30 research outputs found

    The new p-process database of KADoNiS

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    The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an online database (www.kadonis.org) for cross sections relevant to the s-process and the p-process. The first version was an updated sequel to the previous Bao et al. [1] compilations from 1987 and 2000 for (n; g) cross sections relevant to Big Bang and s-process nucleosynthesis. The first update, KADoNiS v0.2, was published in 2006 [2]. It contained mainly Maxwellian averaged (n; g) cross sections relevant to the s-process, and some experimental charged particle induced reaction relevant to the p-process. After that a second update was presented in 2009 [3]. Recently, we started to collect and review all existing experimental data relevant for p-process nucleosynthesis and to provide a user-friendly database based on the KADoNiS framework. The p-process part of the KADoNiS database is currently being extended and will include all available experimental data from (p; g), (p;n), (p;a), (a,g), (a;n) and (a; p) reactions in or close to the respective Gamow window

    Neutron capture cross section of 139 La

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    The neutron capture cross section of 139La{}^{139}\mathrm{La} has been measured relative to that of 197Au{}^{197}\mathrm{Au} by means of the activation method. The sample was irradiated in a quasistellar neutron spectrum for kT=25keVkT=25\mathrm{keV} generated via the 7Li(p,n)7Be{}^{7}\mathrm{Li}{(p,n)}^{7}\mathrm{Be} reaction with the proton energy adjusted 30 keV above the threshold. Maxwellian averaged neutron capture cross sections were calculated for energies kT=5‚ąí‚ąí100keV.kT=5--100\mathrm{keV}. The new value for kT=30keVkT=30\mathrm{keV} is found to be 31.6\ifmmode\pm\else\textpm\fi{}0.8\mathrm{mb}, 18% lower and considerably less uncertain than the previously recommended value of 38.4\ifmmode\pm\else\textpm\fi{}2.7\mathrm{mb}. With these results the s- and r-process components could be more accurately determined, making lanthanum a reliable s- and r-process indicator in stellar spectroscopy

    Neutron capture cross sections of 69Ga and 71Ga at 25 keV and e peak = 90 keV

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    This project was supported by EFNUDAT, ERINDA, the EuroGENESIS project MASCHE, HIC for FAIR and BMBF (05P15RFFN1).We measured the neutron capture cross sections of 69Ga and 71Ga for a quasi-stellar spectrum at kBT = 25 keV and a spectrum with a peak energy at 90 keV by the activation technique at the Joint Research Centre (JRC) in Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction 7Li(p,n). The produced activity was measured via the ő≥ emission of the product nuclei by high-purity germanium detectors. We present preliminary results.publishersversionpublishe

    First Measurement of the 96^{96}Ru(p,ő≥\gamma)97^{97}Rh Cross Section for the p-Process with a Storage Ring

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    This work presents a direct measurement of the 96^{96}Ru(p,ő≥p, \gamma)97^{97}Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating 96^{96}Ru ions interacted repeatedly with a hydrogen target. The 96^{96}Ru(p,ő≥p, \gamma)97^{97}Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the ő≥\gamma-ray strength function as well as the level density model can be pinned down with the measured (p,ő≥p, \gamma) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the ő≥\gamma-ray strength function and the level density have been removed. As a result, a constrained 96^{96}Ru(p,ő≥p, \gamma)97^{97}Rh reaction rate over a wide temperature range is recommended for pp-process network calculations.Comment: 10 pages, 7 figs, Accepted for publication at PR

    Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI

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    8th International Conference on Nuclear Physics at Storage Rings Stori11, October 9-14, 2011 Laboratori Nazionale di Frascati, Italy. Storage rings offer the possibility of measuring proton- and alpha-induced reactions in inverse kinematics. The combination of this approachwith a radioactive beamfacility allows, in principle, the determination of the respective cross sections for radioactive isotopes. Such data are highly desired for a better understanding of astrophysical nucleosynthesis processes like the p-process. A pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSI using a stable 96Ru beam at 9-11 AMeV and a hydrogen target. Monte-Carlo simulations of the experiment were made using the Geant4 code. In these simulations, the experimental setup is described in detail and all reaction channels can be investigated. Based on the Geant4 simulations, a prediction of the shape of different spectral components can be performed. A comparison of simulated predictions with the experimental results shows a good agreement and allows the extraction of the cross section

    Pulse shape analysis of signals from BaF2 and CeF3 scintillators for neutron capture experiments

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    The scope of this work is to study the characteristics of BaF2 and CeF3 signals using fast digitizers, which allow the sampling of the signal at very high frequencies and the application of the fitting method for analysis of the recorded pulses. By this procedure particle identification and the reconstruction of pile-up events can be improved, while maintaining the energy and time-of-flight resolution as compared to traditional methods. The reliability of the technique and problems connected with data acquisition are discussed with respect to accurate measurements of neutron capture cross-sections

    63Cu(n,ő≥)¬†cross section measured via 25 keV activation and time of flight

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    In the nuclear mass range A ‚Čą 60 to 90 of the solar abundance distribution the weak s-process component is the dominant contributor. In this scenario, which is related to massive stars, the overall neutron exposure is not sufficient for the s process to reach mass flow equilibrium. Hence, abundances and isotopic ratios are very sensitive to the neutron capture cross sections of single isotopes, and nucleosynthesis models need accurate experimental data. In this work we report on a new measurement of the 63Cu(n,ő≥ ) cross section for which the existing experimental data show large discrepancies. The 63Cu(n,ő≥ ) cross section at kBT = 25 keV was determined via activation with a quasistellar neutron spectrum at the Joint Research Centre (JRC) in Geel, and the energy dependence was determined with the time-of-flight technique and the calorimetric 4ŌÄ BaF2 detector array DANCE at the Los Alamos National Laboratory.We provide new cross section data for the whole astrophysically relevant energy range.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

    Coulomb dissociation of N 20,21

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    Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,ő≥)N20 and N20(n,ő≥)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,ő≥)N20 rate is up to a factor of 5 higher at

    Coulomb dissociation of O-16 into He-4 and C-12

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    We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4
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