| dc.description.abstract | One of the most challenging problems in nuclear astrophysics is answering a question about the origin and abundance of elements. There are numerous sites in the Universe where new elements can be created. In this particular work two types of extreme stellar environments are in focus: Novae and X-ray bursts. The peak temperatures achieved during a Nova explosion (ONe-type) is around 0.4*10^9 K, while for an X-ray burst this value can be of order of 10^9 K. Temperature is one of the major factors, which determines how far (by A mass number) the nucleosynthesis can go. While there are numerous reactions to consider in such environments, in this particular study the reaction ^34Cl(p,γ)^35Ar was investigated. ^34Cl has a relatively short halflife (1.5264(14) s) and can quickly decay into 34S. However this process competes with a reaction of proton capture 34Cl(p,γ)^35Ar, thus leaving a smaller amount of ^34Cl available for the decay to ^34S. The latter, on the other hand, is used for determining isotopic abundances in presolar grains that are extracted from meteorites. Typically, these grains have different isotopic ratios for sulphur than the one found in the Solar System. These differences can say something about the places where the pre-solar grains were synthesized. To be able to accurately predict isotopic abundances in Novae or X-ray bursts, the information about the rate of the reaction 34Cl(p,γ)^35Ar needs to be evaluated. That, in turn, requires some knowledge about the resonances in ^35Ar that lie just above proton threshold separation energy (Svp). The fact that only those resonances are important is dictated by the temperatures of the previously mentioned stellar environments. The Gamow window for a temperature of 0.4*10^9 K is located around 433 keV above Svp level in ^35Ar. An indirect method was used for populating the states above the proton separation energy, Svp, in ^35Ar. ^35K undergoes β+ -decay into ^35Ar and the Q-value of this reaction is sufficiently high to populate states above the Svp level. ^35Ar then decayed into ^34Cl + p. The spectroscopy of the levels decaying by protons was in the main focus of this work. The AstroBoxII is the detector used in this experiment. It allows low background noise measurements with high efficiency. Also HpGe detectors were used in coincidence with the AstroBoxII to be able to accurately distinguish between states in ^35Ar that decay either to the ground state or excited states in ^34Cl that then undergo a γ-emission. The major result of this thesis is the report of a new resonance at 6348(11) keV in ^35Ar. This resonance sits right in the middle of the Gamow window (for T=0.4*10^9 K) and potentially can have a big impact on the reaction rate of ^34Cl(p,γ)^35Ar. The estimate for the reaction rate dependence as a function of temperature is given in the Conclusions chapter. | en |
