 1635(75) b. Estes resultados são incompatíveis com aqueles obtidos com cálculos teóricos. A seção de choque térmica da reação 34S(n,)35S concorda com valores obtidos por outros autores, dentro das incertezas experimentais. / Samples of potassium nitrate and natural sulphur were irradiated in the IPEN/CNEN-SP IEA-R1 research reactor core, operating between 3.5 and 5 MW, to determine the thermal neutron cross sections and resonance integrals of 34S(n,)35S and 42K(n,)43K reactions. The neutron flux was monitored with gold-aluminium alloy. The activities induced in targets of gold-aluminium and potassium nitrate were measured with a high purity germanium detector. Sulphur targets activities were determined with a 4\\pi\\beta-\\gamma coincidences system by the tracer method. Flux depression, self-shielding and self-absorption in the targets was evaluated by simulations using the MCNP software. The PENELOPE software, also based on Monte Carlo method, was modified to simulate the behavior of the 4\\pi\\beta-\\gamma coincidence system. The Westcott formalism and the cadmium ratio method were used to determine epithermal and thermal neutrons flux as well as the thermal cross sections and resonance integrals of both nuclides. A statistical analysis of the uncertainties was performed and the covariance between the results was determined, including those arising from the uncertainties of the gold reference standard. The results were compared with experimental values and theoretical predictions obtained by other authors. The 34S(n,)35S and 42K(n,)43K reactions had, respectively, thermal cross sections of 228(14) mb and 44.8(9) b, and integral resonances of 144(6) mb and 1635(75) b. These results are incompatible with the obtained with theoretical calculations. The 34S(n,)35S reaction thermal cross section agrees with values obtained by other authors, within the experimental uncertainties.

O Laboratório de Metrologia Nuclear (LMN) do Instituto de Pesquisas Energéticas e Nucleares (IPEN) realizou a padronização primária dos radionuclídeos 64Cu e 166Ho. Esses radioisótopos são utilizados na Medicina Nuclear em investigações diagnósticas e em radioterapia. A atividade absoluta foi determinada utilizando o método de coincidências 4&pi;&beta;(PC)- &gamma; associado à técnica de extrapolação de eficiência. Para isto, foram utilizados um contador proporcional em geometria 4&pi; acoplado ao um contador de cintilação NaI (Tl). Para a padronização do 64Cu foram utilizados dois sistemas para registro de dados: sistema TAC e sistema SCS. No sistema TAC é utilizado o módulo Time to Amplitude Converter (TAC) associado a um analisador multicanal, sendo que a eficiência do detector 4&pi;PC foi variada por meio de absorvedores externos e foi aplicado fator de correção para as eficiências beta denominado fator Kawada. No sistema SCS (Software Coincidence System) o registro dos eventos foi feito por meio da digitalização dos pulsos, a eficiência do detector 4&pi;PC foi variada por discriminação eletrônica e a atividade foi obtida pela extrapolação biparamétrica. A padronização do 166Ho em sistema de coincidências 4&pi;&beta;(PC)- &gamma; foi realizada utilizando o sistema de aquisição de dados por software, SCS (Software Coincidence System). Para determinação das probabilidade de emissão gama dos radionuclídeos foi utilizado um espectrômetro gama HPGe calibrado com ampolas padrão de 152Eu, 60Co, 133Ba, 137Cs e 241Am, calibradas no sistema primário 4&pi;&beta;(PC)- &gamma;. A probabilidade de emissão gama por decaimento do fóton de 1345,7 keV do 64Cu obtida foi de 0,472 (10) % apresentando um bom acordo com os dados da literatura. A probabilidade de emissão gama por decaimento do fóton gama de 1379,45 keV do 166Ho foi de 0,936 (4) %. Por meio destas medidas foi possível também a determinação das intensidades relativas de outros fótons emitidos por este radionuclídeo. Os resultados obtidos foram concordantes com a literatura dentro da incerteza experimental. / The procedure followed by the Nuclear Metrology Laboratory (LMN) at the Nuclear and Energy Research Institute (IPEN) for the primary standardization of 64Cu and 166Ho is described. These radionuclides are widely applied to Nuclear Medicine such as in diagnostic investigations and in radiotherapy. The absolute activity of both radionuclides were determined by the efficiency extrapolation method applied to 4&pi;&beta;(PC)-&gamma; coincidence counting system using a proportional counter in 4&pi; geometry coupled with NaI(Tl) scintillation counter. The primary standardisation of 64Cu for the conventional coincidence counting, the events were registered using a Time to Amplitude Converter (TAC) system associated with a multi-channel analyzer and by a software coincidence counting system, SCS, a digital method for primary activity measurements that simplifies the setting of optimal coincidence parameters. For perfoming the standardization of 64Cu in the TAC system, the efficiency of the 4&pi;&beta;(PC)-&gamma; detector was varied using external absorbers and in order to correct the beta efficiency, the Kawada factor was applied. In the SCS counting, the events were registered by means of pulse digitalization and the efficiencies (&epsilon;EC and &epsilon;&beta;) were varied through eletronic discrimination. The biparametric method was used for determining the absolute activity and the result was in good agreement with the ones obtained with TAC system. The standardization of 166Ho in the primary system was performed using the software coincidence counting, SCS. The gamma-ray emission probability per decay of the main transitions of both radionuclides were determined using the results obtained from the primary method, the 4&pi;&beta;(PC)-&gamma; coincidence system, associated with a calibrated HPGe gamma-ray spectrometer with standard ampoules of 152Eu, 60Co, 133Ba, 137Cs e 241Am, previously standardized in the 4&pi;&beta;(PC)-&gamma; system. The gamma-ray emission probability per decay of the 1345,7 keV transition of 64Cu was 0,472 (10) %, in good agreement with the literature. The gamma-ray emission probability per decay of the 1379,45 keV transition of 166Ho was 0,936 (4) %. It were also determined the relative gamma ray emmission probability of other gamma rays for this nuclide . All the results obtained were in good agreement with the literature.

Cette thèse est dédiée à l’étude et l’exploitation des propriétés remarquables de la distribution angulaire des photoélectrons dans le référentiel moléculaire (MFPAD pour Molecular Frame Photoelectron Angular Distribution). Cette observable sensible permet de caractériser au meilleur niveau à la fois les processus de photoionisation (PI) de petites molécules, par la détermination des modules et phases relatives des éléments de matrice dipolaire, et l’état de polarisation du rayonnement ionisant, entièrement encodé dans son expression sous la forme des paramètres de Stokes (s1, s2, s3), qui constituent les deux axes du travail présenté. La mesure des MFPADs combine une technique de spectroscopie tridimensionnelle en coïncidence des vecteurs vitesse du photoélectron et du photoion issus de la même réaction de photoionisation dissociative (PID) à l’utilisation de différentes sources de lumière : le rayonnement synchrotron d’une part, sur les lignes DESIRS et PLEIADES (SOLEIL), et le rayonnement harmonique (HHG) généré par l’interaction d’un champ laser intense sur une cible gazeuse d’autre part, sur la plateforme PLFA (SLIC, groupe Attophysique du LIDyL, CEA Saclay).La première partie de la thèse est consacrée à la caractérisation complète de l’état de polarisation d’un rayonnement incident. Pour cela, une méthode originale de « polarimétrie moléculaire » est introduite et qualifiée sur la ligne DESIRS équipée d’un polarimètre optique VUV étalon. Mise en œuvre pour déterminer complètement l’ellipse de polarisation du rayonnement HHG produit dans différentes configurations sur la source secondaire XUV PLFA, elle conduit à des résultats originaux incluant notamment la distinction entre les composantes circulaire et non polarisée du rayonnement étudié.La seconde partie porte sur la PID des molécules H2, D2 et HD induite à résonance avec les états doublement excités Q1 et Q2 par une lumière polarisée circulairement. Dans cette région énergétique (30-35 eV) où l’ionisation directe, l’autoionisation et la dissociation sont en compétition sur une échelle de quelques femtosecondes, l’excitation photonique donne lieu à une dynamique couplée électron-noyau ultrarapide. Les asymétries remarquables observées dans le dichroïsme circulaire dans le référentiel moléculaire, comparées aux calculs quantiques du groupe de F. Martín (UAM, Madrid), constituent une sonde sensible des interférences quantiques entre des chemins réactionnels indiscernables impliquant des cœurs ioniques de symétrie u/g différente. / This is thesis is dedicated to the study and the use of the remarkable properties of the molecular frame photoelectron angular distribution (MFPAD). This observable is a very sensitive probe of both the photoionization (PI) processes in small molecules, through the determination of the magnitudes and relative phases of the dipole matrix elements, and the polarization state of the ionizing light, which is entirely encoded in the MFPAD in terms of the Stokes parameters (s1, s2, s3). MFPAD measurements take advantage of dissociative photoionization (DPI) processes by combining an electron-ion 3D momentum spectroscopy technique with the use of different radiation facilities: SOLEIL synchrotron (DESIRS and PLEIADES beamlines) and the XUV PLFA beamline (SLIC, LIDyL Attophysics group, CEA Saclay) based on the interaction of a strong laser field with a gaseous target called high harmonic generation (HHG).The first part of the thesis is devoted to the complete characterization of the polarization state of an incoming radiation. In this context, an original “molecular polarimetry” method is introduced and demonstrated by comparison with a VUV optical polarimeter available on the DESIRS beamline. Using this method to determine the full polarization ellipse of HHG radiation generated in different conditions on the XUV PLFA facility leads to original results that include the challenging disentanglement of the circular and unpolarized components of the studied radiation.The second part deals with the study of DPI of the H2, D2 and HD molecules induced by circularly polarized light at resonance with the doubly excited states Q1 and Q2. In this energy region (30-35 eV) where direct ionization, autoionization and dissociation compete on a femtosecond timescale, the photonic excitation gives rise to complex ultrafast electronic and nuclear coupled dynamics. The remarkable asymmetries observed in the circular dichroism in the molecular frame, compared to quantum calculations of the group of F. Martín (UAM, Madrid), constitute a very sensitive probe of the quantum interferences between indistinguishable DPI channels involving ionic states of different u/g symmetry.