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The following thesis is the description and the analysis of time resolution measurements of the plastic scintillator protorypes bar with PMT (photomultiplier tube) readout, performed with a 31 MeV electron beam at the HZDR (Helmholtz-Zentrum Dresden-Rossendorf) [1]. Similar bars will be used as building blocks for the NeuLAND detector (new large area neutron detector) - a ToF (time of flight) wall within the R3B setup (Reactions with Relativistic Radioactive Beams [2]) at the future FAIR facility (GSI Darmstadt [3]). The superconducting ELBE (electron linear-accellerator for beams of high brilliance and low emittance) was used as an electron source. The scintillation material used was RP408.
Two series of measurements were made within three months. In the first series, three bars of different sizes (200 x 5 x 5 cm3; 200 x 3 x 3 cm3; 300 x 5 x 5 cm3, the latter was made by coupling one 100 cm bar with a 200 cm bar using silicon grease) were used in the experiment consecutively. They had one Hamamatsu R8619 photomultiplier tube with an active diameter of 22 mm attached to each side with silicon grease. A measurement with the 200 x 5 x 5 cm3 bar without silicon grease was also performed.
In the second series, two equal scintillator bars (270 x 5 x 5 cm3 with a 10 cm light guide) on each side were used. Measurements with and without silicon coupling as well as with two different types of PMTs (R8619 and R2059) were executed.
Time and charge signals were processed with the TACQUILA electronic board. The time resolution was measured with the very precise pulsed electron signal of the accelerator. The time resolution measurements resulted in ρ200x5x5 ~ 159 ps; ρ200x5x5,no silicon ~ 162 ps; ρ200x3x3 ~ 153 ps; ρ300x5x5 ~ 204 ps.
For the second date they resulted in ρR8619 ~ 149 ps; ρR8619, no silicon ~ 175 ps; ρR2059 ~ 141 ps.
More tests and analysis is required until the results are definite.
Within the present work, photodissociation reactions on 100Mo, 93Mo and 92Mo isotopes were studied by means of the Coulomb dissociation method at the LAND setup at GSI. Experimental data on these isotopes are important to explain the problem of the underproduction of the lighter p-nuclei - 92; 94Mo - within the models of the p-process nucleosynthesis. The reaction rates used in the nucleosynthesis calculations are usually obtained within the framework of the statistical model. In order to verify the model predictions and reduce the uncertainties, experimental measurements of the reaction cross sections are required. In particular, the data on (γ,n) reactions are of interest, since these reactions were shown to dominate the p-process flow in the molybdenum mass region.
As a result of the analysis of the present experiment, integrated Coulomb excitation cross sections of the 100Mo(γ,n), 100Mo(γ,2n), 93Mo(γ,n) and 92Mo(γ,n) reactions were determined. The measurement of the 93Mo isotope is particularly important, since this nucleus is unstable, and the corresponding cross section has not been measured before.
It should be emphasized that Coulomb dissociation is a unique tool to study photoninduced reactions on unstable nuclei, which is especially relevant in the context of nucleosynthesis network calculations. However, because of to the complexity of the data analysis procedure and a number of model assumptions that are required in order to extract the Coulomb excitation cross section from the data, one of the main aspects of this thesis was to verify the method by comparing the results with the previously published data obtained with real photon beams. Integrated cross sections of the 100Mo(γ,n) and 100Mo(γ,2n) reactions were directly compared to the data by Beil et al., obtained at Saclay with photons from positron annihilation, while an indirect comparison could be performed with a recent photoactivation measurement by Erhard and co-workers. A reasonable agreement was observed for the 1n channel: a scaling factor of 0.8 ± 0.1 between our result and Beil et al. data is consistent with the scaling factor of 0.89±0.09 reported by Erhard et al. between their data and Beil et al. data. Both results are in agreement with the scaling factor of 0.85 ± 0.03 recommended by Berman et al. for the data measured at Saclay on nuclei in the respective mass region. A somewhat lower factor of 0.61 ± 0.09 between the present data and Beil et al. data was obtained for the 2n channel. The discrepancy might be explained by both the substantial efficiency correction that has to be applied to the LAND data in the two-neutron case, as well as by an insufficiently accurate assumption that the Saclay neutron detector efficiency is energy- and multiplicity- independent.
A second important topic of the present thesis is the investigation of the efficiency of the CsI gamma detector. The calorimetric information that it delivers is essential to reconstruct the energy-differential cross section from the present measurement. The data taken with the gamma calibration sources shortly after the experiment were used for the investigation. In addition, a test experiment in refined conditions was conducted within the framework of this thesis. Numerous GEANT3 simulations of the detector were performed in order to understand various aspects of its performance. As a result, the efficiency of the detector was determined to be approximately a factor of 2 lower than the efficiency expected from the simulation. This result is consistent with several independent investigations, which were performed using different methods. At the same time, a remarkable agreement between the simulated and experimental data was achieved under assumption that the inefficiency of the detector is explained by the loss of data from a number of crystals, which are randomly chosen in each event according to their averaged performance ratio (the ”on-off” effect). The reasons for the observed malfunction are yet not fully clear. Regardless of the exact reason, in the present conditions a deconvolution of the measured data from the CsI response is not possible. Consequently, within the framework of this thesis, the results are presented in terms of integrated cross sections. A search for alternative methods of data interpretation, allowing to extract energy-differential information out of the available data, in currently ongoing.
In the more recent experiments at the LAND setup, where the Crystal Ball gamma detector was used as a calorimeter, the reconstruction of the energy-differential cross section with a reasonable resolution was already shown to be feasible. It means that, even considering the uncertainties of the present experiment of the order of 10%, the uncertainties of the statistical model predictions, which are on average estimated to be within a factor of 1.5-2, can already be constrained.
The analysis of the present experiment is still in progress. As a next step, Coulomb excitation cross section for 94Mo will be obtained. The 94Mo(γ,n) reaction cannot be studied by photoactivation, since the life time of the daughter nucleus is too long (4000 y). At the same time, this reaction plays a key role in the p-process nucleosynthesis.
The future of the LAND setup - the R3B setup1 at FAIR2 - will take advantage of a three orders of magnitude higher intensity of the radioactive beams [85], as well as of a completely new detector system. High-resolution measurements of the energy-differential cross sections will be possible for exotic nuclei, which were never accessible in the laboratory before. Such measurements will open great opportunities for nuclear astrophysics, allowing to obtain high-quality experimental data even for regions of the nuclear chart where the statistical model calculations are not applicable.
Im Rahmen dieser Arbeit wird ein Gammaspektroskopie-Aufbau unter Verwendung eines HPGe-Clover-Detektors zur Nutzung in Aktivierungsexperimenten charakterisiert und untersucht. Die für präzise Aktivitätsmessungen nach einer Aktivierung nötigen Effizienzen werden mit Hilfe der Eichquellen 60Co und 22Na unter Nutzung verschiedener Modi des Clover-Detektors abstandsabhängig errechnet. „Listmode“-Daten ermöglichen dabei eine „offline“-Verarbeitung. Begleitet werden die Messungen von aufwändigen Monte-Carlo-Simulationen in Geant4. Parallele Auswertungsmethoden erlauben einen genauen Vergleich zwischen simulierten und experimentellen Ergebnissen.
Der Karlsruhe 4π-Bariumfluorid-Detektor, entwickelt und aufgebaut Ende der Achtzigerjahre am Forschungszentrum Karlsruhe, ist ein effizienter Detektor für Gammastrahlung und bietet vielfältige Einsatzmöglichkeiten für kernphysikalische Experimente. Insbesondere für Experimente der nuklearen Astrophysik ist er geeignet, aber auch für die Forschung zur Entwicklung neutronengetriebener Reaktoren, zum Beispiel zur Transmutation radioaktiver Abfälle. Derzeit befindet sich der Detektor an der Goethe-Universität Frankfurt, wo er mit der sich dort in Entwicklung befindenden FRANZ-Neutronenquelle eingesetzt werden soll. Diese ermöglicht zum Beispiel Messungen von Wirkungsquerschnitten für den s-Prozess in astrophysikalisch relevanten Energiebereichen und bei hohen Intensitäten.
Diese Arbeit behandelt astrophysikalische Möglichkeiten die der Detektor bietet sowie dessen allgemeinen Aufbau und Eigenschaften. Es wurden eine Funktionsprüfung des Detektors, Messungen der Zeit- und Energieauflösung, Energiekalibration sowie kleine Optimierungen und Reparaturen durchgeführt.
Im Rahmen dieser Arbeit wurde die Messung von ψ(2S) Mesonen mit dem ALICE-Experiment am LHC untersucht. Das ψ(2S) gehört zur Familie der Charmonia und kann sowohl in Proton-Proton- als auch in Nukleon-Nukleon-Kollisionen erzeugt werden und ist daher ein wichiger Parameter in den Studien dieser. Die Rate, mit der ψ(2S) durch verschiedene Mechanismen erzeugt werden, liefert Informationen über den Ablauf der Kollision und ist ein hilfreicher Faktor bei der Suche nach dem Quark-Gluon Plasma. Da es sich beim ψ(2S) um ein Charmonium handelt, das in niedrigere Charmoniumzustände zerfallen kann, ist das Verständis des ψ(2S) ebenso für Studien anderer Charmonia, wie dem J/ψ(1S), relevant.
In der LEBT-Sektion der Frankfurter Neutronenquelle am Stern-Gerlach-Zentrum (FRANZ) befinden sich zur transversalen Fokussierung des Ionenstrahls vier Solenoide. Die ersten beiden dienen dem Einschuss in das ExB-Choppersystem, die letzten beiden dem Einschuss in die erste Beschleunigerstruktur, den Radiofrequenzquadrupol (RFQ). In numerischen Transportsimulationen konnte gezeigt werden, dass insbesondere der erste Solenoid einen hohen Füllgrad aufweisen wird, was zu Strahlaberrationen und damit zu einer unerwünschten Erhöhung der Strahlemittanz führen kann.
Um diesen Effekt zu untersuchen, wurden die Fokussier- und Abbildungseigenschaften des ersten FRANZ-Solenoides analysiert. Analytische Rechnung unter Verwendung der Twissparametertransformation wurden durchgeführt, numerische Simulationen mit einem idealisiertem und einem realistischem Magnetfeldverlauf gemacht und 2 Messaufbauten mit einer Volumenquelle, dem Solenoid und einer Schlitz-Gitter-Emittanzmessanlage realisiert, um gemessene mit analytischen und numerischen Daten vergleichen zu können. Die Parameter, die ausgewertet und verglichen wurden, sind die Lage der Emittanzellipse, die Emittanz im x-x'-Phasenraum und die normierten vierten Momente (Wölbung) im Ortsraum.