The accurate knowledge of the neutron-induced fission cross-sections of actinides and other isotopes involved in the nuclear fuel cycle is essential for the design of advanced nuclear systems, such ...as Generation-IV nuclear reactors. Such experimental data can also provide the necessary feedback for the adjustment of nuclear model parameters used in the evaluation process, resulting in the further development of nuclear fission models. In the present work, the 240Pu(n,f) cross-section was measured at CERN's n_TOF facility relative to the well-known 235U(n,f) cross section, over a wide range of neutron energies, from meV to almost MeV, using the time-of-flight technique and a set-up based on Micromegas detectors. This measurement was the first experiment to be performed at n_TOF's new experimental area (EAR-2), which offers a significantly higher neutron flux compared to the already existing experimental area (EAR-1). Preliminary results as well as the experimental procedure, including a description of the facility and the data handling and analysis, are presented.
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.
The 33S(n,α)30Si cross section measurement, using 10B(n,α) as reference, at the n_TOF Experimental Area 2 (EAR2) facility at CERN is presented. Data from 0.01 eV to 100 keV are provided and, for the ...first time, the cross section is measured in the range from 0.01 eV to 10 keV. These data may be used for a future evaluation of the cross section because present evaluations exhibit large discrepancies. The 33S(n,α)30Si reaction is of interest in medical physics because of its possible use as a cooperative target to boron in Neutron Capture Therapy (NCT).
We report on the measurement of the \(^{7}\)Be(\(n, p\))\(^{7}\)Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF ...facility at CERN. This reaction plays a key role in the lithium yield of the Big Bang Nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and showed a large discrepancy between each other. The measurement was performed with a Si-telescope, and a high-purity sample produced by implantation of a \(^{7}\)Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low-energy, relative to current evaluations, in the region of BBN interest the present results are consistent with the values inferred from the time-reversal \(^{7}\)Li(\(p, n\))\(^{7}\)Be reaction, thus yielding only a relatively minor improvement on the so-called Cosmological Lithium Problem (CLiP). The relevance of these results on the near-threshold neutron production in the p+\(^{7}\)Li reaction is also discussed.
We report on the measurement of the \(^{7}\)Be(\(n, p\))\(^{7}\)Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the ...n\_TOF facility at CERN. This reaction plays a key role in the lithium yield of the Big Bang Nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and showed a large discrepancy between each other. The measurement was performed with a Si-telescope, and a high-purity sample produced by implantation of a \(^{7}\)Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low-energy, relative to current evaluations, in the region of BBN interest the present results are consistent with the values inferred from the time-reversal \(^{7}\)Li(\(p, n\))\(^{7}\)Be reaction, thus yielding only a relatively minor improvement on the so-called Cosmological Lithium Problem (CLiP). The relevance of these results on the near-threshold neutron production in the p+\(^{7}\)Li reaction is also discussed.
The newly built second experimental area EAR2 of the n_TOF spallation neutron source at CERN allows to perform (n, charged particles) experiments on short-lived highly radioactive targets. This paper ...describes a detection apparatus and the experimental procedure for the determination of the cross-section of the 7Be(n,{\alpha}) reaction, which represents one of the focal points toward the solution of the cosmological Lithium abundance problem, and whose only measurement, at thermal energy, dates back to 1963. The apparently unsurmountable experimental difficulties stemming from the huge 7Be {\gamma}-activity, along with the lack of a suitable neutron beam facility, had so far prevented further measurements. The detection system is subject to considerable radiation damage, but is capable of disentangling the rare reaction signals from the very high background. This newly developed setup could likely be useful also to study other challenging reactions requiring the detectors to be installed directly in the neutron beam.
This book constitutes the refereed proceedings of the 34th Symposium of the German Association for Pattern Recognition, DAGM 2012, and the 36th Symposium of the Austrian Association for Pattern ...Recognition, OAGM 2012, held in Graz, Austria, in August 2012. The 27 revised full papers and 23 revised poster papers were carefully reviewed and selected from 98 submissions. The papers are organized in topical sections on segmentation, low-level vision, 3D reconstruction, recognition, applications, learning, and features.