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[en] For the measurement of neutron capture cross sections of noble gases a new experimental technique was developed using high pressure gas targets. By this technique, measurements on five krypton samples with different isotopic composition were performed by which the capture and the total cross sections between 5 and 200 keV were determined in the same experiment with good statistical accuracy. Values of Maxwellian averaged capture cross sections at 30 keV could be derived for the stable isotopes of krypton, as they are required for a quantitative understanding of the s-process of nucleosynthesis. From the systematics of this s-process it was possible to determine the original abundance of krypton in the solar system. The branching of the s-process at Se-79 allowed to determine the temperature of the s-process. A value of kT = 35 keV is adopted by this calculation. (orig.) 891 KBE/orig. 892 HIS

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[en] The neutron capture cross sections of natural Kr, ₈₄Kr and three samples enriched in ₈₃Kr, ₈₂Kr, and ₈₀Kr were measured with the time-of-flight technique in the energy range between 3 and 250 keV. The energy resolution was 1.5 ns/m. Capture gamma rays were detected by two C⁶D⁶ detectors using the pulse height weighting technique off-line. From these data, Maxwellian averaged cross sections < sigma v >/v_T have been determined for all stable Kr isotopes with an accuracy of typically 10 %, except for ₇₈Kr and ₈₆Kr, where the uncertainties are 30 % and 100 %, respectively. In addition, the cross sections for all s-process isotopes of Se, Br, and Kr were calculated with a Hauser Feshbach formalism with width fluctuation corrections, using carefully evaluated level densities and radiative decay widths. In the calculations all available experimental information about these cross sections was considered to include the local behavior of parameters. With this improved set of cross sections, the solar system abundance of Kr was determined from s-process systematics

[en] A flux detector system was developed in order to determine the fast neutron flux between 1 and 30 MeV obtained with the Karlsruhe isochronous cyclotron. The counter system represents a telescope-like proton recoil device using solid radiators and gas scintillation transmission counters. Flux determination is accomplished separately between about 1 to 6 MeV and approximately 5 to 30 MeV, with a small energy interval of overlap. Below 6 MeV, recoil protons are detected in a single gas scintillation chamber viewed by three photomultipliers requiring a fast coincidence. Above this range, high energy recoil protons are identified by coincidences in three adjacent chambers and by their specific energy losses. Since the transmission of the entire flux counter system is better than 99 percent, it can be used for simultaneous flux measurements in partial cross section determination. The accuracy for the determination of the neutron flux is about 5 percent

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[en] The input data for an analysis of the s-process branching at ⁷⁹Se have been significantly improved. The neutron capture cross sections for the stable krypton isotopes (except ⁸⁶Kr) were measured between 3 and 240 keV neutron energy. In addition, statistical model calculations of the (n,γ)-cross sections for all isotopes involved in this branching were performed. With these data and with other experimental results from literature a recommended set of Maxwellian average cross sections was established in the mass region 77< A<85. The relevant decay parameters of the involved unstable nuclei and the parameters for the s-process model are discussed as well. On this basis the following aspects are investigated: the temperature during s-process, the decomposition into s- and r-process contributions and the solar krypton abundance. (orig.)

No abstract available