Dissertationen: „Nuclear astrophysics“

1

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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3

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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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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5

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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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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Lonardoni, Diego. „From Hypernuclei to Hypermatter: a Quantum Monte Carlo Study of Strangeness in Nuclear Structure and Nuclear Astrophysics“. Doctoral thesis, University of Trento, 2013. http://eprints-phd.biblio.unitn.it/1068/1/PhD_Thesis_Lonardoni.pdf.

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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 Λ particle. This allows to perform detailed calculations for Λ 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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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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10

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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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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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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13

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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14

Mei, Bo [Verfasser], René [Akademischer Betreuer] Reifarth und 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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15

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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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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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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18

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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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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19

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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20

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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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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21

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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22

Singh, Bhivek. „The design and simulation of a new experimental set up to measure nuclear level lifetimes“. University of the Western Cape, 2016. http://hdl.handle.net/11394/5659.

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>Magister Scientiae - MSc
Measurements of nuclear level lifetimes are an important aspect of experimental nuclear physics. Such measurements determine transition matrix elements for nuclear structure research and also provide the widths of relevant excited states in nuclei that are of astrophysical interest. In the latter, the measured widths are used to obtain reaction rates in main sequence stars such as the Sun and in binary-star systems where the accretion of material from one star to another provides an opportunity to study extreme stellar environments such as novae and x-ray bursts. This thesis work describes the design and simulation of a new experimental set up at iThemba LABS that will allow for highprecision femtosecond-level lifetime measurements of nuclear states using the Doppler Shift Attenuation Method (DSAM). We use the Solid Edge computer-aided design (CAD) software to design a new scattering chamber with a cooled target ladder specifically for such measurements using inverse-kinematic transfer reactions with ion implanted targets. The light charged ejectiles from the reaction will be detected with a ΔE - E silicon telescope, while Doppler shifted rays will be registered using a high-purity and 100% efficient germanium (HPGe) detector. We also describe preliminary Monte Carlo simulation codes that are being developed in a relativistically invariant framework to optimize the experimental set up and to obtain predicted lineshapes of γ rays from several astrophysically relevant states in nuclei using this experimental set up.
National Research Foundation (NRF)

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23

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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24

De, Felice Antonio. „The accelerating universe and other cosmological aspects of modified gravity models“. Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2005. http://wwwlib.umi.com/cr/syr/main.

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25

Carriere, Josef. „Neutron stars and the equation of state of dense matter“. [Bloomington, Ind.] : Indiana University, 2005. http://wwwlib.umi.com/dissertations/fullcit/3183485.

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Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2005.
Source: Dissertation Abstracts International, Volume: 66-08, Section: B, page: 4269. Adviser: Charles J. Horowitz. Title from dissertation home page (viewed Oct. 10, 2006).

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26

Des, Jardins Angela Colman. „The topology of magnetic reconnection in solar flares“. Diss., Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/desjardins/DesJardinsA0807.pdf.

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27

Monroy, Raphael R. „The Effects of Superfluidity on the Oscillation Modes of Neutron Stars“. Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10830502.

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Oscillating single neutron stars are considered to be important quasi-continuous sources for gravitational wave emission and detection at the Laser Interferometer Gravitational-Wave Observatory (LIGO). In order to detect these oscillations above the noise level in the detector, LIGO data must be compared to theoretical templates of the signal, which means predicting the signal amplitude and frequency range. In this thesis, we compute the two most important eigenfrequencies of superfluid neutron stars where the signal might be peaked. To calculate this spectrum, we first construct the background structure of the neutron star using realistic microscopic models of dense and interacting nuclear matter. For this purpose, we use the CompOSE database which provides an array of such models with thermodynamically consistent interpolation. The fluid pertubation equations of the equilibrium configuration, including superfluidity in a two-fluid model, are solved numerically in the non-relativistic limit, yielding the eigenfrequencies upon imposing suitable boundary conditions. We find that the modes of the superfluid star support modes that are very close to the corresponding normal fluid star, but there also appear one or two purely superfluid modes, the lower one of which is intermediate between the two lowest order modes of the normal fluid. Thus, in the event that these oscillation modes can be observed, we can confirm the theoretical prediction of neutron superfluidity in neutron stars. A part of the results presented in this thesis have been published as a proceedings article in Jaikumar, Monroy and Klaehn, Universe 4, 58 (2018).

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28

Von, Oertzen Detlof Wilhelm. „The quark-hadron transition and hot hadronic matter in the early universe“. Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/15904.

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Includes bibliographical references.
Various calculations· of the evolution of the hadron gas in the early universe are carried out. To determine the starting point for the evolution equations a phase transition between the quark-gluon plasma phase and the hadron gas phase is constructed. A simple calculation leads to an estimate of the chemical potential of baryons at the quark-hadron phase transition in the early universe. We investigate how the transition temperature depends on the equations of state for the bagged quark and the hadron phase. A particle density evolution model is introduced which predicts the temperature at which particle species drop out of equilibrium (freeze-out) in an expanding universe. We then construct dynamical evolution equations to describe the reactions of interacting pions and photons. In order to model a more realistic hadron gas, we include kaons and finally nucleons and hyperons into the model universe. The results indicate that this type of model should be extended to include more interacting particle species and that a more realistic evolution model is dependent on obtaining accurate reaction cross-sections.

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29

Primulando, Reinard. „Dark matter in the heavens and at colliders: Models and constraints“. W&M ScholarWorks, 2012. https://scholarworks.wm.edu/etd/1539623601.

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In this dissertation, we investigate various aspects of dark matter detection and model building. Motivated by the cosmic ray positron excess observed by PAMELA, we construct models of decaying dark matter to explain the excess. Specifically we present an explicit, TeV-scale model of decaying dark matter in which the approximate stability of the dark matter candidate is a consequence of a global symmetry that is broken only by instanton-induced operators generated by a non-Abelian dark gauge group. Alternatively, the decaying operator can arise as a Planck suppressed correction in a model with an Abelian discrete symmetry and vector-like states at an intermediate scale that are responsible for generating lepton Yukawa couplings. A flavor-nonconserving dark matter decay is also considered in the case of fermionic dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, the cosmic-ray electron and positron spectra were studied. We show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. Motivated by a possible excess of gamma rays in the galactic center, we constructed a supersymmetric leptophilic higgs model to explain the excess. Finally, we consider an improvement on dark matter collider searches using the Razor analysis, which was originally utilized for supersymmetry searches by the CMS collaboration.

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30

Soltesz, Douglas Brandon. „Use of (³He,n) Reactions to Constrain Nuclear Reaction Rates in the Hydrogen and Helium Burning Environments of Type-I X-ray Bursts“. Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou161592153252756.

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31

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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32

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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33

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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34

Takács, Marcell Péter. „Hydrogen burning: Study of the 22Ne(p,gamma)23Na, 3He(alpha,gamma)7Be and 7Be(p, gamma)8B reactions at ultra-low energies“. Helmholtz-Zentrum Dresden - Rossendorf, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-233508.

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The neon-sodium cycle (NeNa cycle) of hydrogen burning is active in stars of the Asymptotic Giant Branch, in classical novae, and in supernovae of type Ia. The thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction is determined by a large number of resonances, and it represents the most uncertain rate in the NeNa cycle. This PhD thesis reports on an experiment to study tentative 22Ne(p,γ)23Na resonances at Elab = 71 and 105 keV, as well as the direct capture component of the reaction rate for Elab ≤ 400 keV. The measurements were performed deep underground at the Laboratory for Un- derground Nuclear Astrophysics - LUNA (Gran Sasso, Italy), taking advantage of the strong reduction in the cosmic ray induced background. The LUNA-400-kV electrostatic accelerator and a differentially pumped, windowless gas target of iso- topically enriched 22Ne gas were used. The γ-rays from the reaction were detected with a 4π bismuth germanate scintillator. The data show upper limits on the strengths of the resonances at Elab = 71 and 105 keV of 5.8 × 10−11 and 7.0 × 10−11 eV respectively. The resonances at Elab = 156.2, 189.5 and 259.7 keV have been re-studied and show 20% higher strength than the literature. The present experiment did not show any evidence for the direct capture process at the low energies studied. In addition to the experimental work at LUNA, the 3He(α, γ)7Be and 7Be(p, γ)8B reactions were studied using the most recent solar neutrino data available. Based on the standard solar model and the experimentally measured fluxes of solar 7Be and 8B neutrinos, the astrophysical S-factors of both reactions were evaluated directly in the solar Gamow peak.

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35

Kamil, Mohamed. „Spectroscopy of proton unbound states in 32Cl“. University of the Western Cape, 2019. http://hdl.handle.net/11394/6615.

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>Magister Scientiae - MSc
This project aimed to investigate proton unbound states in 32Cl using the 32S(3He; t) charge-exchange reaction. This research is relevant both in the context of nuclear structure and astrophysics. Excited states in 32Cl up to Ex 6 MeV were produced using a 50 MeV 3He++ beam from the K200 separated sector cyclotron at iThemba LABS. The triton ejectiles were mass analysed and detected at the focal plane of the K600 magnetic spectrometer. An additional segmented silicon detector array called CAKE was used to detect the unbound protons from states in 32Cl in conjunction with the tritons. In this work we looked for potential sources of isospin admixture that could explain the apparent violation of the Isobaric Multiplet Mass Equation (IMME) for the A = 32, T = 2 quintet. We also investigated the possibility of determining the 31S(p; ) reaction rate indirectly, via measurements of the partial proton widths of unbound states in 32Cl.

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Scott, David Andrew. „Underground study of the 17 O(p,γ )18F reaction at Gamow energies for classical novae“. Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9697.

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Classical novae are explained as thermonuclear explosions on the surface of white dwarf stars accreting hydrogen-rich material from less evolved companions in binary star systems. These events occur frequently within our galaxy and have been proposed as significant contributors to the galactic abundance of 13C, 15N, 17/18O and 18/19F. The short-lived isotope 18F (t1/2 = 110 min) is of particular importance since it may provide a signature of novae events through the detection of 511 keVγ-ray emission following the β+ decay of a 18F nucleus. During classical novae the 17O(p,γ)18F reaction governs the production of 18F and affects the synthesis of the rare isotopes mentioned above. Prior to the present study, the 17O(p,γ)18F reaction rate was poorly determined owing to a lack of low-energy experimental data. The present work reports on the first accurate measurements of the resonant and non-resonant contributions to the 17O(p,γ)18F reaction cross section in the energy region relevant for classical novae. Measurements were performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator facility of the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. Here the γ-ray background is suppressed by up to 3 orders of magnitude, thus providing a unique environment for low-energy measurements of reaction cross sections. Prompt γ rays associated with the formation and decay of states in 18F were analysed to determine the resonant and non-resonant contributions to the reaction cross section. The total non-resonant S-factor was determined at energies between Ecm ≈ 200 - 370 keV and the strength of a key resonance at Ecm = 183 keV was obtained with the best precision to date. The uncertainty in the reaction rate is now sufficiently low to place firmer constraints on nucleosynthesis predictions from accurate models of novae.

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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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Fortin, Morgane. „Evolution & dynamics of neutron stars : from microphysics to astrophysics“. Phd thesis, Observatoire de Paris, 2012. http://tel.archives-ouvertes.fr/tel-00731478.

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Les étoiles à neutrons sont le résidu d'étoiles massives et sont formées lors de la supernova qui marque de la fin de leur vie. Avec un rayon d'une dizaine de kilomètres pour une masse de une à deux fois celle du Soleil, elles sont des corps très denses et relativistes, supportés par l'interaction forte. Cette thèse traite de la modélisation théorique de trois aspects de la dynamique et de l'évolution des étoiles à neutrons : l'évolution thermique des étoiles à neutrons isolées et de celles accrétant de la matière d'une étoile compagnon, l'influence des propriétés élastiques de leurs parties solides sur la rotation des étoiles à neutrons isolées et l'évolution de la rotation des étoiles à neutrons accrétantes. La confrontation avec les observations permet de sonder les propriétés de la matière à haute densité.

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Reza, Katebi. „Nuclear Outbursts in the Centers of Galaxies“. Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1573031465540983.

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40

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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Caballero, Suárez Olga Liliana. „Effects of ion correlations in high density plasmas neutrino scattering and transport properties in supernovae and neutron star crusts /“. [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337248.

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Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008.
Title from PDF t.p. (viewed on Jul 29, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7583. Adviser: Charles J. Horowitz.

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Howard, Meredith E. „The Joy of CEX: Sharpening the (t,³He) probe at 345 MeV for the charge-exchange knife drawer“. Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1222168015.

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43

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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Zaballa, Robert Adrian. „Do R_{AA} and R_{CP} Quantify Nuclear Medium Effects?“ Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/28.

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With the use of an incoherent binary nucleon-nucleon collision model of heavy ion collisions for simulating particle production, it is demonstrated that the nuclear modification factors, R_{AA} and R_{CP}, are less than unity for hard scattering in the absence of any nuclear modification effects. The nuclear modification factor R_{dAu} is also shown to approach or exceed unity only if p_T broadening is taken into account. With a simple phenomenological parameter, the mean nucleon energy loss fraction, this model yields particle distributions that are comparable to those of experiment. The nuclear geometry is described by the Glauber model, and particle production is simulated by the PYTHIA event generator.

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Liu, Hang. „Studies of the Nuclear Three-Body System with Three Dimensional Faddeev Calculations“. Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1127332785.

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46

Subramanian, Mythili Myths. „Lifetimes of states in 19Ne above the 15O+ alpha threshold“. Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/792.

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Astrophysical models that address stellar energy generation and nucleosynthesis require a considerable amount of input from nuclear physics and are very sensitive to the detailed structure of nuclei, both stable and unstable. Radioactive nuclei play a dominant role in several stellar environments such as supernovae, X-ray bursts, novae etc. and nuclear data are important in the interpretation of these phenomena. When carbon, nitrogen and oxygen isotopes are present in substantial quantities in a star of sufficient mass, the fusion of four hydrogen nuclei to form a helium nucleus proceeds via the CNO cycles. Energy release in the CNO cycles is limited by the long lifetimes of 14O and 15O. In explosive stellar scenarios such as X-ray bursts, the energy output is very large, suggesting a breakout from the CNO cycles. 15O(α,γ)19Ne is the first reaction that breaks out of the CNO cycle. Nuclear structure information on high lying states in 19Ne is required to calculate the rate of the 15O(α,γ)19Ne reaction. This work focuses on the study of states in 19Ne above 3.53 MeV. The lifetimes of five states in 19Ne above 3.53 MeV were measured in this work. The states in 19Ne were populated via the 3He(20Ne,α)19Ne reaction at a beam energy of 34 MeV. The lifetimes were measured using the Doppler Shift Attenuation Method. The lifetimes of five states were measured and an upper limit was set on the lifetime of a sixth state. Three of the measurements are the most precise thus far. The lifetimes of the other three states agree with the values of the only other measurement of the lifetimes of these states. An upper limit on the rate of the 15O(α,γ)19Ne reaction was calculated at the 90% confidence level using the measured lifetimes. The contributions to the 15O(α,γ)19Ne reaction rate from several states in 19Ne at different stellar temperatures are discussed.

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Edelmann, Philipp [Verfasser], Friedrich K. [Akademischer Betreuer] Röpke und Alejandro [Akademischer Betreuer] Ibarra. „Coupling of Nuclear Reaction Networks and Hydrodynamics for Application in Stellar Astrophysics / Philipp Edelmann. Gutachter: Friedrich K. Röpke ; Alejandro Ibarra. Betreuer: Friedrich K. Röpke“. München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1048677184/34.

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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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Ujić, Predrag. „La réaction 78Kr ($/alpha$ , $/gamma$) d'intérêt astrophysique en cinématique inverse et l'effet d'écrantage électronique dans la décroissance bêta“. Phd thesis, Université de Caen, 2011. http://tel.archives-ouvertes.fr/tel-00648878.

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Cette thèse se compose de deux parties différentes qui s'inscrivent dans une thématique générale astrophysique. Les titres de ces parties sont : "La capture alpha en cinématique inverse liée au processus p ; mesure de la réaction 78Kr( $/alpha$ , $/gamma$ )82Sr "et "Mesures de la décroissance de 19O et 19Ne implantés dans le niobium ". L'objet de la première partie est directement liée à l'astrophysique nucléaire. Il s'agit d'établir une technique expérimentale pour la mesure directe à basse énergie de sections efficaces de réactions de capture radiative alpha en cinématique inverse. Ces réactions sont importantes en astrophysique, elles vont permettre d'améliorer les potentiels du modèle optique pour les particules alpha utilisés dans des modèles nucléaires pour prédire les sections efficaces des réactions ayant lieu dans les supernovae. Ici, nous avons insisté surtout sur la faisabilité technique de ce type d'expériences. En seconde partie de la thèse, on a examiné l'influence de l'environnement sur les probabilités de décroissance bêta d'un noyau, et en particulier de l'influence de l'écrantage électronique de la barrière de Coulombienne par les paires de Cooper d'un matériau supraconducteur. Un effet extrêmement faible, dans la limite des erreurs de mesure, aurait été observé.

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Piatti, Denise. „The Study of 22Ne(a,g)26Mg and 6Li(p,g)7Be Reactions at LUNA“. Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425392.

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In the current work the study of the 22Ne(a,g)26Mg and of the 6Li(p,g)7 Be reactions are presented. Both reactions were investigated at LUNA, located under 1400 m of Gran Sasso rock (Italy). The rock coverage guarantees an unprecedented reduction of the cosmic rays background. The 22Ne(a,g)26Mg reaction plays a fundamental role in the nucleosynthesis of s- nuclei in low-mass AGB stars and in massive stars. Indeed, the 22Ne(a,g)26Mg reaction is the competitor of the 22Ne(a,n)25 Mg reaction, an effective neutron source for element synthesis through s-process. The ratio between the rates of these two reactions is crucial to estimate the impact of AGB stars and massive stars on the s-nuclei abundances. Currently this ratio is affected by high uncertainty because of the wide range of values proposed for the 22Ne(a,g)26Mg 395 keV resonance strength (10^(-15) - 10^(-9) eV). All the results reported in literature are derived from indirect measurements. The present study represents the first direct measurement to estimate the strength of the 395 keV resonance and its impact on the 22Ne(a,g)26Mg reaction rate. Because of the low resonance strength values an high efficiency detector was installed at the gas target beamline of LUNA400kV accelerator, where the Ne gas, 99% enriched in 22Ne, was irradiated with a 399.9 keV a-beam. No significant signal was detected in the 22Ne(a,g)26Mg region of interest, thus an upper limit for the 395 keV resonance strength was estimated. The 6Li is an important indicator of the stellar age and of mixing processes in stars. Indeed it is progressively depleted by stars during the pre-main and main sequence phase via both 6Li(p,g)7Be and 6Li(p,a)3He reaction. The 6Li(p,g)7Be reaction was studied by many groups but a recent work renewed the interest on this reaction. A resonance like structure was observed at Ecm ~ 195 keV (Ex ~ 5.8 MeV) which is neither predicted by theoretical studies nor seen in previous experiments. The new excited state could explain the angular distribution of the 6Li(p,a)3He reaction, which requires both negative and positive parity levels contribution. In addition, the new excited state may affect the Standard Big Bang Nucleosynthesis predictions and the extrapolation to low energy of the 3He(a,g)7Be cross section. The present work has the goal of investigating the existence of the 195 keV resonance and of measuring the 6Li(p,g)7Be cross section down to low energies to better constrain the S-factor extrapolation at energies of astrophysical interest. The measurement was performed at the solid target beamline of LUNA400kV accelerator, where a devoted scattering chamber was installed. Six targets of different composition and thickness were irradiated at energies between 80 keV and 390 keV. In addition to the HPGe detector, used to detect gamma-rays produced by the 6Li(p,g)7Be reaction, a Si detector was put in place to detect the charged particles produced by the 6Li(p,a)3He reaction. The results of this thesis do not confirm the resonance observed at Ecm ~ 195 keV.
Nella presente tesi sono presentati gli studi sperimentali delle reazioni 22Ne(a,g)26Mg e 6Li(p,g)7Be. Entrambe le reazioni sono state studiate a LUNA, che si trova sotto 1400 m di roccia del Gran Sasso, per aver un'efficiente schermatura dal fondo creato dai raggi cosmici. La reazione 22Ne(a,g)26Mg ha un ruolo fondamentale per la nucleosintesi dei nuclei tramite il processo s in stelle AGB di piccola massa e nelle stelle massicce. Infatti essa compete con la reazione 22Ne(a,n)25Mg, un’efficiente sorgente di neutroni per il processo s. Il rapporto tra i rates di queste due reazioni è una quantità cruciale per stimare l’impatto delle stelle AGB e delle stelle massicce sulle abbondanze dei nuclei s. Attualmente questo rapporto non è noto con accuratezza poiché il contributo della risonanza a 395 keV della reazione 22Ne(a,g)26Mg è ancora incerto. Tutti i risultati di intensità riportati in letteratura per questa risonanza sono stati dedotti da misure indirette. Il presente lavoro si propone di studiare il contributo della risonanza a 395 keV sul rate della 22Ne(a,g)26Mg con una misura diretta. Poichè i valori di inten- sità per la risonanza stanno tra 10^(-15) eV e 10^(-9) eV un rivelatore ad alta efficienza è stato installato sulla linea gassosa collegata all’acceleratore LUNA400kV. Il gas Neon, arricchito al 99% in 22Ne, è sato irradiato con un fascio di particelle a con un energia di 399.9 keV. Nessun segnale significativo è stato rilevato nella regione energetica dello spettro di interesse per la reazione 22Ne(a,g)26Mg, perciò è stato calcolato un limite superiore per l'intensità della risonanza a 395 keV. Il 6Li è un importante indicatore dell'età stellare e dei processi di mescolamento nelle stelle. Infatti esso viene progressivamente distrutto dalle stelle nella fase precedente e durante la sequenza principale via le reazioni 6Li(p,a)3He e 6Li(p,g)7Be. La reazione 6Li(p,g)7Be è stata studiata da molti gruppi e un recente esperimento ha riacceso l’interesse per questa reazione. Una risonanza è stata osservata a Ecm ~ 195 keV (Ex ~ 5.8 MeV), né prevista da studi teorici né osservata in precedenti esperimenti. Il nuovo stato eccitato potrebbe però spiegare la distribuzione angolare della reazione 6Li(p,a)3He, che richiede il contributo sia di livelli con parità positiva e negativa. Inoltre, il nuovo stato eccitato potrebbe avere un effetto sulle predizioni della Standard Big Bang Nucleosynthesis e sull’estrapolazione a bassa energia della sezione d’urto della reazione 3 He(a,g)7Be. Lo studio attuale ha lo scopo di investigare l’esistenza della risonanza a 195 keV e di misurare la sezione d’urto della reazione 6Li(p,g)7Be fino a basse energie così da meglio estrapolare il fattore astrofisico, S(E), a energie di interesse astrofisico. La misura è stata svolta usando la linea solida dell’acceleratore LUNA400kV dove una camera di scattering dedicata è stata montata. Sei bersagli di diversa composizione e spessore sono stati irradiati a energie tra 80 keV e 390 keV. Assieme al rivelatore gamma HPGe, un silicio è stato usato per rivelare le particelle cariche prodotte dalla reazione 6Li(p,a)3He. I risultati di questa tesi non confermano la risonanza a Ecm ~ 195 keV.

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