215 research outputs found
Measurements of neutron-induced reactions in inverse kinematics and applications to nuclear astrophysics
Neutron capture cross sections of unstable isotopes are important for
neutron-induced nucleosynthesis as well as for technological applications. A
combination of a radioactive beam facility, an ion storage ring and a high flux
reactor would allow a direct measurement of neutron induced reactions over a
wide energy range on isotopes with half lives down to minutes. The idea is to
measure neutron-induced reactions on radioactive ions in inverse kinematics.
This means, the radioactive ions will pass through a neutron target. In order
to efficiently use the rare nuclides as well as to enhance the luminosity, the
exotic nuclides can be stored in an ion storage ring. The neutron target can be
the core of a research reactor, where one of the central fuel elements is
replaced by the evacuated beam pipe of the storage ring. Using particle
detectors and Schottky spectroscopy, most of the important neutron-induced
reactions, such as (n,), (n,p), (n,), (n,2n), or (n,f), could
be investigated.Comment: 5 pages, 7 figures, Invited Talk given at the Fifteenth International
Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15),
Dresden, Germany, 201
Neutron capture cross sections of 69Ga and 71Ga at 25 keV and e peak = 90 keV
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 γ emission of the product nuclei by high-purity germanium detectors. We present preliminary results.publishersversionpublishe
The Ni(n,) cross section measured with DANCE
The neutron capture cross section of the s-process branch nucleus Ni
affects the abundances of other nuclei in its region, especially Cu and
Zn. In order to determine the energy dependent neutron capture cross
section in the astrophysical energy region, an experiment at the Los Alamos
National Laboratory has been performed using the calorimetric 4 BaF
array DANCE. The (n,) cross section of Ni has been determined
relative to the well known Au standard with uncertainties below 15%.
Various Ni resonances have been identified based on the Q-value.
Furthermore, the s-process sensitivity of the new values was analyzed with the
new network calculation tool NETZ.Comment: 11 pages, 13 page
Neutron activation of Ga and Ga at kBT≈25 keV
Background: About 50% of heavy elements are produced by the slow neutron capture process (s process) in stars. The element gallium is mostly produced during the weak s process in massive stars.
Purpose: Our activation at kT≈25 keV is the first experiment in a series of activation and time-of-flight measurements on Ga and Ga relevant for astrophysics.
Methods: We activated Ga and Ga with a neutron distribution that corresponds to a quasistellar distribution with kT=25 keV at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction Li(p,n). The produced activity was measured via the γ emission by the decaying product nuclei by high-purity germanium detectors.
Results: We provide spectrum-averaged cross sections (SACS) and ratios of the cross sections σ/σ for the neutron spectrum of the activation. We obtain values of σ=(186±12) mb and σ = (112±7) mb, and cross section ratios of σ/σ=0.29±0.02 and σ/σ = 0.17±0.01.
Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for Ga and about 20% lower for Ga
Thermal neutron capture cross section of the radioactive isotope Fe 60
Background: Fifty percent of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections. Purpose: One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as Fe60 with a half-life of 2.60×106 yr. To reproduce this γ activity in the universe, the nucleosynthesis of Fe60 has to be understood reliably. Methods: An Fe60 sample produced at the Paul Scherrer Institut (Villigen, Switzerland) was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-Universität Mainz (Mainz, Germany). Results: The thermal neutron capture cross section has been measured for the first time to σth=0.226(-0.049+0.044)b. An upper limit of σRI<0.50b could be determined for the resonance integral. Conclusions: An extrapolation towards the astrophysically interesting energy regime between kT=10 and 100 keV illustrates that the s-wave part of the direct capture component can be neglected
Nuclear astrophysics with radioactive ions at FAIR
The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes
Thermal (n, γ) cross section and resonance integral of 171Tm
Background: About 50% of the heavy elements are produced in stars during the slow neutron capture process.
The analysis of branching points allows us to set constraints on the temperature and the neutron density in the
interior of stars.
Purpose: The temperature dependence of the branch point 171Tm is weak. Hence, the 171Tm neutron capture
cross section can be used to constrain the neutron density during the main component of the s process in thermally
pulsing asymptotic giant branch (TP-AGB) stars.
Methods: A 171Tm sample produced at the ILL was activated with thermal and epithermal neutrons at the
TRIGA research reactor at the Johannes Gutenberg-Universität Mainz.
Results: The thermal neutron capture cross section and the resonance integral have been measured for the first
time to be σth = 9.9 ± 0.9 b and σRI = 193 ± 14 b.
Conclusions: Based on our results, new estimations of the direct capture components’ impact on the
Maxwellian-nAveraged cross sections (MACS) are possible.European Unions’s Seventh Framework Programme (FP/2007-2013
Ta(n, γ) cross-section measurement and the astrophysical origin of the Ta isotope
Ta is nature\u27s rarest (quasi) stable isotope and its astrophysical origin is an open question. A possible production site of this isotope is the slow neutron capture process in asymptotic giant branch stars, where it can be produced via neutron capture reactions on unstable Ta. We report a new measurement of the Ta(n,γ) Ta cross section at thermal-neutron energies via the activation technique. Our results for the thermal and resonance-integral cross sections are 952±57 and 2013±148 b, respectively. The thermal cross section is in good agreement with the only previous measurement [Phys. Rev. C 60, 025802 (1999)], while the resonance integral is different by a factor of ≈1.7. While neutron energies in this work are smaller than the energies in a stellar environment, our results may lead to improvements in theoretical predictions of the stellar cross section
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