1,721,450 research outputs found
Improvement of the Fission Channel in the EMPIRE Code
No full textThe new fission formalism implemented in EMPIRE-2.19 is presented along with several examples of applications to neutron- and photon-induced fission
Measurements at n_TOF ofthe Neutron Capture Cross Section of Minor Actinides Relevant to the Nuclear Waste Transmutation
No full textAccurate and reliable neutron-capture cross-section data far actinides are necessary for the proper design, safety regulation, and precise performance assessment of transmutation devices such as Fast Critical Reactors or Accelerator Driven Systems. In particular, the neutron-capture cross sections of 237Np, 240Pu, and 243Am play a key role in the design and optimization of a strategy far the Nuclear Waste Transmutation. The listed cross sections have been measured in 2004 at n_TOF with a high accuracy due to a combination of features unique in the world: high instantaneous neutron fluence and excellent energy resolution of the n_TOF facility, innovative Data Acquisition System based on flash ADCs, and the use of a high-performance BaF2 Total Absorption Calorimeter as a detection device
The n_TOF Facility at CERN: Performances and First Physics Results
No full textThe neutron Time of Flight (n_TOF) facility at CERN is a source of a wide-range (1 eV&lEn&l250 MeV) flux of neutrons, generated by spallation of 20-GeV/c protons onto a solid lead target. The goal of the n_TOF is to provide unprecedented precision in neutron kinetic energy determination, which will in turn bring the much-needed precision in neutron-induced cross-section measurements.The unique features of the n_TOF facility (instantaneously very intense neutron flux, low duty cycle, high resolution, and low background) make possible the measurement of highly radioactive isotopes usually available in small quantities. Such measurements are vital for a range of studies in fields as diverse as nuclear technology, astrophysics, and fundamental nuclear physics.In this paper, the characteristics of the n_TOF facility will be described, together with the main features of the high performance detectors and acquisition system used for cross-section measurements, with a summary of the results and experience acquired during the first years of operation
High-Resolution Study of 237Np Fission Cross Section from 5 eV to 1 MeV
No full textA series of measurements of 237Np fission cross section have been performed at the CERN spallation neutron facility n_TOF which covers a wide energy range from l eV up to 250 MeV. A fast ionization chamber (FIC) was used as a fission fragment detector with registration efficiency of not less than 97%. Particular attention was paid to correct the fission cross section with use of 235U standard. Total experimental uncertainties are determined to be at the level of 3%. Analysis of the experimental data in the restricted neutron energy from 5 eV up to 1 MeV showed a systematic deviation from evaluated data (ENDF/B- VI). This discrepancy amounts to up to a factor 3 for resolved resonances in the neutron energy range of 5 eV - 2 KeV, and is in good agreement with some previous experiments. A similar disagreement at the level of 6-7% was found for higher energies around the threshold (En = 300 keV-1 MeV). This energy range is essential for the transmutation of neptunium in ADS or fast reactors. Il is concluded that an updated evaluation of nuclear data for 237Np is required
Quantum Monte Carlo Study of Pairing Interaction of the Neutron-Ric A â 100 Nuclei
No full textThe experimental bandhead excitation energies of two-quasi-neutron rotational bands in 100Zr and 102Zr nuclei have been used in the frame of the quantum Monte Carlo(QMC) pairing model to determine the strength G of the neutron pairing interaction. Using this strength, the bandhead excitation energies of two-quasi-neutron rotational bands in 98Sr and 100Sr have been predicted. Effects of the particle number fluctuation, introduced by the Bardeen-Cooper-Schrieffer approximation, and absent in the QMC approach, are discussed. Shapes and ground state properties of nuclei from the neutron-rich zirconium and strontium isotopes are calculated using the macroscopic-microscopic method with the universal Woods-Saxon average potential and a monopole pairing residual interaction to obtain single-particle schemes relevant for pairing calculation. Our calculations are in good agreement with the experimental ground state deformation
Neutron Capture Cross Sections for the Re/Os Clock
No full textThe radioactive decay of 187Re 1870s (tl/2 = 43 Gyr) is suited for dating the onset of heavy-element nucleosynthesis. The radiogenic contribution to the 1870s abundance is the difference between the natural abundance and the corresponding s-process component. This component can be obtained via the well-established sigmaN systematics using the neighboring s-only isotope 186Os, provided the neutron-capture cross sections of both isotopes are known with sufficient accuracy. We report on a new set of experiments perforrned with a C6D6 detector array at the n_TOF neutron spallation facility of CERN. The capture cross sections of 1860s, 1870s, and 1880s have been measured in the neutron-energy range between1 eV and 1 MeV, and Maxwellian-averaged cross sections were deduced for the relevant thermal energies frolli kT=5 keV to 100kev
Measurement or the 232Th Neutron Capture Cross Section at the CERN n_TOF Facility
No full textThe use of a fuel cycle based on 232Th can substantially reduce the radiotoxicity of the produced nuclear waste since the lower atomic and mass number of thorium results in a strongly suppressed build-up of the higher actinides and especially americium and curium. The design and realization of nuclear power stations based on the use of thorium, either ina critical or subcritical system, require an accurate knowledge of the 232Th(n,gamma) reaction cross section. We have measured the neutron capture cross section of 232Th at the recently constructed neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. In the resolved resonance region, the resonance parameters have been extracted. In the unresolved resonance region, the neutron capture cross section is given as point-wise data
New Measurement of the Capture Cross Section of Bismuth and Lead Isotopes
No full textAll the stable lead isotopes and 209Bi bave been recently measured at n_TOF (CERN) in the range rom 1 eV up to 1 MeV, using an optimized experimental setup. A set of two homemade C6D6 detectors with carbon-fibre canning was designed to greatly reduce the sensitivity to scattered neutrons. Surrounding elements like the sample holder and the sample exchanger have been made also of carbon fibre.The pulse-height weighting technique has been used in order to determine the (n,gamma) cross sections. Concerning this technique, special care has been taken in the treatment of several sources of error leading to a total systematic uncertainty of less than 3%.Results on the analysed 209Bi and 207Pb capture data and a comparison with previous experiments and evaluations are presented
Shape Transitions in the Interacting Boson Model at Finite Temperature
No full textWe provide evidence for transition from a deformed equilibrium shape to a spherical equilibrium shape in the interacting boson model at finite temperature. The critical temperature strongly depends on the model used in estimating the effective boson number as a function of T
Recent Developments of the Nuclear Reaction Model Code EMPIRE
No full textRecent extensions and improvements of the EMPIRE code system are outlined. They add to the code new capabilities such as fission of actinides, preequilibrium emission of clusters, photo-nuclear reactions, and reactions on excited targets. These features, along with improved ENDF formatting, exclusive spectra, and recoils make the forthcoming 2.19 release a complete tool for evaluation of nuclear data at incident energies above the resonance region
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