Publications (60)28.14 Total impact
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Article: Experimental challenges for the Re/Os clock
Proceedings of the International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX. 25-30 June 2006, CERN. 04/2013; -1:55. -
Article: Neutron capture measurements on the s-process termination isotopes lead and bismuth
04/2013; -1:58. -
Article: Au(n,gamma) - the making of a new standard
Proceedings Of Science. Nuclear Astrophysics - Nuclei in the Cosmos IX. 04/2013; -1:80. -
Article: Measurement of the reaction O-17(\alpha,n)Ne-20 and its impact on the s process in massive stars
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ABSTRACT: The ratio between the rates of the reactions O-17(\alpha,n)Ne-20 and O-17(\alpha,\gamma)Ne-21 determines whether O-16 is an efficient neutron poison for the s process in massive stars, or if most of the neutrons captured by O-16(n,\gamma) are recycled into the stellar environment. This ratio is of particular relevance to constrain the s process yields of fast rotating massive stars at low metallicity. Recent results on the (\alpha,\gamma) channel have made it necessary to measure the (\alpha,n) reaction more precisely and investigate the effect of the new data on s process nucleosynthesis in massive stars. We present a new measurement of the O-17(\alpha, n) reaction using a moderating neutron detector. In addition, the (\alpha, n_1) channel has been measured independently by observation of the characteristic 1633 keV \gamma-transition in Ne-20. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. (\alpha,n) and (\alpha, \gamma) resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature. A new O-17(\alpha,n) reaction rate was deduced for the temperature range 0.1 GK to 10 GK. It was found that in He burning conditions the (\alpha,\gamma) channel is strong enough to compete with the neutron channel. This leads to a less efficient neutron recycling compared to a previous suggestion of a very weak (\alpha,\gamma) channel. S process calculations using our rates confirm that massive rotating stars do play a significant role in the production of elements up to Sr, but they strongly reduce the s process contribution to heavier elements.04/2013; -
Article: The $^93$Zr($n,$gamma$$) reaction up to 8 keV neutron energy
Phys. Rev. C. 01/2013; 87(1):014622. -
Article: Neutron-induced fission cross section of $^245$Cm: New results from data taken at the time-of-flight facility n$_$TOF
Phys. Rev. C. 03/2012; 85(3):034616. -
Article: Neutron-induced fission cross section measurement of U-233, Am-241 and Am-243 in the energy range 0.5 MeV <= E-n <= 20 MeV at n_TOF at CERN
Physica Scripta 01/2012; T150. · 1.20 Impact Factor -
Article: Neutron-induced fission cross section measurement of U-233, Am-241 and Am-243 in the energy range 0.5 MeV <= E-n <= 20 MeV at n_TOF at CERN
Physica Scripta 01/2012; T150. · 1.20 Impact Factor -
Article: A high energy-resolution zero degree facility for (p,p') and (p,t) reactions
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ABSTRACT: Medium-energy hadronic scattering and reactions at zero degrees are very selective to excitations with low angular momentum transfer. Only a few facilities exist worldwide where high energy-resolution measurements of this nature can be performed. The K600 Zero-Degree Facility at iThemba LABS, South Africa, was recently successfully developed. Measurements were performed for inelastic proton scattering at an incident energy of 200 MeV for targets ranging from 27Al to 208Pb. Excitation energy-resolution of 50 keV (FWHM) was achieved. A reasonable background subtraction procedure allows for the extraction of excitation energy spectra with low background. Measurements of the (p,t) reaction at 100 MeV benefit from a large difference in magnetic rigidity between the reaction products and primary particles, resulting in almost background-free spectra with excitation energy-resolution of 32 keV (FWHM).Journal of Physics Conference Series 09/2011; 312(5):052016. -
Article: First direct measurement of resonance strengths in 17O({\alpha}, {\gamma})21Ne
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ABSTRACT: The reaction 17O({\alpha},{\gamma})21Ne has been measured by in-beam gamma spectroscopy for the first time in the energy range E{\alpha} = 750 keV to 1650 keV using highly enriched anodized Ta2(17O)5 targets. Resonances were found at E({\alpha}) = 1002 keV, 1386 keV and 1619 keV. Their strengths and primary gamma-ray branchings are given. The new results exclude the low reaction rate of Descouvemont and support the rate of Caughlan and Fowler. Implications for the neutron poisoning efficiency of 16O in the weak s process are discussed.05/2011; -
Article: (197)Au(n,gamma) cross section in the unresolved resonance region
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ABSTRACT: The cross section of the reaction (197)Au(n,gamma) was measured with the time-of-flight technique at the n_TOF (neutron time-of-flight) facility in the unresolved resonance region between 5 and 400 keV using a pair of C(6)D(6) (where D denotes (2)H) liquid scintillators for the detection of prompt capture gamma rays. The results with a total uncertainty of 3.9%-6.7% for a resolution of 20 bins per energy decade show fair agreement with the Evaluated Nuclear Data File Version B-VII.0 (ENDF/B-VII.0), which contains the standard evaluation. The Maxwellian-averaged cross section (MACS) at 30 keV is in excellent agreement with the one according to the ENDF/B-VII.0 evaluation and 4.7% higher than the MACS measured independently by activation technique. Structures in the cross section, which had also been reported earlier, have been interpreted as being due to clusters of resonances.Physical Review C. 01/2011; 83(3). -
Article: (197)Au(n,gamma) cross section in the unresolved resonance region
Physical Review C. 01/2011; 83(3). -
Article: Constraining the S factor of 15N(p,g)16O at Astrophysical Energies
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ABSTRACT: The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338 <Ep < 1028 keV) can dramatically effect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation the 15N(p,g)16O reaction has been remeasured covering the energy range from Ep=1800 keV down to 130 keV. The results have been analyzed in the framework of a multi-level R-matrix theory and a S(0) value of 39.6 keV b has been found.11/2010; -
Article: $^197mathrmAu$($n,$gamma$$) cross section in the resonance region
Phys. Rev. C. 04/2010; 81(4):044616. -
Article: $^197mathrmAu$($n,$gamma$$) cross section in the resonance region
Phys. Rev. C. 04/2010; 81(4):044616. -
Article: High-accuracy 233U(n,f) cross-section measurement at the white-neutron source n_TOF from near-thermal to 1 MeV neutron energy
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ABSTRACT: The 233U(n,f) cross section has been measured at the white neutron source n_TOF in a wide energy range with a dedicated fission ionization chamber. We report here the results from ~30 meV to 1 MeV neutron energy. The 233U(n,f) cross section has been determined relative to a reference sample of 235U(n,f) measured simultaneously with the same detector. The very high instantaneous neutron flux and the intrinsically low background of the n_TOF installation result in an accuracy around 3% in the whole energy range, while the energy resolution of the neutron beam allows for an accurate description of the fission cross section by means of R-matrix analysis over a wide energy range. The results are, in general, in good agreement with the most recent high-accuracy measurement of this fission cross section, over the more limited range of the previous measurements, and indicated that even the latest evaluations underestimate the cross section in the epithermal region. The present high-quality data provide the basis for a more precise evaluation of the 233U fission cross section and for improving the reliability of databases needed for the design of new energy systems based on the Th/U cycle.Phys. Rev. C. 10/2009; 80(4). -
Article: The 14C(n,g) cross section between 10 keV and 1 MeV
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ABSTRACT: The neutron capture cross section of 14C is of relevance for several nucleosynthesis scenarios such as inhomogeneous Big Bang models, neutron induced CNO cycles, and neutrino driven wind models for the r process. The 14C(n,g) reaction is also important for the validation of the Coulomb dissociation method, where the (n,g) cross section can be indirectly obtained via the time-reversed process. So far, the example of 14C is the only case with neutrons where both, direct measurement and indirect Coulomb dissociation, have been applied. Unfortunately, the interpretation is obscured by discrepancies between several experiments and theory. Therefore, we report on new direct measurements of the 14C(n,g) reaction with neutron energies ranging from 20 to 800 keV.10/2009; -
Article: Fission cross-section measurements on 233U and minor actinides at the CERN n_TOF facility
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ABSTRACT: Neutron-induced fission cross-sections of minor actinides have been measured at the white neutron source n_TOF at CERN, Geneva. The studied isotopes include 233U, interesting for Th/U based nuclear fuel cycles, 241,243Am and 245Cm, relevant for transmutation and waste reduction studies in new generation fast reactors (Gen-IV) or Accelerator Driven Systems. The measurements take advantage of the unique features of the n_TOF facility, namely the wide energy range, the high instantaneous neutron flux and the low background. Results for the involved isotopes are reported from ~30 meV to around 1 MeV neutron enegy. The measurements have been performed with a dedicated Fission Ionization Chamber (FIC), relative to the standard cross-section of the 235U fission reaction, measured simultaneously with the same detector. Results are here reported.09/2009; 1175:211-218. -
Article: Measurements of proton induced reaction cross sections on 120Te for the astrophysical p-process
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ABSTRACT: The total cross sections for the 120Te(p,gamma)121I and 120Te(p,n)120I reactions have been measured by the activation method in the effective center-of-mass energies between 2.47 MeV and 7.93 MeV. The targets were prepared by evaporation of 99.4 % isotopically enriched 120Te on Aluminum and Carbon backing foils, and bombarded with proton beams provided by the FN tandem accelerator at the University of Notre Dame. The cross sections and $S$ factors were deduced from the observed gamma ray activity, which was detected off-line by two Clover HPGe detectors mounted in close geometry. The results are presented and compared with the predictions of statistical model calculations using the codes NON-SMOKER and TALYS. Comment: 17 pages, 5 figures, 5 tables, regular article08/2009; -
Article: The reactions {sup 25}Mg({alpha},n){sup 28}Si, {sup 26}Mg({alpha},n){sup 29}Si and their possible impact on nucleosynthesis
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ABSTRACT: At the time neon burning is activated in massive stars, large amounts of {sup 25}Mg and {sup 26}Mg have been accumulated from the previous evolutionary phases. In particular, at typical temperatures for neon shell burning, the reactions {sup 25}Mg({alpha},n){sup 28}Si and {sup 26}Mg({alpha},n){sup 29}Si become efficient providing additional neutron fluxes and affecting the nucleosynthesis distribution. Good knowledge of the reaction rates is required to study their effect on nucleosynthesis during neon shell burning conditions (T{sub 9} > or approx. 1.5, where T{sub 9} is the temperature in gigakelvin). At the Nuclear Science Laboratory, University of Notre Dame, IN, USA we developed a neutron detector to investigate the {sup 25}Mg({alpha},n){sup 28}Si and {sup 26}Mg({alpha},n){sup 29}Si reactions as possible neutron sources during neon shell burning. In the present paper we briefly describe the experimental procedures developed to measure those reactions. Finally, we discuss the impact of {sup 25}Mg({alpha},n){sup 28}Si and {sup 26}Mg({alpha},n){sup 29}Si on the s-process nucleosynthesis for the barium isotopes.AIP Conference Proceedings 01/2009; 1090(1).
Top co-authors
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Institutions
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2006–2011
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University of Notre Dame
- Department of Physics
Indiana, PA, USA
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2004
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INFN - Istituto Nazionale di Fisica Nucleare
Frascati, Latium, Italy
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