The study of the resonant structures in neutron-nucleus cross-sections, and therefore of the compound-nucleus reaction mechanism, requires spectroscopic measurements to determine with high accuracy ...the energy of the neutron interacting with the material under study. To this purpose, the neutron time-of-flight facility n_TOF has been operating since 2001 at CERN. Its characteristics, such as the high intensity instantaneous neutron flux, the wide energy range from thermal to few GeV, and the very good energy resolution, are perfectly suited to perform high-quality measurements of neutron-induced reaction cross sections. The precise and accurate knowledge of these cross sections plays a fundamental role in nuclear technologies, nuclear astrophysics and nuclear physics. Two different measuring stations are available at the n_TOF facility, called EAR1 and EAR2, with different characteristics of intensity of the neutron flux and energy resolution. These experimental areas, combined with advanced detection systems lead to a great flexibility in performing challenging measurement of high precision and accuracy, and allow the investigation isotopes with very low cross sections, or available only in small quantities, or with very high specific activity. The characteristics and performances of the two experimental areas of the n_TOF facility will be presented, together with the most important measurements performed to date and their physics case. In addition, the significant upcoming measurements will be introduced.
The Cosmological Lithium Problem refers to the large discrepancy between the abundance of primordial 7Li predicted by the standard theory of Big Bang Nucleosynthesis and the value inferred from the ...so-called “Spite plateau” in halo stars. A possible explanation for this longstanding puzzle in Nuclear Astrophysics is related to the incorrect estimation of the destruction rate of 7Be, which is responsible for the production of 95% of primordial Lithium. While charged-particle induced reactions have mostly been ruled out, data on the 7Be(n,α) and 7Be(n,p) reactions are scarce or completely missing, so that a large uncertainty still affects the abundance of 7Li predicted by the standard theory of Big Bang Nucleosynthesis. Both reactions have been measured at the n_TOF facility at CERN, providing for the first time data in a wide neutron energy range.
We have used the 4π BaF2 gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n +87Sr by measuring the ...gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum ℓ to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.
The capture cross sections of 241Am and 243Am were measured at the n_TOF facility at CERN in the epithermal energy range with a BaF2 Total Absorption Calorimeter. A preliminary analysis of the 241Am ...and a complete analysis of the 243Am measurement, including the data reduction and the resonance analysis, have been performed.
The (n, α) reaction in the radioactive 59Ni is of relevance in nuclear astrophysics as 59Ni can be considered as the first branching point in the astrophysical s-process. Its relevance in nuclear ...technology is especially related to material embrittlement in stainless steel. However, there is a discrepancy between available experimental data and the evaluated nuclear data files for this reaction. At the n_TOF facility at CERN, a dedicated system based on sCVD diamond diodes was set up to measure the 59Ni(n, α)56Fe cross section. The results of this measurement, with special emphasis on the dominant resonance at 203 eV, are presented here.
The accurate knowledge of relevant nuclear data is crucial for the design of advanced nuclear systems. These data include neutron cross sections of various plutonium isotopes and other minor ...actinides. The 242Pu(n,f) cross section was measured at the CERN n_TOF facility, taking advantage of the wide energy range (from thermal to GeV) and the high instantaneous flux of the neutron beam. Preliminary results for the measurement are presented.
Current and future nuclear technologies require more accurate nuclear data on (n,γ) cross sections and the α-ratios of fissile isotopes. Their measurement presents several difficulties, mainly ...related to the strong fission γ-ray background competing with the weaker γ-ray cascades used as the experimental signature of the (n,γ) process. A specific setup was used at the CERN n_TOF facility in 2012 for the measurement of the (n,γ) cross section and α-ratios of fissile isotopes and used for the case of the 235U isotope. The setup consists of a set of micromegas fission detectors surrounding the 235U samples all placed inside a segmented BaF2 Total Absorption Calorimeter.
Neutron induced capture cross section on 236U has been measured with high accuracy and high resolution at n_TOF, in order to improve data libraries needed for the development of advanced nuclear ...reactors. Preliminary results obtained with two different detection systems are reported.
The 241Am(n,γ) cross sections have been measured at the n_TOF facility at CERN using C6D6 liquid scintillators and time of flight spectrometry. The results in the resolved resonance range bring new ...constraints to evaluations below 150 eV, and the energy upper limit can be extended from 150 eV to 320 eV. The analysis goes from thermal energy to 150 keV, and the unresolved resonance range cross section turns out to be larger than expected by evaluations or otherwise measured by previous works. The thermal cross section is found to be σth = 740 ± 74 barns, which is larger than expected by evaluations and most previous measurements.
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