409 research outputs found

    Total and partial cross sections of the 112^{112}Sn(α,γ\alpha,\gamma)116^{116}Te reaction measured via in-beam γ\gamma-ray spectroscopy

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    An extended database of experimental data is needed to address uncertainties of the nuclear-physics input parameters for Hauser-Feshbach calculations. Especially α\alpha+nucleus optical model potentials at low energies are not well known. The in-beam technique with an array of high-purity germanium (HPGe) detectors was successfully applied to the measurement of absolute cross sections of an (α\alpha,γ\gamma) reaction on a heavy nucleus at sub-Coulomb energies. The total and partial cross-section values were measured by means of in-beam γ\gamma-ray spectroscopy. Total and partial cross sections were measured at four different α\alpha-particle energies from Eα=10.5E_\alpha = 10.5 MeV to Eα=12E_\alpha = 12 MeV. The measured total cross-section values are in excellent agreement with previous results obtained with the activation technique, which proves the validity of the applied method. The experimental data was compared to Hauser-Feshbach calculations using the nuclear reaction code TALYS. A modified version of the semi-microscopic α\alpha+nucleus optical model potential OMP 3, as well as modified proton and γ\gamma widths, are needed in order to obtain a good agreement between experimental data and theory. It is found, that a model using a local modification of the nuclear-physics input parameters simultaneously reproduces total cross sections of the 112^{112}Sn(α\alpha,γ\gamma) and 112^{112}Sn(α\alpha,p) reactions. The measurement of partial cross sections turns out to be very important in this case in order to apply the correct γ\gamma-ray strength function in the Hauser-Feshbach calculations. The model also reproduces cross-section values of α\alpha-induced reactions on 106^{106}Cd, as well as of (α\alpha,n) reactions on 115,116^{115,116}Sn, hinting at a more global character of the obtained nuclear-physics input.Comment: 8 pages, 9 figure

    Experimental constraints on the γ\gamma-ray strength function in 90^{90}Zr using partial cross sections of the 89^{89}Y(p,γ\gamma)90^{90}Zr reaction

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    Partial cross sections of the 89^{89}Y(p,γ\gamma)90^{90}Zr reaction have been measured to investigate the γ\gamma-ray strength function in the neutron-magic nucleus 90^{90}Zr. For five proton energies between Ep=3.65E_p=3.65 MeV and Ep=4.70E_p=4.70 MeV, partial cross sections for the population of seven discrete states in 90^{90}Zr have been determined by means of in-beam γ\gamma-ray spectroscopy. Since these γ\gamma-ray transitions are dominantly of E1E1 character, the present measurement allows an access to the low-lying dipole strength in 90^{90}Zr. A γ\gamma-ray strength function based on the experimental data could be extracted, which is used to describe the total and partial cross sections of this reaction by Hauser-Feshbach calculations successfully. Significant differences with respect to previously measured strength functions from photoabsorption data point towards deviations from the Brink-Axel hypothesis relating the photo-excitation and de-excitation strength functions.Comment: 5 pages, 5 figure

    Symmetries at and Near Critical Points of Quantum Phase Transitions in Nuclei

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    We examine several types of symmetries which are relevant to quantum phase transitions in nuclei. These include: critical-point, quasidynamical, and partial dynamical symmetries.Comment: 5 pages, 4 figures, Proc. 13th Int. Conf. on "Capture Gamma-Ray Spectroscopy and Related Topics", August 25-29, 2008, Cologne, German

    A method to correct differential nonlinearities in subranging analog-to-digital converters used for digital gamma-ray spectroscopy

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    The influence on γ\gamma-ray spectra of differential nonlinearities (DNL) in subranging, pipelined analog-to-digital converts (ADCs) used for digital γ\gamma-ray spectroscopy was investigated. The influence of the DNL error on the γ\gamma-ray spectra, depending on the input count-rate and the dynamic range has been investigated systematically. It turned out, that the DNL becomes more significant in γ\gamma-ray spectra with larger dynamic range of the spectroscopy system. An event-by-event offline correction algorithm was developed and tested extensively. This correction algorithm works especially well for high dynamic ranges

    Lifetime measurement of excited low-spin states via the (p,pγ(p,p^{\prime}\gamma) reaction

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    In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96^{96}Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ\gamma-rays as well as the large number of particle and γ\gamma-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n,nγ(n,n^{\prime}\gamma) or - in case of investigating dipole excitations - (γ,γ\gamma,\gamma^{\prime}) experiments are not feasible due to the lack of sufficient isotopically enriched target material

    Elastic alpha-scattering of 112Sn and 124Sn at astrophysically relevant energies

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    The cross sections for the elastic scattering reactions {112,124}Sn(a,a){112,124}Sn at energies above and below the Coulomb barrier are presented and compared to predictions for global alpha-nucleus potentials. The high precision of the new data allows a study of the global alpha-nucleus potentials at both the proton and neutron-rich sides of an isotopic chain. In addition, local alpha-nucleus potentials have been extracted for both nuclei, and used to reproduce elastic scattering data at higher energies. Predictions from the capture cross section of the reaction 112Sn(a,g)116Te at astrophysically relevant energies are presented and compared to experimental data.Comment: 20 pages, 10 figures, accepted for publication in Phys. Rev.

    187^{187}Re(\gamm,n) cross section close to and above the neutron threshold

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    The neutron capture cross section of the unstable nucleus 186^{186}Re is studied by investigating the inverse photodisintegration reaction 187^{187}Re(γ\gamma,n). The special interest of the {\it s}-process branching point 186^{186}Re is related to the question of possible {\it s}-process contributions to the abundance of the {\it r}-process chronometer nucleus ^{187}Re.Weusethephotoactivationtechniquetomeasurephotodisintegrationrates.Ourexperimentalresultsareingoodagreementwithtwodifferentstatisticalmodelcalculations.AlthoughthecrosssectionspredictedbybothmodelsfortheinversereactionRe. We use the photoactivation technique to measure photodisintegration rates. Our experimental results are in good agreement with two different statistical model calculations. Although the cross sections predicted by both models for the inverse reaction ^{186}Re(n,Re(n,\gamma)istoolowtoremovetheoverproductionof) is too low to remove the overproduction of ^{186}$Os; the two predicted neutron-capture cross sections differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres

    How important is the Family? : Alpha nuclear potentials and p-process nucleosynthesis

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    Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike LicenceIn this work we present the results from the analysis of the experimentally measured angular distributions of the reaction 106Cd(α , α )106 Cd at several different energies around the Coulomb barrier. The difficulties that arise in the study of 106Cd-α -nuclear potential and the so called Family Problem are addressed in this work

    Q-phonon description of low lying 1^- two-phonon states in spherical nuclei

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    The properties of 1^-_1 two-phonon states and the characteristics of E1 transition probabilities between low-lying collective states in spherical nuclei are analysed within the Q-phonon approach to the description of collective states. Several relations between observables are obtained. Microscopic calculations of the E1 0^+_1 -> 1^-_1 transition matrix elements are performed on the basis of the RPA. A satisfactory description of the experimental data is obtained.Comment: 16 pages, 2 figures, 9 table
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