Dissertations / Theses: 'Nuclear astrophysic'

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MASHA, ELIANA. "ASTROPHYSICAL NUCLEAR REACTIONS ON NEON ISOTOPES AT LUNA." Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/899089.

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This thesis reports the direct measurements of the 22Ne(α,γ)26Mg and 20Ne(p,γ)21Na reactions at astrophysical energies of interest. The 22Ne(α,γ)26Mg reaction competes with the 22Ne(α,n)25Mg reaction which is the main source of neutrons for the s-process in low-mass Asymptotic Giant Branch and massive stars. At temperatures T < 300 MK where the (α,γ) channel becomes dominant, the rate of the 22Ne(α,γ)26Mg reaction is influenced by several resonances studied only indirectly. The first part of this thesis concerns the direct measurement of one of these resonances, Er = 334 keV, which so far was studied only indirectly leading to six orders of magnitude range of possible values for its resonance strength. The experiment has been performed at LUNA (Laboratory for Underground Nuclear Astrophysics) using the intense alpha beam of the LUNA 400 kV accelerator and a windowless gas target combined with a high-efficiency BGO detector. In the present study, an upper limit of 4.0·10−11 eV has been determined for the resonance strength. Taking into account these results, an up-dated 22Ne(α,γ)26Mg thermonuclear reaction rate was obtained and its role on the predicted 25Mg/26Mg ratio of a 5M⊙ AGBs was investigated. The data show a decrease by a factor of 15 of the intershell 25Mg/26Mg ratio. The 20Ne(p,γ)21Na is the slowest reaction of the NeNa cycle. It determines the velocity of the cycle and defines the final abundances of the isotopes synthesized in this cycle. The uncertainties on the NeNa cycle are affected by the 20Ne(p,γ)21Na reaction rate. The main goal of the second part of this thesis was the direct measurement of the Ecm = 366 keV resonance which dominates the total rate in the temperature range between 0.2 GK and 1 GK. The measurement has been performed at LUNA using the windowless gas target and two high-purity germanium detectors placed at different positions. This measurement allowed to reduce the uncertainty on the strengths of the 366 keV resonance from 18% to 7%. These results were used to update the 20Ne(p,γ)21Na reaction rate.

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GNECH, ALEX. "Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis." Doctoral thesis, Gran Sasso Science Institute, 2020. http://hdl.handle.net/20.500.12571/14971.

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Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of ${}^7$Li and ${}^6$Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to ${}^6$Li abundance and recently the $alpha$+d$ ightarrow$ ${}^6$Li + $gamma$ and the p+${}^6$Li$ ightarrow$${}^7$Be+$gamma$ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the ${}^6$Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and ${}^6$Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

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Marta, Michele. "The 14N(p,γ)O15 reaction studied at low and high beam energy." Forschungszentrum Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-93642.

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The Bethe-Weizsäcker cycle consists of a set of nuclear reactions that convert hydrogen into helium and release energy in the stars. It determines the luminosity of low-metal stars at their turn-off from the main-sequence in the Hertzsprung-Russel diagram, so its rate enters the calculation of the globular clusters’ age, an independent lower limit on the age of the universe. The cycle contributes less than 1% to our Sun’s luminosity, but it produces neutrinos that can in principle be measured on Earth in underground experiments and bring direct information of the physical conditions in the solar core, provided that the nuclear reaction rate is known with sufficient precision. The 14N(p,γ)15O reaction is the slowest reaction of the Bethe-Weizs¨acker cycle and establishes its rate. Its cross section is the sum of the contributions by capture to different excited levels and to the ground state in 15O. Recent experiments studied the region of the resonance at Ep = 278 keV. Only one modern data set from an experiment performed in 1987 is available for the high-energy domain. Both energy ranges are needed to constrain the fit of the excitation function in the R-matrix framework and to obtain a reliable extrapolated S-factor at the very low astrophysical energies. The present research work studied the 14N(p,γ)15O reaction in the LUNA (Laboratory for Underground Nuclear Astrophysics) underground facility at three proton energies 0.36, 0.38, 0.40MeV, and in Dresden in the energy range Ep = 0.6 - 2MeV. In both cases, an intense proton beam was sent on solid titanium nitride sputtered targets, and the prompt photons emitted from the reaction were detected with germanium detectors. At LUNA, a composite germanium detector was used. This enabled a measurement with dramatically reduced summing corrections with respect to previous studies. The cross sections for capture to the ground state and to the excited states at 5181, 6172, and 6792 keV in 15O have been determined. An R-matrix fit was performed for capture to the ground state, that resolved the literature discrepancy of a factor two on the extrapolated S-factor. New precise branching ratios for the decay of the Ep = 278 keV resonance were measured. In Dresden, the strength of the Ep = 1058 keV resonance was measured relative to the well-known resonance at Ep = 278 keV, after checking the angular distribution. Its uncertainty is now half of the error quoted in literature. The branching ratios were also measured, showing that their recommended values should be updated. Preliminary data for the two most intense transitions off resonance are provided. The presence in the targets of the other stable nitrogen isotope 15N with its well- known isotopic abundance, allowed to measure the strength of two resonances at Ep = 430 and 897 keV of the 15N(p,αγ)12 C reaction, improving the precision for hydrogen depth profiling.

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MARCELLI, LAURA. "PAMELA mission: in flight perfomances and preliminary measurements of nuclear abundances." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/639.

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L'esperimento PAMELA (acronimo per “Payload for Antimatter-Matter Exploration and Light nuclei Astrophysics”) ha come obiettivo principale la ricerca e lo studio dei raggi cosmici con particolare attenzione alla ricerca della componente di antimateria presente in essi sotto forma di particelle e nuclei (antiprotoni, 80 MeV - 190 GeV, e positroni, 50 MeV - 270 GeV) al fine di mettere in evidenza il contributo, se esistente, proveniente da una possibile sorgente di materia oscura. PAMELA inoltre ricercherà antinuclei primordiali (in particolare anti-elio) e servirà da verifica per i modelli di propagazione dei raggi cosmici attraverso una precisa ricostruzione dello spettro energetico delle antiparticelle e lo studio dei nuclei leggeri e dei loro isotopi. Inoltre investigherà i fenomeni connessi alla fisica solare e terrestre. PAMELA è allogiata, come carico pagante, in un container pressurizzato a bordo di un satellite russo per il telerivelamento Resurs-DK1. Tale satellite è stato lanciato nello spazio con un’orbita ellittica (350 - 600 km di altezza) e con un'inclinazione di 70.0 gradi dal vettore Soyuz-U il 15 Giugno 2006 dal cosmodromo russo di Baikonur in Kazakhstan. Lo strumento PAMELA è costituito da uno spettrometro magnetico, un sistema di tempo di volo (TOF, “Time Of Flight”), un calorimetro elettromagnetico ad immagine, un sistema di anticoincidenza, un rivelatore a scintillazione addizionale ed un rivelatore di neutroni. La combinazione di questi rivelatori permette una buona discriminazione delle antiparticelle su un fondo molto abbondante. La durata della missione è prevista essere di almeno tre anni, durante i quali verrà collezionata una statistica senza precedenti. Il limite inferiore nel rapporto anti-He/He è fissato essere inferiore a 10^(-7). Prima del lancio e durante i primi mesi da presa dati è stato sviluppato il software di Quick Look (per il monitoraggio in tempo reale) e per l'analisi dei dati. Inoltre sono state stimate le lunghezze di attenuazione e l'efficienza di trigger per il sistema di scintillatori del TOF nella configurazione di volo. I risultati preliminari del rapporto nucleare Boro/Carbonio nell'intervallo energetico da 200 MeV/n fino a 25 GeV/n sono stati ottenuti combinando i dati provenienti dal Calorimetro, dallo spettrometro magnetico e dal sistema di tempo di volo. Questa misura è molto importante per mettere vincoli ai parametri dei modelli cosmologici e, di conseguenza, per rendere più facilmente visibile una possibile piccola contaminazione da sorgenti primarie negli spettri degli antiprotoni e positroni. Una migliore conoscenza dei modelli di propagazione è fondamentale per la ricerca della materia esotica, come la materia oscura o antimateria prodotta in processi esotici, poichè una segnatura di tali processi può essere riconosciuta solamente conoscendo con ottima precisione i flussi di tali particelle prodotti dai canali convenzionali e i meccanismi di accelerazione e trasporto.
PAMELA (a “Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics”) experiment is a satellite-borne apparatus designed for precision studies of the charged particles in the cosmic radiation. The primary scientific goal is the study of the antimatter component of the cosmic radiation (antiprotons, 80 MeV - 190 GeV; and positrons, 50 MeV - 270 GeV) in order to search for evidence of dark matter particle annihilations. PAMELA will also search for primordial antinuclei (in particular, anti-helium), and test cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and studies of light nuclei and their isotopes. In addition, it will measure the light nuclear component of cosmic rays and investigate phenomena connected with Solar and Earth physics. PAMELA is installed inside a pressurized container attached to a Russian Resurs DK1 earth-observation satellite that was launched into space in an elliptical (350 - 600 km of altitude) orbit with an inclination of 70.0 degrees by a Soyuz-U rocket on June 15th 2006 from the Baikonur cosmodrome in Kazakhstan. The PAMELA apparatus comprises a magnetic spectrometer, a Time of Flight system, a silicon-tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail catcher scintillator and a neutron detector. The combination of these devices allows antiparticles to be reliably identified from a large background of other charged particles. The semipolar orbit (70.0°) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV - 190 GeV) and positrons (50 MeV - 270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio anti-He/He below 10^(-7). Before launch and during the first months of data taking, Quick Look Software (for mission monitoring in real time) and Data Analysis Software were developed. Furthermore measurements of the the light attenuation lengths and trigger efficiencies of the TOF scintillator system in the "flight" configuration were performed. Preliminary results of Boron to Carbon nuclear ratio in cosmic rays in the energy range from 200 MeV/n up to 25 GeV/n have been derived using combined data from Calorimeter, Tracker and TOF systems. This measurement is very important to put constraints to propagation parameters of cosmological models and, as a consequence, to make more easily visibile a possible small contamination from primary sources in antiprotons and positrons spectra. A better determination of the cosmic ray propagation is fundamental for the search of exotic matter, like dark matter candidates or antimatter produced in exotic processes, since the signature of such processes can be recognized only by knowing with great precision the fluxes due to the conventional production, acceleration and transport mechanisms.

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Szabo, Anthony Paul. "High energy emissions for astrophysical objects." Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phs996.pdf.

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Doherty, Daniel Thomas. "Experimental studies for explosive nuclear astrophysics." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/18022.

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In the ejecta from ONe novae outbursts nuclei up to A~40 are observed. The 30P(p,γ)31S reaction is thought to be the bottleneck for the production of all elements heavier than sulphur. However, due to uncertainties in the properties of key proton-unbound resonances the reaction rate is not well determined. In this thesis work, excited states in 31S were populated via the 28Si(4He,n) light-ion fusion-evaporation reaction and the prompt electromagnetic radiation was then detected with the GAMMASPHERE detector array. This γ-ray spectroscopy study, and comparisons with the stable mirror nucleus 31P, allowed the determination of the 31S level structure below the proton-emission threshold and also of the key proton-unbound states for the 30P(p,γ)31S reaction. In particular, transitions from key, low-spin states were observed for the first time. This new information was then used for the re-evaluation of the 30P(p,γ)31S reaction in the temperature range relevant for ONe novae. The newly calculated rate is higher than previous estimates implying a greater flux of material processed to high-Z elements in novae. Astrophysical X-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The 15O(α,γ)19Ne reaction is one reaction that allows breakout from these CNO cycle and into the rp-process to fuel outbursts. The reaction is expected to be dominated by a single 3/2+ resonance at 4.033 MeV in 19Ne, however, limited information is available on this key state. This thesis work reports on a pioneering study of the 20Ne(p,d)19Ne reaction in inverse kinematics performed at the Experimental Storage Ring (ESR) as a means of accessing the 4.033-MeV state in 19Ne. The unique background free, high luminosity conditions of the ESR were utilised for this, the first transfer reaction performed at the ESR. The results of this pioneering test experiment are presented along with suggestions for future measurements at storage ring facilities.

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Mumby-Croft, Paul David. "Tactic : A New Detector for Nuclear Astrophysics." Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507686.

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TABASSAM, UZMA. "A Pair Spectrometer for Nuclear Astrophysics Applications." Doctoral thesis, Università degli Studi di Camerino, 2012. http://hdl.handle.net/11581/401785.

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A spectrometer using two fully depleted silicon detectors (in a configuration) has been realized with the goal of directly measuring the production rate of the e+eâˆ’ pairs emitted in E0 transition of the 12C 16O reaction. This is a key reaction in nuclear astrophysics, which takes place during the He burning stage of red giant stars and thus regulates the carbon/oxygen abundance in the Universe. In particular, we are interested to determine the e+eâˆ’ pair cross section at energies below 2 MeV, where theoretical estimate is possible by using the R- matrix extrapolation. Experimental e+eâˆ’ pair emission data at this energy thus provides a valuable tool to validate such analytical approximate scheme. Resolution and efficiency measurements have been carried out using 241Am +239 Pu source, the Î± source, 32P,207 Bi Î² sources and the 19F(p, Î±)16O fusion evaporation reaction below 1 MeV on beam reaction at CIRCE tandem accelerator (Caserta, Italy). The results obtained approve to be in good agreement with our GEANT4 simulation.

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Ruiz, C. "Aspects of nuclear phenomena under explosive astrophysical conditions." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/11338.

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Luis, Hélio Fernandes. "Study of nuclear reactions relevant for astrophysics by Micro-AMS." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/11274.

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Dissertação para obtenção do Grau de Doutor em Física
This work of this thesis was dedicated to the application of the Micro-AMS(Accelerator Mass spectrometry with micro-beam) to the study of nuclear reactions relevant to Astrophysics, namely reactions involving the radioisotope 36Cl. Before this could be done, the system had to be installed, tested and optimized. During the installation and testing phase, several isotopes were measured, principally lead and platinum isotopes, which served to show the potential of this technique for applications to Material science and archeology. After this initial stage, the work with 36Cl began. 36Cl is one of several short to medium lived isotopes (as compared to the earth age) whose abundances in the earlier solar system may help to clarify its formation process. There are two generally accepted possible models for the production of this radionuclide: it originated from the ejecta of a nearby supernova (where 36Cl was most probably produced via the s-process by neutron irradiation of 35Cl) and/or it was produced by in-situ irradiation of nebular dust by energetic particles(mostly, p, a, 3He -X-wind irradiation model). The objective of the present work was to measure the cross section of the 35Cl(n,γ)36Cl nuclear reaction which opened the possibility to the future study of the 37Cl(p,d)36Cl and 35Cl(d,p)36Cl nuclear reactions, by measuring the 36Cl content of AgCl samples with Micro-AMS, taking advantage of the very low detection limits of this technique for chlorine measurements. For that, the micro-AMS system of the CTN-IST laboratory had to be optimized for chlorine measurements, as to our knowledge this type of measurements had never been performed in such a system (AMS with micro-beam). This thesis presents the results of these developments, namely the tests in terms of precision and reproducibility that were done by comparing AgCl blanks irradiated at the Portuguese National Reactor with standards produced by the dilution of the NIST SRM 4943 standard material. With these results the cross section of the 37Cl(n,γ)36Cl was calculated.

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Depalo, Rosanna. "The neon-sodium cycle: Study of the 22Ne(p,gamma)23Na reaction at astrophysical energies." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424304.

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The 22Ne(p,gamma)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle plays a crucial role for the synthesis of the elements with mass A = 20-25 in asymptotic giant branch stars, classical novae explosions and type Ia supernovae, where hydrogen burning occurs at high temperatures. The 22Ne(p,gamma)23Na thermonuclear reaction rate is highly uncertain because of a large number of poorly known resonances lying at astrophysical energies. This thesis reports on a new experimental study of the 22Ne(p,gamma)23Na reaction. In particular, two experiments have been performed to pin down the cross section of the proton capture on 22Ne: a measurement of the resonances at proton energies below 400 keV has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Gran Sasso (Italy), while a high-precision study of the resonances between 400 and 660 keV has been performed at the Helmoltz-Zentrum Dresden-Rossendorf (Germany). For the LUNA measurement, a windowless gas target filled with enriched 22Ne was used and the gamma rays emitted in the 23Na decay were detected by two high-purity germanium detectors. The experiment performed at LUNA led to the first detection of three previously unobserved resonances. Moreover, the decay schemes of the corresponding excited states of 23Na have been extended with the observation of new transitions. The LUNA measurement also allowed to reduce the upper limits on three unobserved resonances that represent the main source of uncertainty for the reaction rate. The HZDR experiment was performed with a 22Ne solid target and two high-purity germanium detectors surrounded by BGO anti-Compton shields. The target were prepared implanting 22Ne on a tantalum backing. The implantation was performed at the 200 kV high-current implanter of Legnaro National Laboratories (Italy). To improve the precision on the strengths of the resonances between 400 and 660 keV, the well known 22Ne(p,gamma)23Na resonances at 1279 keV and 478 keV were used for normalization. This measurement allowed to reduce the uncertainty on the strengths of the 436 keV and 638.5 keV resonances up to a factor of three. Moreover, the strength of the 661 keV resonance has been revised downward by one order of magnitude. Taking into account the new results, an updated thermonuclear reaction rate has been calculated. At the temperatures of classical novae explosions, the uncertainty on the reaction rate has been reduced by about one order of magnitude compared to the literature.
La reazione 22Ne(p,gamma)23Na fa parte del ciclo neon-sodio per il bruciamento dell' idrogeno. Il ciclo neon-sodio gioca un ruolo fondamentale per la sintesi degli elementi con massa A = 20-25 nelle stelle in fase di asymptotic giant branch, nelle esplosioni di novae di tipo classico e nelle esplosioni di supernovae di tipo Ia, dove il bruciamento di idrogeno avviene ad alte temperature. In particolare, la reazione 22Ne(p,gamma)23Na è la più incerta del ciclo neon-sodio. L'incertezza sulla sezione d'urto è dovuta al contributo, alle energie di interesse astrofisico, di un gran numero di risonanze. Alcune di queste risonanze non sono mai state osservate, per altre, invece, l'intensità è conosciuta con grande incertezza. Per misurare la sezione d'urto della 22Ne(p,gamma)23Na alle energie di interesse astrofisico, due esperimenti sono stati condotti nell'ambito di questa tesi: il primo, svolto con l'apparato sperimentale di LUNA, ha permesso di esplorare le risonanze di energia inferiore a 400 keV. Il secondo, invece, è stato svolto all'Helmoltz-Zentrum Dresden-Rossendorf (HZDR), in Germania, ed ha permesso di miglirare la precisione sulle intensità delle risonanze tra 400 e 660 keV. Per la misura svolta al Gran Sasso è stato usato un bersaglio di tipo gassoso senza finestre di ingresso e i fotoni emessi nel decadimento del 23Na sono stati osservati con due rivelatori al germanio. L'esperimento svolto a LUNA ha permesso di rivelare per la prima volta tre risonanze. Per queste risonanze sono stati osservati anche nuovi modi di decadimento gamma. Questo ha permesso di ampliare gli schemi di decadimento di letteratura. Questa misura ha permesso, inoltre, di ridurre di due ordini di grandezza i limiti superiori sulle intensità di tre risonanze la cui esistenza è tuttora dubbia. Per l'esperimento svolto all'HZDR è stato utilizzato un bersaglio solido di 22Ne e due rivelatori al germanio circondati da schermi anti Compton. I target sono stati realizzati all'impiantatore da 200 kV dei Laboratori Nazionali di Legnaro impiantando il 22Ne su una targhetta di tantalio. L'intensità delle risonanze tra 400 e 660 keV è stata misurata usando come riferimento le risonanze a 1279 keV e 478 keV, che sono intense e ben note. Questo esperimento ha permesso di ridurre l'incertezza sull'intensità della risonanza a 436 keV di un fattore tre, mentre, per la risonanza a 661 keV, è stata determinata un'intensità un ordine di grandezza inferiore rispetto alla letteratura. Il rate di reazione astrofisico è stato aggiornato tenendo conto dei nuovi risultati descritti sopra. Alle temperature caratteristiche delle esplosioni di novae di tipo classico, l'incertezza sul nuovo rate è un ordine di grandezza inferiore rispetto alla letteratura.

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Álvarez, Pastor José Manuel. "Focal plane detectors of a Laue lens telescope for Nuclear Astrophysics." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/83940.

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centenares de keV hasta unos pocos MeV), presenta un extraordinario potencial para comprender los procesos más extremos que tienen lugar en el Universo, como las explosiones estelares o los aceleradores de partículas. No obstante, a pesar de los enormes esfuerzos realizados por los observatorios de rayos gamma (en el pasado y en la actualidad), se requiere una mejora en la sensibilidad instrumental para aprovechar el enorme potencial científico contenido en este rango energético. Durante las dos últimas décadas se han buscado formas de mejorar la sensibilidad de los instrumentos, incrementando la eficiencia de los detectores y reduciendo el ruido instrumental (mediante sofisticados mecanismos de blindaje y técnicas de análisis). Con este objetivo, un enorme esfuerzo en innovación instrumental (construcción de prototipos y estudios numéricos) está siendo realizado por una comunidad creciente de científicos que se enfrentan al reto de preparar la próxima generación de telescopios de rayos gamma. En particular, son especialmente notables los avances logrados en los últimos años en el campo de la focalización de rayos gamma mediante lentes de difracción. Conceptualmente, una lente de rayos gamma reduciría drásticamente el ruido instrumental ya que concentra los fotones en un detector de pequeñas dimensiones (el ruido es proporcional al volumen del instrumento). Una lente de difracción, para observaciones en astrofísica nuclear, no es sólo un concepto teórico, sino una realidad, gracias principalmente al proyecto CLAIRE. Asimismo, el desarrollo de la tecnología para la focalización de rayos gamma ha incentivado el desarrollo de las diferentes tecnologías de detección. Un detector apropiado para el plano focal de una lente gamma, debe disponer de capacidad de imagen, proporcionar espectroscopia de alta resolución y medir la polarización de los fotones incidentes. El trabajo presentado en esta tesis comprende tanto la óptica de focalización como el detector del plano focal. Con respecto a la óptica, se presenta el ensayo realizado con el prototipo CLAIRE, mediante el cual se ha confirmado los principios de una lente de difracción. En cuanto al plano focal, esta investigación se ha desarrollado principalmente en el marco de estudio de las misiones espaciales GRI (2007) y DUAL (2010), propuestas a la ESA dentro del programa “Cosmic Vision 2015-2025”. En el marco de la misión GRI, se presenta una configuración para el detector del plano focal basado en detectores pixelados de Cd(Zn)Te, al tiempo que se investiga y desarrolla un primer prototipo de detector pixelado de CdTe. Cabe destacar que el sistema de detección propuesto fue registrado con éxito mediante una patente europea, y está siendo desarrollado para su aplicación en medicina nuclear. En relación a la propuesta DUAL, se presenta un estudio del ruido instrumental obtenido mediante simulaciones numéricas con el fin de precisar la sensibilidad del instrumento (basado en detectores de Germanio) propuesto en esta misión. Más allá de las tecnología consideradas en GRI y DUAL, una amplia variedad de detectores pueden ser explorados, bien para el plano focal de una lente de difracción o bien como sistemas de detección por sí mismos. En este sentido, se ha ampliado el espectro de tecnologías y se ha incluido un estudio sobre detectores basados en xenón líquido. En esta tesis se ha realizado un trabajo de investigación y desarrollo con tecnologías vanguardistas propuestas para la próxima generación de telescopios de rayos gamma. Esta instrumentación debe enfrentarse al reto de alcanzar la sensibilidad requerida para dar respuesta a las cuestiones aun no resultas por la astrofísica de rayos gamma en el rango de energía de las transiciones nucleares.
few MeV) has an extraordinary potential for understanding the evolving and violent Universe. In spite of the strong efforts accomplished by past and current instruments, in order to perform observations in this energy range, an improvement in sensitivity over present technologies is needed to take full advantage of the scientific potential contained in this energy range. In order to achieve higher sensitivities, γ-ray astronomy has been looking over the last decades for new ways to increase the efficiency of its instruments while reducing the background noise. With the objective of reducing or avoiding as much background as possible (through shielding mechanisms and data analysis techniques), a strong effort in innovation and design (build-up of prototypes and numerical simulations studies) is being conducted by a community facing the challenge of preparing the next generation of γ-ray telescopes. In particular, the progress achieved during the last decade on focusing optics based on Laue lenses is especially remarkable. Conceptually, a focusing telescope will reduce drastically the background noise by concentrating γ-rays onto a small size detector. Focusing γ-rays with a Laue lens is not just a theoretical concept, but a reality, mainly thanks to the development of a first prototype of Laue lens for nuclear astrophysics accomplished as part of the CLAIRE project. Moreover, the development of focusing optics during these years has also encouraged the development of new detector technologies. The focal plane detector of a focusing telescope should provide imaging capabilities, perform high-resolution spectroscopy and measure the polarization of the incident photons in order to achieve the ambitious scientific goals. The research presented in this thesis covers both main areas of a γ-rays telescope: focusing optics and focal plane detector. As far as the optics is concerned, a test of the lens CLAIRE was performed in order to confirm the principles of a Laue diffraction lens. Concerning the focal plane detector, theoretical and experimental studies with new detector technologies have been carried out. Our main research has evolved in the framework of two mission concept studies -GRI (2007) and DUAL (2010)- submitted to the ESA Calls for a Medium-size mission opportunity within the Cosmic Vision 2015-2025 program. As far as the GRI mission is concerned, a focal plane detector configuration based on Cd(Zn)Te pixelated detectors is proposed, whilst development and testing of a detector prototype is accomplished. It is noteworthy that the detector configuration was successfully registered under a European Patent and is being considered for applications in the field of nuclear medicine. Regarding the DUAL mission, simulations of the expected space radiation environment and the resulting detector activation were carried out in order to estimate the performances of the all-sky Compton telescope of DUAL (based on Germanium-strip detectors). The results show that DUAL could achieve, after two years of operation, a continuum sensitivity one order of magnitude better than any past and current observatory in the MeV energy range and up to a factor 30 of improvement with its Laue lens. Beyond the detector technology proposed for GRI and DUAL, a wide variety of technologies could be explored for the focal plane of a γ-ray lens mission as well as for a stand-alone detector. In this thesis a focal plane detector based on liquid xenon is also considered. This work faces the challenges of the next generation of γ-ray telescopes, where high performance γ-ray detectors are necessary to achieve the required sensitivity in order to answer several hot scientific topics of Gamma-ray astrophysics in the energy range of nuclear transitions.

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Lonardoni, Diego. "From Hypernuclei to Hypermatter: a Quantum Monte Carlo Study of Strangeness in Nuclear Structure and Nuclear Astrophysics." Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/368865.

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The work presents the recent developments in Quantum Monte Carlo calculations for nuclear systems including strange degrees of freedom. The Auxiliary Field Diffusion Monte Carlo algorithm has been extended to the strange sector by the inclusion of the lightest among the hyperons, the Î› particle. This allows to perform detailed calculations for Î› hypernuclei, providing a microscopic framework for the study of the hyperon-nucleon interaction in connection with the available experimental information. The extension of the method for strange neutron matter, put the basis for the first Diffusion Monte Carlo analysis of the hypernuclear medium, with the derivation of neutron star observables of great astrophysical interest.

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Al, Mamun Md Abdullah. "Nuclei, Nucleons and Quarks in Astrophysical Phenomena." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461.

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MASCARETTI, CARLO. "Open problems in neutrino astrophysics." Doctoral thesis, Gran Sasso Science Institute, 2020. http://hdl.handle.net/20.500.12571/15041.

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In my thesis I addressed a selection of the open problems in neutrino astrophysics. These open problems regard the fundamental properties of neutrinos, as well as their role as an astrophysical messenger, on which we focussed our efforts. In the context of solar neutrinos, the main contribution of my work concerns the luminosity constraint, a strict relation between the solar luminosity in photons and in neutrinos. Such relation is based on few assumptions, among which the stationarity of the Sun, and that 4He is the only accumulating nuclear specie. We reformulated the derivation of the luminosity constraint in a simpler and clearer way, and generalised it by including the contribution of other accumulating elements and of the variation of the solar gravitational potential. The resulting updated luminosity constraint is more general, accurate, and powerful at connecting pp and CNO neutrinos, which are of paramount interest for solar neutrino detectors and for solving the solar metallicity problem. Atmospheric neutrinos have been studied both as a product of cosmic rays and as a background to the cosmic neutrino analyses. Two primary cosmic-ray flux models have been defined by fitting the data by ARGO-YBJ and KASCADE-Grande, which measure the knee of p+He at, respectively, ~700 TeV and ~5 PeV. Two atmospheric neutrino fluxes have been computed using such primary models as input, and have been compared to the available data to discriminate the knee position. Unfortunately, the uncertainties on the data only allow to slightly favour the KASCADE-Grande knee. The potential of atmospheric neutrinos as a proxy for cosmic-ray physics was discussed. The previous work pushed me to assess the possibility to detect prompt neutrinos as well as to investigate their role in cosmic neutrino analyses. A cosmic neutrino flux model was built by combining the expectation on the neutrino spectrum produced in pp collisions in starburst Galaxies with the experimental result of the through-going muons analysis. Comparing the components of the neutrino spectra, it was clear that prompt neutrinos cannot be extracted from samples rich in νμ-induced events. The cascades dataset resulted to be the most promising, and the yearly rates of cascade events in IceCube due to all components (and flavours) of the neutrino spectrum were computed for 1 TeV ≤ Eν ≤ 10 PeV. Prompt neutrinos resulted to contribute to less than 3% of the total rate of shower-like events. The detection of prompt neutrinos could be feasible by studying inclined cascades with a higher energy threshold, so as to reduce the conventional background. Finally, it was concluded that the contribution of prompt neutrinos could cause the spectral difference between the fluxes resulting from the HESE and through-going muons analyses. This spectral tension has been investigated also in my first paper, in which the results of the IceCube analyses have been discussed on the basis of the common set of assumptions used to interpret them. In fact, the spectra resulting from the HESE and through-going muons dataset would not be in tension if the astrophysical signal were anisotropic and distributed differently from an unbroken power law. An alternative two-component astrophysical neutrino spectrum proved to be compatible with all IceCube data, and was used to compute the expected rates of events due to tau neutrinos (double cascades) and Glashow resonances. Double cascade events were the focus of my second paper, in which standard neutrino oscillations and the through-going muons spectrum were used to obtain the astrophysical flux of all neutrino flavours. These were convolved with the (analytically approximated) effective areas of IceCube, IceCube-gen2, and KM3NeT to compute the rates of double cascade events above 100 TeV. IceCube is predicted to be very close to the first detection of double cascade events, and the recent preliminary data by IceCube agree with such prediction. The non-observation of double cascade events would lead to new physics or to disproving the discovery of cosmic neutrinos.

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Malatji, Kgashane Leroy. "Nuclear level densities and gamma-ray strength functions in Ta isotopes and nucleo-synthesis of ¹⁸ᴼTa." University of the Western Cape, 2016. http://hdl.handle.net/11394/5321.

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>Magister Scientiae - MSc
Most stable and extremely low abundance neutron deficient nuclei with Z ≥ 34 are referred to as p-nuclei. Nearly all p-nuclei with A < 110 are most likely produced in the rp-process while almost all A > 110 are thought to be produced by the photodisintegration of s- and r- process seed nuclei. However, for some nuclear systems, these processes are not sufficient to explain their observed solar abundance. Results from calculations in ¹⁸ᴼTa generally provoke debates since several processes are able, sometimes exclusively, to reproduce the observed ¹⁸ᴼTa abundance in the cosmos, making it a unique case study. Some of the main sources of errors in the predicted reaction rates of ¹⁸ᴼTa arise due to the absence of nuclear data or due to large uncertainties in the nuclear properties such as the nuclear level densities (NLD) and gamma-ray strength functions (γSF) of ¹⁸ᴼ,¹⁸¹Ta. The NLD and γSF are primary ingredients for astrophysical reaction rate calculations based on the Hauser-Feshbach approach. These parameters need to be well understood to improve our understanding of ¹⁸ᴼTa production in astrophysical environments. In this thesis, new experimental data for the low-energy part of the γSF and NLD in ¹⁸ᴼ,¹⁸¹Ta were extracted, using the so-called Oslo method. An experiment was performed and the NaI(Tl) gamma-ray array and silicon particle telescopes at the Oslo cyclotron laboratory were utilized to measure particle-γ coincidence events from which the NLDs and γSFs are extracted below the neutron separation energy threshold Sn. A beam of ³He was used to populate excited states in ¹⁸ᴼ,¹⁸¹Ta through the inelastic scattering (³He,³He’𝛾) and the transfer reaction (³He,𝜶𝛾). Based on results from this measurements, the Maxwellian averaged (n, 𝛾) cross sections for the 179Ta(n, γ) and ¹⁸ᴼTa(n, 𝛾) reactions, at the s-process thermal energy of kT = 30 keV (i.e. a temperature of T = 3.5 × 10⁸ K) and p-process thermal energy of 215 keV (T = 2.5 × 10⁹ K), respectively, were computed with the TALYS reaction code. These results can be used to place the nuclear physics aspects of the large network abundance calculations on a solid footing and have potential to improve our understanding of the astrophysical processes and sites involved in the production of nature’s rarest isotope ¹⁸ᴼTa.
National Research Foundation (NRF)

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Harss, Boris Peter Mathias Sascha. "Development of a radioactive 17F beam and its use in nuclear astrophysics experiments." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962379883.

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Altana, Carmen Loredana. "The role of nanostructured targets in Laser-Produced Plasmas for Nuclear Astrophysics studies." Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3737.

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This PhD thesis documents the experimental study of plasmas produced from the interaction of a high-power laser in ns domain with nanostructured materials compared with ordinary bulk target. The study is focused on the effect of solid targets with different physical and geometric characteristics, and has the purpose to asses the effects of nanoscale structures in laser-matter interaction and in plasma formation. The motivation for these experiments arises from the fact that there is the possibility of producing plasmas with density and temperature characteristics suitable for nuclear fusion studies, relevant in astrophysics. The optimization of the specific characteristics of nanomaterials, containing metal nanowires, could lead to a stagnant, hotter and denser plasma and to implement the above mentioned studies successfully. The nanostructured targets used in this study are metamaterials consisting in aligned metal nanowires grown by electrodeposition into a porous alumina matrix, obtained on a thick aluminium substrate. These materials were developed with different length, diameter, metal and deposition technique in order to maximize absorption in the visible and IR wavelengths. Various diagnostics were employed for the characterization of the Laser Produced Plasma (LPP). In particular, an Intensified CCD camera in visible domain has been a useful diagnostic tools to understand the expansion dynamics of laser created plumes, by providing a two-dimensional snap shots of the three-dimensional LPP propagation. Depending upon the target material, the generated plume s ion emission features (velocity, flux) as well as plasma properties (temperature, density) are varied even at constant laser intensity. The use of a CCD-camera in X-rays domain has allowed to investigate the X-ray emissivity of laser-produced plasmas. By coupling the detector with an array of pinhole, spectral selection of X-ray emission has been implemented. The Time of Flight measurements have provided a technique to determine the velocity distribution of the plasma at large distances from the target surface, complementarily to velocity estimated by visible imaging close to target surface. Moreover, morphological analysis of craters formed for the laser irradiation was performed by using an optical microscope. The cross-analysis of various diagnostics has immediately showed the differences between an ordinary Al-bulk target and nanostructured materials: bulk aluminium plasma has shorter duration, X-ray flux and ablation efficiency than all other. Finally, preliminary investigations of ion energy spectra, obtained with a Thomson Parabola Spectrometer, were carried out to better understand the nuclear fusion process in a plasma. Temperature estimated are in good agreement with the occurrence of nuclear fusions. All these experimental evidences have taken a further step towards the application of laser driven nuclear reactions.

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Galaviz, Redondo Daniel [Verfasser]. "Systematic study of alpha-nucleus potentials for neutron-deficient nuclei and its astrophysical applications / Daniel Galaviz Redondo." Aachen : Shaker, 2004. http://d-nb.info/1172614768/34.

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20

Day, Francesca. "Astrophysical signatures of axion-like particles." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:215f6432-6dbb-4a16-80d8-3ad0bc76ec2d.

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The Standard Model of particle physics has enjoyed unprecedented success in predicting experimental results. However, evidence from astrophysical observations points to the existence of a dark sector of particles that interact only very weakly with the Standard Model. In this work, we search for dark sector signatures in X-ray telescope data. Much of this work concerns a class of hypothetical particles, the axion-like particle (ALP). ALPs are a theoretically well-motivated extension of the Standard Model. If ALPs exist, they may lead to intriguing astrophysical signatures: in the presence of a background magnetic field, ALPs and photons can interconvert. We could detect ALPs by searching for photon to ALP conversion. For example, photons produced by point sources in or behind galaxy clusters may convert to ALPs in the cluster's magnetic field. This could lead to observable spectral anomalies. Using this strategy, we place world leading bounds on the ALP-photon coupling. One potential signal of dark matter is an anomalous line in the spectra of galaxies and galaxy clusters. In 2014, an anomalous line was found at an energy of 3.5 keV. The nature and cause of this line is still under discussion. We analyse a scenario in which the 3.5 keV line arises from dark matter decay to ALPs, which interconvert with 3.5 keV photons in astrophysical magnetic fields. We further report an anomalous deficit at 3.5 keV in the spectrum of the Active Galactic Nucleus at the centre of the Perseus galaxy cluster. This motivates the study of a new model in which both features are caused by âfluorescent dark matterâ which resonantly interacts with 3.5 keV photons. We analyse observations of Perseus at 3.5 keV to date, and show that they are well explained by this model. Further theoretical and experimental work is needed to discover or exclude fundamental physics effects in X-ray spectra.

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Wallace, Jennifer Patrita. "Studies of the structure of the Tz = -1 Nuclei 20Na and 30S for explosive astrophysics." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8039.

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In explosive astrophysical environments such as novae, X-ray bursters and supernovae, conditions of extreme temperature and density are achieved. Under such conditions, both the rate of energy release and path of nucleosynthesis are governed by reactions on unstable nuclei. In this light, direct reaction studies using radioactive ion beams play a vital role in determining nuclear reaction rates. However, in the vast majority of cases, direct measurements are not possible and as such, indirect measurements are equally important for the understanding of the main reaction processes driving astrophysical events. In this thesis work, indirect studies of the astrophysically important 19Ne(p,γ)20Na and 29P(p,γ)30S reactions have been performed. For the first reaction, a β-delayed proton decay study of 20Mg was performed to gain information about the spin-parity assignment of the first key resonance above the proton emission threshold in the compound nucleus 20Na. This resonance is expected to dominate the 19Ne(p,γ)20Na reaction rate in explosive astrophysical environments and its identity has been under discussion for a long time, with J π = 1+ and 3+ assignments suggested. In the present study an upper limit on the β-decay branch to this state of 0.02% with a con dence level of 90% is reported. This is signi cantly more stringent than previous studies and makes a 1+ assignment highly unlikely, favouring instead a 3+ assignment. A 3+ assignment is predicted to have a signi cantly higher resonance strength and produce a proportionately higher 19Ne(p,γ)20Na reaction rate in X-ray burst conditions. The second study performed was a detailed gamma-ray spectroscopy study of the nucleus 30S. Excitation energies have been determined with improved precision over previous studies and the first,firm spin-parity assignments of key 29P + p resonant states, expected to dominate the 29P(p,γ)30S reaction in stellar scenarios, have been made. An evaluation of the 29P(pγ)30S reaction over the temperature range T = 0.06-2.5 GK shows that the 3+ and 2+ resonant states located at Er = 292.0(9) and 413.1(10) keV, respectively, dominate the 29P(p,γ)30S reaction rate in ONe novae, while the 413 keV resonance is expected to govern the rate in X-ray burster environments. These new, precise resonance energy measurements and firm spin-parity assignments have signi cantly reduced uncertainties in the 29P(p,γ)30S reaction in ONe novae and X-ray bursters. In particular, the reaction rate is now speci ed precisely enough for calculations of isotopic abundances in ONe novae ejecta.

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22

Laird, Alison M. "An investigation of the d(18Ne,19Ne*)p reaction and its astrophysical relevance." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/1755.

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The reaction 15 O(alpha; gamma) 19 Ne is one of the potential breakout reactions from the Hot CNO cycle to the rpprocess. As such, it may play an important role in nuclear astrophysics for the understanding of energy generation rates and the synthesis of protonrich nuclei in sites of explosive hydrogen burning, such as novae and Xray bursters. Experiments were performed at the radioactive ion beam facility, at LouvainlaNeuve, Belgium, to test the validity of measuring indirectly the 15 O(alpha; gamma) 19 Ne reaction rate. The method utilised was the population of ex cited states in 19 Ne and the observation of their ffdecay. Information on the alpha branching ratios of the states of astrophysical interest, just above the alpha threshold, allows the reaction rate to be calculated, provided other resonance properties, i.e. T , ER and J , are known. Excited states in 19 Ne were populated via an inverse 18 Ne(d,p) reac tion on a deuterated polyethylene target. The reaction and decay products were measured in an experimental set up that comprised three silicon strip detector arrays, with a total of 320 detector elements. Two experiments were performed at E lab = 44.1 MeV and E lab = 54.3 MeV. The recoiling protons tagged the populated state and the detection of a coincident ffparticle and heavy residue pair identified its decay. Branching ratios for several states in 19 Ne were determined, showing the viability of this experimental approach. Optical model parameters were de termined from 18 Ne elastic scattering on deuterons. DWBA calculations were performed and compared with experimental angular distributions to yield spectroscopic factors. The results were comparable with a previous meas urement using a stable beam, despite the significantly lower beam intensity, and indicated that, provided the necessary beam intensity was available, this method would allow the measurement of the alpha branching ratio of the reson ance of most astrophysical interest at 504 keV and thus the determination of the 15 O(alpha; gamma) 19 Ne reaction rate.

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Hubbard, Nicolas. "Studies of the nuclear structure of 12C and the astrophysical production of 23Na." Thesis, University of York, 2018. http://etheses.whiterose.ac.uk/20690/.

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Nuclear reactions can be used to study both the structure of the atomic nucleus, and to study the evolution of stars and the Universe. In this thesis two experiments are presented: one studying the astrophysical impact of the 23Na(a,p)26Mg reaction, and one studying the nuclear structure of 12C near the proton separation energy of 16 MeV. The 23Na(a,p)26Mg reaction is an important reaction affecting the abundances of 23Na and the radioisotope 26Al in massive stars. Before 2014 experimental and theoretical data on this reaction was of unknown uncertainty. A new direct measurement of the 23Na(a,p)26Mg reaction was performed at Aarhus University and with two other independent modern measurements of the 23Na(a,p)26Mg reaction a new combined experimental reaction rate has been calculated with an uncertainty of 30%, and the impact on 23Na and 26Al production has been modelled and the abundances constrained by this reaction. 12C is a light, stable, and well-studied nucleus with current research generally on clustering phenomena. It is therefore unusual that a narrow shell-model predicted state with spin-parity 0- has not been experimentally observed already. Excited states of 12C were populated via the 11B(3He,d)12C reaction at iThemba LABS in South Africa, and analysed through R-matrix theory. No 0- state was observed in the region predicted by the shell-model, but a likely 0- state has been identified above the proton separation energy, and a detailed analysis of its properties using R-matrix theory is presented.

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Mei, Bo [Verfasser], René [Akademischer Betreuer] Reifarth, and Yuri A. [Akademischer Betreuer] Litvinov. "Nuclear reactions for astrophysics with storage rings / Bo Mei. Gutachter: René Reifarth ; Yuri A. Litvinov." Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2014. http://d-nb.info/1071902482/34.

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Bradfield-Smith, William. "Measurement of the ¹⁸Ne(α,p)²¹Na reaction rate, and its implications for Nuclear Astrophysics." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/12614.

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Experimental work has been carried out at Louvain-la-Neuve to study the reactions ¹³N(α,p)¹⁶O and ¹⁸Ne(α,p)²¹Na in inverse kinematics with a gaseous helium target. The experimental method devised was tested using the reaction ¹³N(α,p)¹⁶O, as the cross section was calculable from data on ¹⁶O(p,α)¹³N[1,2,3,4], the inverse reaction. This test experiment showed that the experimental error obtainable in the deduction of the cross section resonance strength's was 30%, making the technique of practical use in the investigation of (α,p) reactions of interest to Nuclear Astrophysics. The reaction ¹⁸Ne(α,p)²¹Na, which is important as a break-out mechanism from the hot CNO cycle into the rp-process during explosive hydrogen burning, has been investigated, and values for the cross sections resonance strengths have been extracted from the experimental data. A stellar reaction rate, based only upon the observed resonances, has been calculated and compared with theoretical predictions[5]. A good agreement was obtained at and above a temperature of 2.5 10⁹K, whilst at lower temperatures the experimentally reaction rate obtained fell rapidly below the calculated value. This discrepancy was due to the fact that the theoretical calculation of the stellar reaction rate used resonances at energies below 2.5 MeV, not observed experimentally. At low temperature the reaction flux through these resonances dominates the stellar reaction rate. The experimental stellar reaction rate, though only a lower limit, has been applied to a one mass zone X-ray burst model[6]. This network calculation has shown that break-out via ¹⁸Ne(α,p)²¹Na is sufficient to trigger the burst for a type I X-ray burster, and allow mass to flow from the CNO region to the mass 100 region via the rp-process.

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Cota, Stephen A. "The astrophysics of nebulae and active galactic nuclear emission-line regions : new methods and applications /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541707918.

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27

Michelagnoli, Caterina. "The lifetime of the 6.79 MeV state in 15O as a challenge for nuclear astrophysics and gamma-ray spectroscopy: a new DSAM measurement with the AGATA Demonstrator array." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3426648.

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The determination of the thermonuclear reaction rates is a challenging task of nuclear astrophysics. In order to investigate this and other nuclear processes in the stellar medium, new techniques and new advanced setups for nuclear physics experiments are of vital importance. In this Thesis an advanced γ-ray spectroscopy system has been used in an experiment of astrophysical interest, that is a new Doppler shift attenuation measurement of the lifetime of the 6.79MeV state in 15O. An accurate measurement of this quantity is of paramount importance in the determination of the astrophysical S-factor and the derived cross section for the 14N(p, γ)15O reaction, the slowest one in the CNO cycle. The results of a new direct measurement of this nuclear level lifetime are discussed. The first excited states in 15O (and 15N) were populated via fusion-evaporation and Nucleon-transfer reactions of 14N on 2H (implanted at the surface of a ≈4 mg=cm2 Au layer) at 32MeV beam energy, provided by the XTU Tandem at the Legnaro National Laboratories. Gamma rays were detected with 4 triple clusters of the AGATA Demonstrator array, placed at backward angles, allowing to measure the angular distribution of the emitted γ rays in a continuous way. The energy resolution and position sensitivity of this state-of-the-art gamma spectrometer have been exploited to investigate lifetimes of nuclear levels in the ≈fs range via the Doppler Shift Attenuation Method. The deconvolution of the lifetime effects on the line-shapes of the gamma peaks from the ones due to the kinematics of the emitting nuclei has been performed by means of detailed Monte Carlo simulations of the gamma emission and detection. Coupled-channel calculations for the nucleon transfer process have been used for this purpose. Being one of the first experiments using this state-of-the-art γ ray spectroscopy tool, particular emphasis will be put in the description of the not trivial data replay and analysis, as well as the development of an ad hoc simulation tool. The comparison of experimental and simulated spectra of high-energy gamma-rays, de-exciting levels with lifetimes in the few fs range, will be shown for the 6.79MeV transition in 15O and for known cases in 15N, together with details of the chi-square analysis. Lifetime estimates for excited levels in 15N will be given and compared with previous results. The data analysis allows to give a new limit to the lifetime of the 6.79MeV state in 15O.
La determinazione della sezione d'urto delle reazioni termonucleari nelle stelle è una delle sfide più impegnative per l'astrofisica nucleare. Per comprendere questo ed altri processi nucleari che avvengono nel mezzo stellare sono fondamentali gli esperimenti di fisica nucleare con tecniche e strumentazioni sempre più avanzate. In questo lavoro di tesi, è stato utilizzato per la prima volta un apparato d'avanguardia per la spettroscopia gamma per un esperimento di interesse astrofisico e, cioè, una nuova misura della vita media dello stato a 6.79 MeV nel nucleo 15O, utilizzando il metodo del Doppler shift attenuato. Una determinazione accurata di questa quantità è, infatti, di estrema importanza per ricavare il fattore astrofisico S e la corrispondente sezione d'urto della reazione 14N(pγ)15O, la più lenta del ciclo CNO. Verranno quindi presentati e discussi i risultati di una nuova misura diretta della vita media dello stato in questione. I primi stati eccitati del nucleo 15O (e 15N) sono stati popolati attraverso i meccanismi di fusione-evaporazione e di trasferimento di nucleoni nella reazione 14N + 2H (impiantato sulla superficie di 4mg/cm2 di uno strato di oro) ad una energia di 32 MeV, con il fascio di 14N accelerato dal Tandem XTU dei Laboratori Nazionali di Legnaro. I raggi gamma prodotti nella reazione sono stati rivelati mediante quattro rivelatori compositi (clusters tripli) del dimostratore di AGATA, posti all'indietro rispetto alla linea di fascio, consentendo una misura, in modo continuo, della distribuzione angolare dei raggi gamma. La risoluzione in energia e la sensibilità alla posizione di interazione di questo modernissimo spettrometro gamma sono stati utilizzati per misurare vite medie nel range dei fs mediante il “Doppler Shift Attenuation Method". Il contributo degli effetti dovuti alla vita media sulle forme di riga dei picchi gamma, rispetto a quelli legati alla cinematica dei nuclei emessi è stato estratto mediante dettagliate simulazioni Monte Carlo della emissione e rivelazione della radiazione gamma. A questo scopo sono stati effettuati calcoli in canali accoppiati del processo di trasferimento di nucleoni. Trattandosi di uno dei primi esperimenti in cui tale spettrometro d’avanguardia è coinvolto, verranno discussi in dettaglio i vari passaggi dell’analisi dei dati e dello sviluppo di una parte di codice Monte Carlo. Il confronto tra gli spettri sperimentali e simulati per raggi gamma di energia molto alta, che diseccitano stati nucleari di pochi fs, verrà mostrato per la transizione di 6.79 MeV nel nucleo 15O e per alcuni livelli del nucleo 15N. Vengono presentati anche i dettagli dell’analisi del chi-quadro, essenziale per ottenere i risultati. I valori di vita media ottenuti per gli stati eccitati del nucleo 15N vengono confrontati con i risultati noti in letteratura. L’analisi dei dati conclusiva ha permesso di dare un nuovo limite alla vita media del livello a 6.79 MeV del nucleo 15O.

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28

Bemmerer, Daniel. "Precise nuclear physics for the Sun." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-95439.

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Abstract:

For many centuries, the study of the Sun has been an important testbed for understanding stars that are further away. One of the first astronomical observations Galileo Galilei made in 1612 with the newly invented telescope concerned the sunspots, and in 1814, Joseph von Fraunhofer employed his new spectroscope to discover the absorption lines in the solar spectrum that are now named after him. Even though more refined and new modes of observation are now available than in the days of Galileo and Fraunhofer, the study of the Sun is still high on the agenda of contemporary science, due to three guiding interests. The first is connected to the ages-old human striving to understand the structure of the larger world surrounding us. Modern telescopes, some of them even based outside the Earth’s atmosphere in space, have succeeded in observing astronomical objects that are billions of light- years away. However, for practical reasons precision data that are important for understanding stars can still only be gained from the Sun. In a sense, the observations of far-away astronomical objects thus call for a more precise study of the closeby, of the Sun, for their interpretation. The second interest stems from the human desire to understand the essence of the world, in particular the elementary particles of which it consists. Large accelerators have been constructed to produce and collide these particles. However, man-made machines can never be as luminous as the Sun when it comes to producing particles. Solar neutrinos have thus served not only as an astronomical tool to understand the Sun’s inner workings, but their behavior on the way from the Sun to the Earth is also being studied with the aim to understand their nature and interactions. The third interest is strictly connected to life on Earth. A multitude of research has shown that even relatively slight changes in the Earth’s climate may strongly affect the living conditions in a number of densely populated areas, mainly near the ocean shore and in arid regions. Thus, great effort is expended on the study of greenhouse gases in the Earth’s atmosphere. Also the Sun, via the solar irradiance and via the effects of the so-called solar wind of magnetic particles on the Earth’s atmosphere, may affect the climate. There is no proof linking solar effects to short-term changes in the Earth’s climate. However, such effects cannot be excluded, either, making it necessary to study the Sun. The experiments summarized in the present work contribute to the present-day study of our Sun by repeating, in the laboratory, some of the nuclear processes that take place in the core of the Sun. They aim to improve the precision of the nuclear cross section data that lay the foundation of the model of the nuclear reactions generating energy and producing neutrinos in the Sun. In order to reach this goal, low-energy nuclear physics experiments are performed. Wherever possible, the data are taken in a low-background, underground environment. There is only one underground accelerator facility in the world, the Laboratory Underground for Nuclear Astro- physics (LUNA) 0.4 MV accelerator in the Gran Sasso laboratory in Italy. Much of the research described here is based on experiments at LUNA. Background and feasibility studies shown here lay the base for future, higher-energy underground accelerators. Finally, it is shown that such a device can even be placed in a shallow-underground facility such as the Dresden Felsenkeller without great loss of sensitivity.

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29

Denke, Robson Zacarelli. "Fator S astrofisico para a reação de captura 4He(t,g)7Li pela investigação da reação de transferência elástica no sistema 7Li + 4He." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-30052007-170452/.

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Neste trabalho obtivemos o coeficiente de normalização da parte não ressonante da reação de captura 3H(alpha,gama)7Li (ou alternativamente, o fator S astrofísico) aplicando o método indireto ANC (Coeficientes de Normalização Assintótica) para a reação de transferência elástica do sistema 7Li + 4He. Essa reação de captura é de suma relevância na nucleosíntese de elementos leves no Universo primordial. Nesse método, o fator espectroscópico (ou alternativamente, o ANC) é obtido pela investigação de uma reação de transferência periférica que contenha como vértice a correspondente reação de captura. Reações de transferência têm normalmente dois vértices e um deles deve ser conhecido para que possamos obter o outro. No caso de uma transferência elástica, cuja característica é que o canal de saída elástico e de transferência são os mesmos, existe a vantagem da necessidade de consideração de apenas um vértice. Assim, uma análise combinada da distribuição angular para o espalhamento elástico 4He(7Li,7Li)4He, e para a reação de transferência 4He(7Li,4He)7Li, permitiu a extração do fator espectroscópico e consequentemente do ANC para o estado ligado <3He|4He>=7Li de uma forma única. As distribuições angulares para esses processos foram medidas no Laboratório Pelletron de São Paulo em duas energias de centro de massa 9.67 MeV e 10.62 MeV. Utilizamos nessas medidas feixes de 7Li obtidos no acelerador Pelletron com as energias de laboratório de 26.6 e 29.2 MeV. Empregamos um alvo gasoso de 4He e um sistema de colimadores de dupla-fenda na detecção. As partículas de 7Li espalhadas elasticamente e as partículas alfa da reação de transferência foram ambas detectadas em ângulos de laboratório diânteiros por um sistema de telescópios delta E - E com detectores de silício. Um código de simulação de Monte Carlo foi desenvolvido para calcular o ângulo sólido para esse sistema de fendas em ângulos próximos de zero grau. Um conjunto de parâmetros globais do Modelo Óptico foi obtido da análise das distribuições angulares do espalhamento elástico do sistema 7Li + 4He, juntamente com outras distribuições angulares obtidas da literatura em diferentes energias (~ 7-32 MeV). Os parâmetros do potencial óptico encontrados foram usados em uma análise de DWBA (Aproximação de Born de Ondas Distorcidas) para descrever a contribuição da reação de transferência de um tritio nas distribuições angulares. O fator espectroscópico obtido para o sistema ligado <3He|4He>=7Li foi S = 0.55+-0.03 e o coeficiente ANC C2 = 17.5 +- 1.0 fm-1. Com estes resultados, a seção de choque de captura para a reação 3H(alpha,gama)7Li e o respectivo fator S astrofísico foram calculados.
The normalization coefficient for the non-resonant part of the 3H(alpha,gama)7Li capture reaction (or alternately, the astrophysical S-factor) was obtained with the indirect method ANC (Asymptotic Normalization Coefficients). In this method the spectroscopic factor (or alternately, the ANC) is extracted from the investigation of a peripheral transfer reaction, which involves the same vertex as the corresponding capture reaction. Usually transfer reactions have two vertexes and the spectroscopic factor for one of them has to be known to obtain the other. In this work we investigate the 4He(7Li,4He)7Li elastic transfer reaction to obtain the spectroscopic factor and ANC for the 4He + t = 7Li bound system. The elastic transfer process, where the elastic and transfer exit channels are the same, has the advantage of having only one unknown vertex. Thus, the combined analysisof the angular distribution for elastic 4He(7Li,7Li)4He, and transfer process 4He(7Li,4He)7Li, allowed the extraction of the spectroscopic factor (and ANC) for the <3H|4He>=7Li bound system in an unique way. Angular distributions for these processes were measured at the Pelletron Laboratory at the center of mass energies of 9.67 MeV and 10.62 MeV. In these measurements, the 7Li beams with 26.6 MeV and 29.2 MeV were obtained from the Sao Paulo Pelletron accelerator. A 4He gas target and a double-slit collimator system were used. The 7Li scattered particles and alpha particles from transfer reaction were both detected at forward angles by a set of delta E - E silicon detectors telescopes. A Monte Carlo simulation code was developed to calculate the solid angle for the collimator system near the zero degree. A global optical potential parameters set for the 7Li + 4He system were defined using the measured elastic scattering angular distribution and other angular distributions obtained from the literature at different energies (from ~ 7-32 MeV). These optical potential parameters were used in the DWBA (Distorted Wave Born Approximation) analysis to describe the tritium transfer reaction contribution in the angular distributions. The obtained spectroscopic factor for the <3H,4He>=7Li bound system is S = 0.55+-0.03 and the ANC coefficient C2 = 17.5+-1.0 fm-1. With these results, the 3H(alpha,gama)7Li direct capture cross sections and astrophysical S-factor were calculated.

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30

Postnikov, Sergey A. "Topics in the Physics and Astrophysics of Neutron Stars." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1259174094.

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31

Curran, Dian Beard. "Magnetic shearing instabilities in accretion disks /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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32

Kafexhiu, Ervin [Verfasser], and Felix [Akademischer Betreuer] Aharonian. "Radiation signatures of nuclear reactions in very hot astrophysical plasmas / Ervin Kafexhiu ; Betreuer: Felix Aharonian." Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177380919/34.

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33

Rojas, Folkers Eduardo. "Evaluation, design, and construction of the Wallace Astrophysical Observatory Camera for astronomical observations." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54464.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, June 2009.
"May 2008." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 53-54).
The goal of this thesis is to upgrade the scientific capabilities of the 24" Cassegrain reflector telescope at the George R. Wallace, Jr. Astrophysical Observatory (Wallace Observatory), part of Massachusetts Institute of Technology (MIT). The upgrade consists of evaluating, designing and constructing the Wallace Astrophysical Observatory Camera (WAOcam), optimized for 24" telescope. A full 3D model of the 24" telescope and dome was created to find the size restrictions for WAOcam. An optical model was also developed to maximize the field of view of the camera detector. WAOcam was designed using SolidWorks (3D modeling Software), the parts files from the designing process were also used to machine the instrument. The manufacturing of the WAOcam involved using the following: Computer Numerical Control (CNC) lathe, CNC mill, drill press, and a Waterjet (cutting machine). The manufacturing process also required learning of Omax (software for the Waterjet) and MasterCam 9.1 (software for the CNC lathe and CNC mill). The resulting product is WAOcam, which consists of three modules: 1) vacuum dewar (houses a CCD detector), 2) shutter (controls when light hits the camera detector), and 3) filter wheel (modifies the light before hitting the detector). The remaining work left on the WAOcam is the installation of two additional modules: 1) a four port instrument rotator and 2) a field rotator. This upgrade will allow for occultation observations, strip scanning surveys, and Kuiper Belt Object (KBOs) astrometry to be obtained using the 24" telescope.
by Folkers Eduardo Rojas.
S.B.

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34

Bemmerer, Daniel. "Precise nuclear physics for the sun." Forschungszentrum Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-97364.

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Abstract:

For many centuries, the study of the Sun has been an important testbed for understanding stars that are further away. One of the first astronomical observations Galileo Galilei made in 1612 with the newly invented telescope concerned the sunspots, and in 1814, Joseph von Fraunhofer employed his new spectroscope to discover the absorption lines in the solar spectrum that are now named after him. Even though more refined and new modes of observation are now available than in the days of Galileo and Fraunhofer, the study of the Sun is still high on the agenda of contemporary science, due to three guiding interests. The first is connected to the ages-old human striving to understand the structure of the larger world surrounding us. Modern telescopes, some of them even based outside the Earth’s atmosphere in space, have succeeded in observing astronomical objects that are billions of lightyears away. However, for practical reasons precision data that are important for understanding stars can still only be gained from the Sun. In a sense, the observations of far-away astronomical objects thus call for a more precise study of the closeby, of the Sun, for their interpretation. The second interest stems from the human desire to understand the essence of the world, in particular the elementary particles of which it consists. Large accelerators have been constructed to produce and collide these particles. However, man-made machines can never be as luminous as the Sun when it comes to producing particles. Solar neutrinos have thus served not only as an astronomical tool to understand the Sun’s inner workings, but their behavior on the way from the Sun to the Earth is also being studied with the aim to understand their nature and interactions. The third interest is strictly connected to life on Earth. A multitude of research has shown that even relatively slight changes in the Earth’s climate may strongly affect the living conditions in a number of densely populated areas, mainly near the ocean shore and in arid regions. Thus, great effort is expended on the study of greenhouse gases in the Earth’s atmosphere. Also the Sun, via the solar irradiance and via the effects of the so-called solar wind of magnetic particles on the Earth’s atmosphere, may affect the climate. There is no proof linking solar effects to short-term changes in the Earth’s climate. However, such effects cannot be excluded, either, making it necessary to study the Sun. The experiments summarized in the present work contribute to the present-day study of our Sun by repeating, in the laboratory, some of the nuclear processes that take place in the core of the Sun. They aim to improve the precision of the nuclear cross section data that lay the foundation of the model of the nuclear reactions generating energy and producing neutrinos in the Sun. In order to reach this goal, low-energy nuclear physics experiments are performed. Wherever possible, the data are taken in a low-background, underground environment. There is only one underground accelerator facility in the world, the Laboratory Underground for Nuclear Astrophysics (LUNA) 0.4MV accelerator in the Gran Sasso laboratory in Italy. Much of the research described here is based on experiments at LUNA. Background and feasibility studies shown here lay the base for future, higher-energy underground accelerators. Finally, it is shown that such a device can even be placed in a shallow-underground facility such as the Dresden Felsenkeller without great loss of sensitivity.

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35

Röder, Marko. "Measurement of the Coulomb dissociation cross sections of the neutron rich nitrogen isotopes 20,21N." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-157725.

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Many neutron rich nuclei are involved in the astrophysical r-process (rapid neutron capture process). The r-process forms an important path for heavy element nucleosynthesis and runs along the neutron drip line. Astrophysicists suggested core-collapse supernovae within a neutrino-driven wind scenario where the neutrino wind dissociates all previously formed elements into protons, neutrons and α particles, to be a possible astrophysical scenario for the r-process. Furthermore, reaction network calculations reported a high impact of light neutron rich nuclei to the r-process abundance. Reactions on these exotic nuclei can only be studied with radioactive ion beams as their half lifes, in the order of a few hundred milliseconds (T1/2,19N=330ms), are too low to fabricate target material out of them. Two examples of reactions along the path of the r-process are the 19N(n,γ)20N and the 20N(n, γ)21N reactions. Using 20N (resp. 21N) as a beam, these reactions were studied at the GSI Fragment Separator (FRS) in time-reversed conditions via Coulomb dissociation in the S393 experiment exploiting the virtual gamma field of a lead target. The experiment was performed at the LAND/R3B setup (Large Area Neutron Detector, Reactions with Relativistic Radioactive Beams) in a kinematically complete measurement, i.e., detecting all particles leaving the nuclear reaction. The neutrons flying at relativistic velocity were observed by the LAND detector, the calibration of which plays a crucial role for the present reaction. The Smiley effect, meaning that the measured energy of impinging particles in long scintillators is not independent of the hit position of the particle, has been investigated. It will be shown that reflections of the light traveling through the scintillator and the resulting longer path length of the light when not emitted directly towards the ends of the bar were identified to cause the Smiley effect. Gamma spectra in coincidence with outgoing 19N (resp. 20N) were generated. These fit well to recent publications and were utilized to separate transitions of the projectile nucleus into the ground state or first excited state of the ejectile nucleus. The Coulomb dissociation cross section was calculated for the total reaction, transitions into the ground state and the first excited state of the ejectile nucleus. Furthermore, excitation energy spectra were derived for both reactions separately for ground state transitions and for the dominating transitions into the first excited state. In order to facilitate future experiments on exotic nuclei, two detector solutions for the NeuLAND detector (the successor of LAND) were investigated. Utilizing minimum ionizing electrons of 30MeV at the ELBE facility, time resolutions and detection efficiencies were studied for an MRPC (Multi-gap Resistive Plate Chamber) based neutron detector with passive iron converters, on the one hand, and a pure scintillator based neutron ToF detector on the other hand. The ELBE data show good time resolutions (σt,electron < 120 ps) and detection efficiencies (ǫelectron > 90%) for both systems. Small MRPC prototypes were irradiated with 175MeV quasi-monochromatic neutrons at The Svedberg Laboratory (TSL) in Uppsala measuring efficiencies of ǫMRPC,neutron = 1.0%. It will be shown that MRPCs with passive steel converters may be included as neutron detectors in experiments where a lower multi-neutron capability than the one needed for NeuLAND is sufficient
Viele neutronenreiche Kerne sind im schnellen Neutroneneinfangprozess (r-Prozess, engl. für rapid) involviert. Der r-Prozess bildet einen wichtigen Pfad für die Nukleosynthese schwerer Elemente und verläuft entlang der Neutronen-Dripline. Astrophysiker schlugen Kernkollaps-Supernovae innerhalb eines neutrinogetriebenen Windes als mögliches astrophysikalisches Szenario für den r-Prozess vor. Dabei werden alle zuvor gebildeten Elemente in Protonen, Neutronen und Alphapartikel dissoziiert. Außerdem ist von Berechnungen mit Reaktionsnetzwerken bekannt, dass leichte neutronenreiche Kerne einen hohen Einfluss auf die Elementverteilung des r-Prozesses haben. Reaktionen dieser exotischen Kerne können nur mit radioaktiven Ionenstrahlen studiert werden, da ihre Halbwertszeiten im Bereich von wenigen hundert Millisekunden (T1/2,19N=330ms) zu gering sind, um Probenmaterial daraus herzustellen. Zwei Beispiele solcher Reaktionen, die auf dem Pfad des r-Prozesses liegen, sind die 19N(n,γ)20N und die 20N(n,γ)21N Reaktionen. Unter Verwendung von 20N (bzw. 21N) als Strahl wurden diese Reaktionen am Fragment Separator (FRS) der GSI unter zeitumgekehrten Bedingungen mittels Coulomb-Aufbruch gemessen, indem das virtuelle Photonenfeld einer Bleiprobe ausgenutzt wurde. Das Experiment wurde am LAND/R3B Aufbau (Large Area Neutron Detector, Reactions with Relativistic Radioactive Beams) in einer kinematisch vollständigen Messung durchgeführt, d.h. alle ausgehenden Reaktionsprodukte wurden detektiert. Die relativistischen Neutronen wurden mit dem LAND-Detektor untersucht. Dessen Kalibration spielt eine wichtige Rolle für die hier analysierten Reaktionen. Dabei wurde der Smiley-Effekt studiert, welcher beinhaltet, dass die gemessene Energie von einfallenden Teilchen mittels langen Szintillatorstreifen nicht unabhängig von der Position ist, an der die Teilchen auf den Detektor treffen. Es wird gezeigt, dass Reflexionen des Lichtes beim Durchgang durch den Szintillator und die größere Weglänge, die das Licht zurücklegen muss, wenn es nicht direkt in Richtung der Enden des Szintillators emittiert wird, den Smiley-Effekt verursachen. Gamma-Spektren in Koinzidenz mit ausgehenden 19N (bzw. 20N) wurden gewonnen und stimmen gut mit früheren Veröffentlichungen überein. Diese Spektren wurden dazu verwendet, die Übergänge des Projektilkerns in den Grundzustand und den ersten angeregten Zustand des Ejektilkerns zu identifizieren. Die Wirkungsquerschnitte des Coulombaufbruchs der Projektilkerne und die Anregungsenergiespektren beider Reaktionen wurden berechnet und separiert in Übergänge in den Grundzustand und die dominierenden Übergänge in den ersten angeregten Zustand. Um künftige Experimente an exotischen Kernen zu ermöglichen, wurden zusätzlich zwei Detektorkonzepte für NeuLAND (Nachfolger von LAND) untersucht. Mit minimal ionisierenden Elektronen mit Energien von 30MeV aus dem Elektronenbeschleuniger ELBE wurden die Zeitauflösungen und Detektionseffizienzen zum einen für einen MRPC (Multi-gap Resistive Plate Chamber) basierenden Neutronendetektor mit passiven Stahlkonverter und zum anderen für einen reinen szintillatorbasierenden Neutronendetektor studiert. Die ELBE-Daten zeigen gute Zeitauflösungen (σt,electron < 120ps) und Detektionseffizienzen (ǫelectron > 90%) für beide Systeme. Kleine MRPC-Prototypen wurden mit quasi-monochromatischen Neutronen mit einer Energie von 175MeV am TSL (The Svedberg Laboratory) in Uppsala bestrahlt. Dabei wurden Effizienzen von ǫMRPC,neutron = 1.0% gemessen. Es wird gezeigt, dass MRPCs mit passiven Stahlkonvertern als Neutronendetektoren bei Experimenten, bei denen eine geringere Multineutronenfähigkeit als für NeuLAND ausreichend ist, eingesetzt werden können

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36

Williams, Robin James Richard. "The dynamics of active galactic nuclei." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318416.

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37

Sembay, S. F. "Continuum radiation from Active Galactic Nuclei." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377792.

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38

Wong, Yuen-lam. "Transient radiation emission from astrophysical jets." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39378512.

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39

Wong, Yuen-lam, and 黃菀林. "Transient radiation emission from astrophysical jets." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39378512.

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40

Chen, Guo-Xin. "Relativistic close coupling calculations for fundamental atomic processes in astrophysics." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078938510.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxvi, 249 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Anil K. Pradhan, Dept. of Astronomy. Includes bibliographical references (p. 237-249).

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41

Larsson, Josefin Boel Herta. "Black holes in high-energy astrophysics : active galactic nuclei and gamma-ray bursts." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612515.

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42

Santo, Marcelo Gimenez Del. "Estudo de reações nucleares de interesse astrofísico utilizando o método do cavalo de tróia." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-07042009-161106/.

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A Astrofísica Nuclear é a chave para explicar, entre outras coisas, a produção de energia nas estrelas, a evolução estelar e a síntese de elementos químicos e seus isótopos no Universo. Nesses casos, as reações nucleares formam a estrutura principal, cujas seções de choque e taxas de reação precisam ser determinadas com bastante precisão em laboratório. Devido às condições extremas encontradas nas estrelas, o entendimento dos processos nucleares que ocorrem em seus interiores se tornaram um grande desafio para os físicos nucleares teóricos e experimentais. Nos últimos 40 anos, os físicos vem medindo as taxas dessas reações, porém, as incertezas nesses valores são altas em razão das dificuldades experimentais encontradas nas medidas de seção de choque de processos que ocorrem em energias extremamente baixas (região do pico de Gamow). Desta forma, apenas em alguns casos é possível medir diretamente a seção de choque e o comportamento em baixas energias é geralmente extrapolado da região de energias mais altas. Para evitar o procedimento da extrapolação, alguns métodos indiretos estão sendo 5 usados com sucesso nos últimos anos. Em particular, o método do Cavalo de Tróia permite obter o fator astrofísico S(E) de reações nucleares envolvendo partículas carregadas a baixas energias sem necessidade de extrapolação e sem o efeito da blindagem eletrônica. As reações 10B(p,a)7Be e 11B(p,a)8Be são as principais responsáveis pela queima do boro em estrelas do grupo F e G da sequência principal. As respectivas seções de choque já foram obtidas em experimentos diretos anteriores, porém, os dados não chegam na região do pico de Gamow e o comportamento do fator astrofísico é extrapolado de energias mais altas. Neste trabalho, obteve-se o fator astrofísico S(E) das reações 10B(p,a)7Be e 11B(p,a)8Be através do método indireto do Cavalo de Tróia (THM) aplicado às reações de três corpos 2H(10B,a7Be)n e 2H(11B,a8Be)n sem necessidade de extrapolação. O fator astrofísico obtido por meio do THM para a reação 10B(p,a)7Be é duas vezes menor na região do pico de Gamow comparado com estudos diretos anteriores. Para a reação 11B(p,a)8Be foram estudados separadamente os canais a0 e a1 e o fator astrofísico obtido por meio do THM está de acordo com os estudos diretos anteriores.
Nuclear Astrophysics is the key to explain, among other things, the production of energy in stars, stellar evolution and the synthesis of chemical elements and isotopes in the Universe. In such cases, nuclear reactions are the main structure, where cross sections and reaction rates must be determined with reasonable accuracy in the laboratory. Because the extreme conditions found in stars, the understanding of nuclear processes that occur in their interiors have become a big challenge for theoretical and experimental nuclear physicists. In the last 40 years, physicists are getting the rates of these reactions but the uncertainty in these values are high due to difficulties found in the experimental cross section measurements at very low energies (Gamow peak region). Thus, only in some cases it is possible to measure directly the cross section and the behavior at low energies is usually extrapolated from the region of higher energy. To avoid the procedure of extrapolation, some indirect methods are being used successfully in recent years. In particular, the Trojan Horse Method gives the Astrophysics 7 S(E) factor of nuclear reactions involving charged particles at low energies without extrapolation and without electron screening effects. The reactions 10B(p,a)7Be and 11B(p,a)8Be are the main responsible for the burning process of boron inside F and G main sequence stars. The cross sections of these reactions have been obtained in previous direct experiments, but the data did not reach the Gamow peak and the behavior of the S(E) factor is then extrapolated from higher energies. In this work, we extract the S(E) factor for the reactions 10B(p,a)7Be and 11B(p,a)8Be through the indirect Trojan Horse Method (THM) applied to the three body reactions 2H(10B,a7Be)n e 2H(11B,a8Be)n without extrapolation. The astrophysical S(E)-factor for the 10B(p,a)7Be reaction was extracted by means of the THM and it is a factor 2 less in the Gamow peak if compared with previous direct studies. For the 11B(p,a)8Be reaction both a0 e a1 channels were studied by means of the THM and the astrophysical S(E)-factor extracted is in good agreement with direct previous studies.

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43

Ouyed, Rachid. "Numerical simulations of astrophysical jets from Kerplerian accretion disks /." *McMaster only, 1996.

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44

Sun, Ai-Lei. "Active Galactic Nuclei Feedback and Galactic Out ows." Thesis, Princeton University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10167547.

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Feedback from active galactic nuclei (AGN) is thought to regulate the growth of supermassive black holes (SMBHs) and galaxies. The most direct evidence of AGN feedback is probably galactic outflows. This thesis addresses the link between SMBHs and their host galaxies from four different observational perspectives. First, I study the local correlation between black hole mass and the galactic halo potential (the MBH – V_c relation) based on Very Large Array (VLA) HI observations of galaxy rotation curves. Although there is a correlation, it is no tighter than the well-studied M_BH – σ* relation between the black hole mass and the potential of the galactic bulge, indicating that physical processes, such as feedback, could link the evolution of the black hole to the baryons in the bulge. In what follows, I thus search for galactic outflows as direct evidence of AGN feedback. Second, I use the Atacama Large Millimeter Array (ALMA) to observe a luminous obscured AGN that hosts an ionized galactic outflow and find a compact but massive molecular outflow that can potentially quench the star formation in 10

6 years.The third study extends the sample of known ionized outflows with new Magellan long-slit observations of 12 luminous obscured AGN. I find that most luminous obscured AGN (L_bol > 10⁴⁶ ergs s^–1) host ionized outflows on 10 kpc scales, and the size of the outflow correlates strongly with the luminosity of the AGN. Lastly, to capitalize on the power of modern photometric surveys, I experiment with a new broadband imaging technique to study the morphology of AGN emission line regions and outflows. With images from the Sloan Digital Sky Survey (SDSS), this method successfully constructs images of the [OIII]λ5007 emission line and reveals hundreds of extended emission-line systems. When applied to current and future surveys, such as the Large Synoptic Survey Telescope (LSST), this technique could open a new parameter space for the study of AGN outflows. In summary, through multi-phase and multi-scale galactic outflows, AGN feedback can link the growth of SMBHs with the evolution of galaxies.

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45

Ng, Shao-Chin Cindy. "Cosmological models with quintessence : dynamical properties and observational constraints." Title page, table of contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phn5758.pdf.

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Bibliography: leaves 100-106. Studies different models of "quintessence", in particular, a quintessence arising from an ultra-light pseudo Nambu-Goldstone boson. Overviews dynamical properties for these models using phase-space analyses to study attractor and tracker solutions. Studies high-redshift type Ia supernovae constraints on these models. Studies the impact of a simple phenomenological model for supernovae luminosity evolution on the PNGB models and the potentials of a future supernovae data set to discriminate the PNGB models over the other quintessence models. Studies gravitational lensing statistics of high luminosity quasars upon the quintessence models.

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46

Barioni, Adriana. "Estudo da interação de núcleos de massa A=8 com alvo de carbono e da reação de captura 8Li(p,)9Be de interesse astrofísico." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-13102009-133215/.

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As distribuições angulares para os espalhamentos elásticos 12C(8Li,8Li) e l2C(\'BY8B) estudados neste trabalho foram medidas em dois laboratórios. A medida da distribuição angular para o espalhamento elástico 12C(8Li,8Li) foi realizada no Laboratório Pelletron da Universidade de São Paulo, em duas energias, a 20,6 MeV e 23,9 MeV. O feixe secundário de \'Li utilizado nesse laboratório foi produzido pelo sistema RIBRAS. A medida da distribuição angular para o espalhamento elástico 12C(8B,8B) foi realizada no laboratório de Estrutura Nuclear da Universidade de Notre Dame, nos Estados Unidos. O feixe secundário radioativo de 8B foi pelo sistema Twinsol com uma energia de 25,8 MeV. Os resultados para a seção de choque total de reação, obtidos a partir da análise do espalhamento elástico, foram incluídos em uma sistemática envolvendo outros núcleos estáveis e exóticos fracamente ligados e também núcleos fortemente ligados, espalhados elasticamente em alvo de 12C. OS dados obtidos da literatura foram reanalisados nos mesmos padrões utilizados na análise dos dados deste trabalho. As seções de choque de reação foram obtidas ajustando aos dados as seções calculadas utilizando o potencial de São Paulo. A análise permitiu concluir que não foi observado um aumento da seção de choque total de reação para os sistemas estudados, indicando que efeitos como breakup, não devem sèr importantes para esse sistema. Isso também pode ser comprovado pelos resultados de cálculos de ClICC (Coatinuum Discretized Coupled Channel) para as distribuições angulares de espalhamento elástico. A reação de transferência 12C(8Li,9Be)11B também foi medida neste trabaIho, simultaneamente ao espalhamento elástico 12C(8Li,8Li), a 23.9 MeV. A finalidade desse estudo era obter o fator espectroscópico para o sistema ligado (9Be|8Li + P) e assim calcular o fator-S astrofísico e também a taxa de reação para a reação de captura 8Li(p,y)9Begs. O fator espectroscópico encontrado nesse trabalho 1,22(28), foi obtido a partir de cálculos de DWBA (Distorted-Wave Born Approximation) com o programa Fresco e utilizado na normalização na seção de choque de captura 8Li(p,y)9Begs. O valor obtido para a profundidade do potencial de espalhamento 8Li+p foi de (40,1 +_ 1,6) MeV. A partir desses parâmetros foi possível calcular as curvas para o fator-S astrofísico e a taxa de reação de captura 8Li(p,y)9Be, cujo valor obtido para uma temperatura T9 = 1 foi de (ov) = 0,26+-0,07/0,06cm3mol-1s-1.
The measurements of the angular distributions for the elastic scatterings 12C(\'Li,\'Li) and 12C(8B,8B) reported in this work have been done in two laboratories. Those corresponding to the angular distributions for the elastic scattering 12C(8Li,8Li) were performed at two ene&ies, 20.6 MeV and 23.9 MeV, at the Pelletron Laboratory of the University of São Paulo. The *Li beam used in this laboratory had been produced in the RIBRASsystem. The measurements of angular distribution for the elastic scattering 12C(\'B,\'B) were performed at the Nuclear Structure Laboratory, at the University of Notre Dame, in the United States of America. The \'B beam was produced by the Twinsol system, at 25.8 MeV. The results obtained for total reaction cross section were included in a systematics\'together with other stable and exotic weakly bound nuclei and also with tightly bound ones, elastically scattered by 12C target. The data obtained from the literature were re-analised on the same framework of the data of this work. The reaction cross sections were obtained by fitting to the data, the cross secti\'ons calculated with the São Paulo potential. From the analysis one could conclude that no increase was observed in the total reaction cross section for the studied systems, indicating that effects, such as breakup, are not important for this system.

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47

Packham, Christopher Charles. "Near infrared imaging and polarimetry of active galactic nuclei." Thesis, University of Hertfordshire, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338568.

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48

Hanson, C. G. "The spectral shape and variability of active galactic nuclei." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374747.

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49

Lomant, Susannah E. "Calculations of nuclear cross sections and astrophysical S-factors for reactions induced by protons and alpha particles on isotopes of copper." Virtual Press, 1999. http://liblink.bsu.edu/uhtbin/catkey/1137475.

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Nuclear reactions induced by neutrons, protons and alpha particles on copper isotopes are being studied in an effort to understand the nucleosynthesis of elements in stars, specifically, the p-process. The p-process occurs toward the end of a star's life and produces those elements which have a high proton to neutron ratio, which are heavier than iron. Little is known about the nature of the p-process-inside stars. Isotopes of copper are studied since they are close in mass number to iron, which has the highest nuclear binding energy. Nuclear cross sections will be calculated for copper, as well as S-factors, which are important from an astrophysical point of view. These values are needed to calculate reaction rates which are the main ingredients for understanding nucleosynthesis.
Department of Physics and Astronomy

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50

Robinson, A. "A study of emission line variability in active galactic nuclei." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356433.

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Dissertations / Theses on the topic 'Nuclear astrophysic'

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