<p>U ovoj disertaciji su prikazani rezultati kompleksnih istraživanja uticaja<br />kosmičkog zračenja na nuklearne spektre na nivou mora.<br />Utvrđivanje specifičnih vremenskih intervala u vremenskom spektru,<br />kojima odgovaraju tačno određene grupe događaja indukovane<br />kosmičkim mionima, omogućava adekvatno odbacivanje ometajućih<br />događaja u željenim energetskim oblastima detektovanih spektara, pri<br />antikoincidentnom režimu rada ultraniskofonskih sistema. U prvom<br />eksperimentu prikazanom u ovoj disertaciji,&nbsp; istraživana je mogućnost<br />vremenskog razlaganja detektovanih događaja,&nbsp; pomoću koincidentnog<br />sistema u čijem sklopu se nalazi HPGe detektor i&nbsp; plastični scintilator, u<br />povr&scaron;inskoj laboratoriji. Ustanovljeno je da se promptni i zakasneli<br />koincidentni događaji između plastičnog &ldquo;veto&rdquo; detektora i<br />germanijumskog detektora mogu jasno razdvojiti u dve grupe, za oko<br />100 ns. Dodatno, zakočno zračenje i&nbsp; anihilacioni događaji mogu se<br />razdvojiti u vremenu od (n,n&rsquo;) događaja, iako svi ovi događaji pripadaju<br />grupi zakasnelih događaja. Takođe, registrovani su&nbsp; i&nbsp; značajno zakasneli<br />anihilacioni događaji, koji nastaju usled raspada zaustavljenih pozitivnih<br />miona.<br />Drugi eksperiment prikazan u ovoj disertaciji baziran je na ultra-niskofonskom HPGe spektrometru relativne efikasnosti 100%.<br />Dodatkom dva plastična scintilatora i brzo-sporog koincidentnog kola,<br />istraživani su koincidentni događaji između plastičnih scintilatora i<br />HPGe spektrometra. Ovaj spektrometarski sistem MIREDO <em>(Muon<br />Induced Rare Event Dynamic Observatory</em>) prvenstveno je namenjen<br />proučavanju procesa indukovanih kosmičkim mionima u različitim<br />materijalima. Analiza ovakvih interakcija može biti od značaja za ultra-niskofonske eksperimente. Rezultati dobijeni za tri ispitivana materijala,<br />pakovana u<em> Marinelli</em> sud, prezentovani su i diskutovani.<br />U trećem eksperimentu prikazanom u ovoj disertaciji ispitan je<br />potencijalni uticaj solarnih&nbsp; neutrina&nbsp; na izmerenu brzinu&nbsp; radioaktivnog<br />raspada,&nbsp; merenjem varijacija u brzini brojanja<br />³H&nbsp; metodom tečnog&nbsp;scintilacionog brojanja. Kori&scaron;ćenjem sofisticiranog tečnog scintilacionog&nbsp;spektrometra&nbsp;<em> Quantulus</em>&nbsp; ustanovljeno je da na merenje<br />visokoenergetskog dela&nbsp;³H spektra može značajno uticati nestabilnost<br />instrumenta. Oscilatorni karakter izmerenog visokoenergetskog dela<br />³H&nbsp;spektra&nbsp; je registrovan, ali sa veoma malom amplitudom (manjom od<br />0.5%), koja se ne može jednostavno objasniti samo nestabilno&scaron;ću<br />instrumenta.&nbsp; Kada je meren ukupan&nbsp;³H spektar, nisu nađene značajne<br />varijacije u brzini brojanja.<br />Već duže vreme je poznato da je niskoenergetsko gama zračenje<br />kontinualne distribucije prisutno na otvorenom prostoru, u vazduhu na<br />povr&scaron;ini Zemlje. U prethodnim istraživanjima pretpostavljano je da&nbsp; ovo<br />zračenje potiče skoro isključivo od gama fotona koji su emitovani usled<br />prirodne radioaktivnosti i potom rasejani u nazad od strane vazduha<br />iznad zemlje. U četvrtom eksperimentu prikazanom u ovoj disertaciji<br />pokazano je da&nbsp; je&nbsp; ovo zračenje (u energetskom regionu 30 keV-300<br />keV), sa maksimumom na oko&nbsp; 90 keV, u značajnoj meri&nbsp; proizvedeno<br />kosmičkim zračenjem, sa fluksom fotona od oko 3000 m^-2s^-1. Takođe,<br />ustanovljeno je da dozama op&scaron;te populacije doprinosi ovo sveprisutno<br />niskoenergetsko gama zračenja kosmičkog porekla, zajedno sa<br />odgovarajućim fluksom niskoenergetskih elektrona i da ove komponente<br />ukupnih doza indukovanih kosmičkim zračenjem na nivou mora nisu<br />zanemarljive.</p> / <p>In this dissertation results of complex research on cosmic-ray impact on&nbsp;nuclear spectra at sea level are shown.&nbsp; The appropriate selection of&nbsp;coincidence time interval &nbsp;in low-background experiments that are based&nbsp;on the rejection of anticoincidence background events is very important&nbsp;for reducing the influence of cosmic-ray muons on acquired spectral&nbsp;data. In&nbsp; the first&nbsp; experiment&nbsp; presented in this dissertation,&nbsp; performed by&nbsp;the coincidence system of an HPGe detector and a plastic detect or&nbsp; in a&nbsp;surface laboratory, the time resolution of the detected events is explored.&nbsp;It is&nbsp; found that the prompt and delayed coincidence events between a&nbsp;plastic veto detector and a &nbsp;Ge detector can be sharply divided for&nbsp;approximately 100 ns in two groups. In addition, the bremsstrahlung&nbsp;and annihilation events can&nbsp; be time-resolved from the (n,n&rsquo;) events,&nbsp;although all of these events belong to the group of delayed events. Also,&nbsp;substantially delayed annihilation events, which are caused by the&nbsp;<br />decays of stopped positive muons, were detected.<br />The second experiment shown in this dissertation is based on the 100%&nbsp;relative efficiency ultra-low-background HPGe spectrometer. With the&nbsp;addition of two plastic scintillators and a fast-slow coincidence circuit,&nbsp;the coincidence events between the plastic detectors and the HPGe&nbsp;spectrometer have been investigated. This&nbsp; MIREDO (Muon Induced&nbsp;Rare Event Dynamic Observatory) spectrometer system is primarily&nbsp;<br />developed for the study of cosmic muon induced processes in different&nbsp;materials. Exploration of such interactions can be important for ultra-low&nbsp;background experiments. Results derived for three samples, placed in a&nbsp;Marinelli beaker, are presented and discussed.<br />In third experiment shown in this dissertation,&nbsp; the potential influence of&nbsp;solar neutrinos on measured decay rate is investigated by&nbsp; the liquid&nbsp;scintillation measurement of the count rate variations of&nbsp;³H. Making use of the sophisticated Quantulus liquid scintillation spectrometer, it is&nbsp;found that the&nbsp; measurement of the high-energy tail of&nbsp;³H spectrum may be significantly influenced by instrumental&nbsp; instability.&nbsp; The oscillatory behavior of measured high-energy tail of ³H spectrum&nbsp; is registered, but&nbsp;with very small amplitude (less than 0.5%), which cannot&nbsp; be easily&nbsp;<br />explained only by instrumental instability. When the total&nbsp;³H spectrum was measured, no significant variations in the count rate were found.&nbsp;<br />For a long time, it has been known that low-energy continuous gamma&nbsp;radiation is present in open air at the Earth&rsquo;s surface. In previous&nbsp;investigations it was assumed that this radiation is produced almost&nbsp;exclusively by gamma photons emitted due to the natural radioactivity,&nbsp;which are backscattered by air above ground.&nbsp; In the fourth experiment&nbsp;presented in this dissertation, it is&nbsp; shown&nbsp; that significant amount of this&nbsp;<br />radiation (related to energy region 30&nbsp; keV-300&nbsp; keV) that peaks at about&nbsp;90 keV, is produced by cosmic-rays, with the photon flux of about 3000&nbsp;m^-2s^-1.&nbsp; Also, it is found&nbsp; that the contribution of this omnipresent low&nbsp;energy gamma radiation of cosmic-ray origin, including the&nbsp;corresponding low-energy electron flux, to the doses of general&nbsp;<br />population are non-negligible components of overall doses induced by&nbsp;cosmic rays near sea level.</p>

Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation ou la désintégration de la MN dans le halo de la Voie Lactée. Les efforts expérimentaux actuels se focalisent principalement sur une gamme d'énergie de l'ordre du GeV au TeV, où un signal de WIMP (Weakly Interacting Massive Particles) est attendu. L'analyse des mesures récentes et inédites des rayons cosmiques chargés (antiprotons, électrons et positrons) et leurs émissions secondaires et les améliorations des modèles astrophysiques sont présentées.Les données de PAMELA sur les antiprotons contraignent l'annihilation et la désintégration de la MN de manière similaire (et même légèrement meilleurs) que les contraintes les plus fortes venant des rayons gamma, même dans le cas où les énergies cinétiques inférieures à 10 GeV sont écartées. En choisissant des paramètres astrophysiques différents (modèles de propagation et profils de MN), les contraintes peuvent changer d'un à deux ordres de grandeur. Pour exploiter la totalité de la capacité des antiprotons à contraindre la MN, des effets précédemment négligés sont incorporés et se révèlent être importants dans l'analyse des données inédites de AMS-02 : ajouter les pertes d'énergie, la diffusion dans l'espace des moments et la modulation solaire peut modifier les contraintes, même à de hautes masses. Une mauvaise interprétation des données peut survenir si ces effets ne sont pas pris en compte. Avec les flux de protons et d'hélium exposé par AMS-02, le fond astrophysique et ces incertitudes du ratio antiprotons sur protons sont réévalués et comparés aux données inédites de AMS-02. Aucune indication pour un excès n'est trouvé. Une préférence pour un halo confinant plus large et une dépendance en énergie du coefficient de diffusion plus plate apparaissent. De nouvelles contraintes sur l'annihilation et la désintégration de la MN sont ainsi dérivés.Les émissions secondaires des électrons et des positrons peuvent aussi contraindre l'annihilation et la désintégration de la MN dans le halo galactique : le signal radio dû à la radiation synchrotron des électrons et positrons dans le champs magnétique galactique, les rayons gamma des processus de bremsstrahlung avec le gas galactique et de Compton Inverse avec le champs radiatif interstellaire sont considérés. Différentes configurations de champs magnétique galactique et de modèles de propagation et des cartes de gas et de champs radiatif interstellaire améliorés sont utilisées pour obtenir des outils permettant le calculs des émissions synchrotrons et bremsstrahlung venant de MN de type WIMP. Tous les résultats numériques sont incorporés dans la dernière version du Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID).Une interprétation d'un possible excès dans les données de rayons gamma de Fermi-LAT au centre galactique comme étant dû à l'annihilation de MN en canaux hadronique et leptonique est analysée. Dans une approche de messagers multiples, le calcul des émissions secondaires est amélioré et se révèle être important pour la détermination du spectre pour le canal leptonique. Ensuite, les limites provenant des antiprotons sur l'annihilation en canal hadronique contraignent sévèrement l'interprétation de cet excès comme étant dû à la MN, dans le cas de paramètres de propagation et de modulation solaire standards. Avec un choix plus conservatif de ces paramètres elles s'assouplissent considérablement. / Overwhelming evidence for the existence of Dark Matter (DM), in the form of an unknownparticle filling the galactic halos, originates from many observations in astrophysics and cosmology: its gravitational effects are apparent on galactic rotations, in galaxy clusters and in shaping the large scale structure of the Universe. On the other hand, a non-gravitational manifestation of its presence is yet to be unveiled. One of the most promising techniques is the one of indirect detection, aimed at identifying excesses in cosmic ray fluxes which could possibly be produced by DM annihilations or decays in the Milky Way halo. The current experimental efforts mainly focus in the GeV to TeV energy range, which is also where signals from WIMPs (Weakly Interacting Massive Particles) are expected. Focussing on charged cosmic rays, in particular antiprotons, electrons and positrons, as well as their secondary emissions, an analysis of current and forseen cosmic ray measurements and improvements on astrophysical models are presented. Antiproton data from PAMELA imposes contraints on annihilating and decaying DM which are similar to (or even slightly stronger than) the most stringent bounds from gamma ray experiments, even when kinetic energies below 10 GeV are discarded. However, choosing different sets of astrophysical parameters, in the form of propagation models and halo profiles, allows the contraints to span over one or two orders of magnitude. In order to exploit fully the power of antiprotons to constrain or discover DM, effects which were previously perceived as subleading turn out to be relevant especially for the analysis of the newly released AMS-02 data. In fact, including energy losses, diffusive reaccelleration and solar modulation can somewhat modify the current bounds, even at large DM masses. A wrong interpretation of the data may arise if they are not taken into account. Finally, using the updated proton and helium fluxes just released by the AMS-02 experiment, the astrophysical antiproton to proton ratio and its uncertainties are reevaluated and compared to the preliminarly reported AMS-02 measurements. No unambiguous evidence for a significant excess with respect to expectations is found. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. New stringed constraints on DM annihilation and decay are derived. Secondary emissions from electrons and positrons can also be used to constrain DM annihilation or decay in the galactic halo. The radio signal due to synchrotron radiation of electrons and positrons on the galactic magnetic field, gamma rays from bremsstrahlung processes on the galactic gas densities and from Inverse Compton scattering processes on the interstellar radiation field are considered. With several magnetic field configurations, propagation scenarios and improved gas density maps and interstellar radiation field, state-of-art tools allowing the computaion of synchrotron and bremssttrahlung radiation for any WIMP DM model are provided. All numerical results for DM are incorporated in the release of the Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID). Finally, the possible GeV gamma-ray excess identified in the Fermi-LAT data from the Galactic Center in terms of DM annihilation, either in hadronic or leptonic channels is studied. In order to test this tantalizing interprestation, a multi-messenger approach is used: first, the computation of secondary emisison from DM with respect to previous works confirms it to be relevant for determining the DM spectrum in leptonic channels. Second, limits from antiprotons severely constrain the DM interpretation of the excess in the hadronic channel, for standard assumptions on the Galactic propagation parameters and solar modulation. However, they considerably relax if more conservative choices are adopted.