370 research outputs found

    Neutron activation of natural zinc samples at kT = 25 keV

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    The neutron-capture cross sections of 64Zn, 68Zn, and 70Zn have been measured with the activation technique in a quasistellar neutron spectrum corresponding to a thermal energy of kT = 25 keV. By a series of repeated irradiations with different experimental conditions, an uncertainty of 3% could be achieved for the 64Zn(n,g)65Zn cross section and for the partial cross section 68Zn(n,g)69Zn-m feeding the isomeric state in 69Zn. For the partial cross sections 70Zn(n,g)71Zn-m and 70Zn(n,g)71Zn-g, which had not been measured so far, uncertainties of only 16% and 6% could be reached because of limited counting statistics and decay intensities. Compared to previous measurements on 64,68Zn, the uncertainties could be significantly improved, while the 70Zn cross section was found to be two times smaller than existing model calculations. From these results Maxwellian average cross sections were determined between 5 and 100 keV. Additionally, the beta-decay half-life of 71Zn-m could be determined with significantly improved accuracy. The consequences of these data have been studied by network calculations for convective core He burning and convective shell C burning in massive stars

    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

    Kabul Times (April 11, 1964, vol. 3, no. 37)

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    High-resolution photon scattering experiments have been performed on the nucleus 45Sc at the Darmstadt superconducting electron accelerator S-DALINAC using bremsstrahlung beams with end point energies of 5.0 and 7.0MeV. Energies, absolute cross-sections and decay widths of 50 states, most of them previously unknown, have been determined. The results are compared to (γ,γ \gamma{^\prime}) experiments on the neighbouring closed proton shell isotope 44Ca

    The s-process branching at 185W

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    The neutron capture cross section of the unstable nucleus 185W has been derived from experimental photoactivation data of the inverse reaction 186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the theoretically predicted neutron capture cross section of 185W of sigma = 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n = (3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching. In a stellar s-process model one finds a significant overproduction of the residual s-only nucleus 186Os.Comment: ApJ, in pres

    Predicted cross sections for photon-induced particle emission

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    Cross sections for the photon-induced particle-emission reactions (gamma,n), (gamma,p), and (gamma,alpha) are given for all natural isotopes from Ti to Bi. The target nuclei are assumed to be in their ground states, except for 180Ta which is naturally occurring as the isomer 180mTa. The cross sections are calculated in a statistical model (Hauser-Feshbach) approach and covering an energy range from threshold up to 7.35 MeV above the threshold (14.7 MeV above threshold for (gamma,alpha) reactions). The results are intended to aid conception and analysis of experiments which can also be used to test the methods involved in predicting astrophysical reaction rates for nucleosynthesis.Comment: 74 pages (including three long tables), accepted for publication in Atomic Data Nuclear Data Tables, corrected header of Table

    High precision 89^{89}Y(α\alpha,α\alpha)89^{89}Y scattering at low energies

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    Elastic scattering cross sections of the 89^{89}Y(α\alpha,α\alpha)89^{89}Y reaction have been measured at energies Ec.m._{c.m.} = 15.51 and 18.63 MeV. The high precision data for the semi-magic N=50N = 50 nucleus 89^{89}Y are used to derive a local potential and to evaluate the predictions of global and regional α\alpha-nucleus potentials. The variation of the elastic alpha scattering cross sections along the N=50N = 50 isotonic chain is investigated by a study of the ratios of angular distributions for 89^{89}Y(α\alpha,α\alpha)89^{89}Y and 92^{92}Mo(α\alpha,α\alpha)92^{92}Mo at Ec.m._{c.m.} \approx 15.51 and 18.63 MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, α\alpha-cluster states in 93^{93}Nb = 89^{89}Y \otimes α\alpha are investigated

    Cross-section measurement of the Ba 130 (p,γ) La 131 reaction for γ -process nucleosynthesis

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    Background: Deviations between experimental data of charged-particle-induced reactions and calculations within the statistical model are frequently found. An extended data base is needed to address the uncertainties regarding the nuclear-physics input parameters in order to understand the nucleosynthesis of the neutron-deficient p nuclei. Purpose: A measurement of total cross-section values of the Ba130(p,γ)La131 reaction at low proton energies allows a stringent test of statistical model predictions with different proton+nucleus optical model potentials. Since no experimental data are available for proton-capture reactions in this mass region around A ≈130, this measurement can be an important input to test the global applicability of proton+nucleus optical model potentials. Method: The total reaction cross-section values were measured by means of the activation method. After the irradiation with protons, the reaction yield was determined by use of γ-ray spectroscopy using two clover-type high-purity germanium detectors. In total, cross-section values for eight different proton energies could be determined in the energy range between 3.6 MeV ≤Ep≤ 5.0 MeV, thus, inside the astrophysically relevant energy region. Results: The measured cross-section values were compared to Hauser-Feshbach calculations using the statistical model codes TALYS and SMARAGD with different proton+nucleus optical model potentials. With the semimicroscopic JLM proton+nucleus optical model potential used in the SMARAGD code, the absolute cross-section values are reproduced well, but the energy dependence is too steep at the lowest energies. The best description is given by a TALYS calculation using the semimicroscopic Bauge proton+nucleus optical model potential using a constant renormalization factor. Conclusions: The statistical model calculation using the Bauge semimicroscopic proton+nucleus optical model potential deviates by a constant factor of 2.1 from the experimental data. Using this model, an experimentally supported stellar reaction rate for proton capture on the p nucleus Ba130 was calculated. At astrophysical temperatures, an increase in the stellar reaction rate of 68% compared to rates obtained from the widely used NON-SMOKER code is found. This measurement extends the scarce experimental data base for charged-particle-induced reactions, which can be helpful to derive a more globally applicable proton+nucleus optical model potential.Peer reviewedFinal Accepted Versio
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