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In dieser Arbeit wurden die ersten Schritte unternommen um Elektronen aus den Zerfällen schwerer Quarks zu messen. Im Folgenden wird zunächst ein Überblick zum physikalische Hintergrund gegeben und der elliptische Fluss als Sonde zur Untersuchung des QGP motiviert. Anschließend werden der LHC und ALICE näher beleuchtet und die einzelnen Detektorsysteme, die für diese Analyse wichtig sind, vorgestellt. Im weiteren wird eine Methode zur Identifizierung von Elektronen vorgestellt und die Kontamination des Elektronensignals durch Hadronen bestimmt. Abschließend wird der elliptische Fluss eines von Hadronen bereinigten Inklusiv-Elektronen Spektrums bestimmt und ein Ausblick auf weitere Analyseschritte gegeben.
We have studied one-proton-removal reactions of about 500MeV/u 17Ne beams on a carbon target at the R3B/LAND setup at GSI by detecting beam-like 15O-p and determining their relative-energy distribution. We exclusively selected the removal of a 17Ne halo proton, and the Glauber-model analysis of the 16F momentum distribution resulted in an s2 contribution in the 17Ne ground state of about 40%.
Construction and commissioning of a setup to study ageing phenomena in high rate gas detectors
(2014)
In high-rate heavy-ion experiments, gaseous detectors encounter big challenges in terms of degradation of their performance due to a phenomenon dubbed ageing. In this thesis, a setup for high precision ageing studies has been constructed and commissioned at the GSI detector laboratory. The main objective is the study of ageing phenomena evoked by materials used to build gaseous detectors for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR).
The precision of the measurement, e.g., of the gain of a gaseous detector, is a key element in ageing studies: it allows to perform the measurement at realistic rates in an acceptable time span. It is well known the accelerating ageing employing high intensity sources might produce misleading results. The primary objective is to build an apparatus which allows very accurate measurements and is thus sensitive to minute degradations in detector performance. The construction and commissioning of the
setup has been carried out in two steps. During the first step of this work, a simpler setup which already existed in the detector laboratory of GSI had been utilised to define all conditions related to ageing studies. The outcome of these studies defined the properties and characteristics that must be met to build and operate a new, sophisticated and precise setup. The already existing setup consisted of two identical Multi Wire Proportional Chambers (MWPCs), a gas mixing station, an 55Fe source, an x-ray generator, an outgassing box and stainless steel tubing. In a first step, the gain and electric field configuration of the MWPCs were simulated by a combination of a gas simulation (Magboltz) and electric field simulation program (Garfield). The performance and operating conditions of the chambers have been thoroughly characterised before utilising them in first preparatory ageing test. The main diagnostic parameter in ageing studies is the detector gain, thus it is mandatory for precise ageing studies to minimise the systematic and statistical variation of the pressure and temperature corrected gain. To achieve the required accuracy, several improvements of the chamber design and the gas system have been implemented. In addition, the temperature measurement has been optimised. During the preparatory tests, several ageing studies have been carried out. The ageing effect of seven materials and gases have been carried out during these tests: RTV-3145, Ar/CO2 gas, Durostone flushed with Ar/Isobutane gas, Vetronit G11, Vetronit G11 contaminated with Micro 3000 and Gerband 705. The results of these studies went into the design of the new sophisticated ageing setup. For example some tests revealed that there was, even after cleaning, a certain level of contamination with "ageing agents" in the existing setup, which made it imperative to ensure a very high level cleanness of all components during the construction of the setup. The curing period of some testing samples like glues or the gas flow rate were found to be very important factors that must be taken into account to obtain comparable results. Very important changes in the chamber design have been made, i.e., the aluminium-Kapton cathodes used in MWPCs have been replaced with multi-wire planes and the fibreglass housing of the chamber has been changed to metal. The second step started with building the new setup which was designed based on the findings from the first step. The new ageing setup consists of three MWPCs, two moving platforms, an 55Fe source, a copper-anode x-ray generator, two outgassing boxes, both flexible and rigid stainless steel tubes. Before fabrication of the chambers, simulations of their electric field and the gain have been done using Magboltz and Garfield programs. After that, the chambers were installed and tested. A 0.3% peak-to-peak residual variation of the corrected gain has been achieved. Finally, the complete setup has been operated with full functionality in no-ageing conditions during one week. This test revealed very stable gain in all three chambers. After that two materials (Gerban 705 and RTV-3145) have been inserted in the two outgassing boxes and tested. They revealed an ageing rate of about 0.3%/mC/cm and 3%/mC/cm respectively. The final test proves the stability and accuracy of the ageing measurements carried out with the ageing setup at the detector laboratory at GSI which is ready to conduct the envisaged systematic ageing studies.
The subject of this thesis is the experimental investigation of the neutron-capture cross sections of the neutron-rich, short-lived boron isotopes 13B and 14B, as they are thought to influence the rapid neutron-capture process (r process) nucleosynthesis in a neutrino-driven wind scenario.
The 13;14B(n,g)14;15B reactions were studied in inverse kinematics via Coulomb dissociation at the LAND/R3B setup (Reactions with Relativistic Radioactive Beams). A radioactive beam of 14;15B was produced via in-flight fragmentation and directed onto a lead-target at about 500 AMeV. The neutron breakup of the projectile within the electromagnetic field of the target nucleus was investigated in a kinematically complete measurement. All outgoing reaction products were detected and analyzed in order to reconstruct the excitation energy.
The differential Coulomb dissociation cross sections as a function of the excitation energy were obtained and first experimental constraints on the photoabsorption and the neutron-capture cross sections were deduced. The results were compared to theoretical approximations of the cross sections in question. The Coulomb dissociation cross section of 15B into 14B(g.s.) + n was determined to be s(15B;14B(g:s:)+n) CD = 81(8stat)(10syst) mb ; while the Coulomb dissociation cross section of 14B into a neutron and 13B in its ground state was found to be s(14B;13B(g:s:)+n) CD = 281(25stat)(43syst) mb: Furthermore, new information on the nuclear structure of 14B were achieved, as the spectral shape of the differential Coulomb dissociation cross section indicates a halolike structure of the nucleus.
Additionally, the Coulomb dissociation of 11Be was investigated and compared to previous measurements in order to verify the present analysis. The corresponding Coulomb dissociation cross section of 11Be into 10Be(g.s.) + n was found to be 450(40stat)(54syst ) mb, which is in good agreement with the results of Palit et al.
Experiments for p-process nucleosynthesis with special focus on the most abundant p nucleus 92Mo
(2014)
This thesis describes experimental investigations and astrophysical network calculations relevant for the nucleosynthesis of the p nuclei. These 35 proton-rich isotopes cannot be produced by neutron-capture reactions which is the general production mechanism for elements heavier than iron in the r and s processes. Therefore, other mechanisms like photo-disintegration reactions on heavy seed nuclei (γ process) or proton-capture reactions are taken into account.
The modelling of these processes relies on a hugh amount of reactions which mostly occur for unstable isotopes. This demands, in combination with the contribution of excited states to the stellar rate, the prediction of the rates by a suited theoretical approach: the Hauser-Feshbach statistical model. To improve the reliability of the predictions, systematic experimental investigations are performed within this work for the nuclear input to the calculations. The study of charged-particle optical model potentials using the activation approach for the investigation of (α,n) and (p,n) reactions is described as well as the investigation of (γ,n) reactions in a broad mass range of 140 ≤ A ≤ 210.
However, there are also key reactions which are of special interest for the nucleosynthesis of individual p nuclei. An impressive example is the puzzle about the production of the most abundant p nucleus 92Mo. Within this work, the results of an experiment using high-resolution in-beam γ-spectroscopy for the study of the 90Zr(p,γ) reaction are summarized. In addition, the efforts to investigate the 91Nb(p,γ) reaction in standard kinematics by the production of target of the unstable isotope 91Nb to be used with the high-intensity proton-beam provided by the accelerator of FRANZ, Frankfurt, are discussed.
Finally, the influence of experimental results in astrophysical network calculations is discussed using post-processing nucleosynthesis methods for the γ process in type II supernovae.
Oscillations play a critical role in cognitive phenomena and have been observed in many brain regions. Experimental evidence indicates that classes of neurons exhibit properties that could promote oscillations, such as subthreshold resonance and electrical gap junctions. Typically, these two properties are studied separately but it is not clear which is the dominant determinant of global network rhythms. Our aim is to provide an analytical understanding of how these two effects destabilize the fluctuation-driven state, in which neurons fire irregularly, and lead to an emergence of global synchronous oscillations. Here we show how the oscillation frequency is shaped by single neuron resonance, electrical and chemical synapses.The presence of both gap junctions and subthreshold resonance are necessary for the emergence of oscillations. Our results are in agreement with several experimental observations such as network responses to oscillatory inputs and offer a much-needed conceptual link connecting a collection of disparate effects observed in networks.