0000000000208177
AUTHOR
J. A. Ryan
New measurement of the 242Pu(n,γ) cross section at n-TOF-EAR1 for MOX fuels: Preliminary results in the RRR
The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with 238U to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. The use of MOX fuels in thermal and fast reactors requires accurate capture and fission cross sections. For the particular case of 242Pu, the previous neutron capture cross section measurements were made in the 70’s, providing an uncertainty of about 35% in the keV region. In this context, the Nuclear Energy Agency recommends in its “High Priority Request List” and its report WPEC-26 that the capture cross section of 242Pu…
7Be(n,α) and 7Be(n,p) cross-section measurement for the cosmological lithium problem at the n-TOF facility at CERN
One of the most puzzling problems in Nuclear Astrophysics is the “Cosmological Lithium Problem”, i.e the discrepancy between the primordial abundance of \(^{7}\)Li observed in metal poor halo stars (Asplund et al. in Astrophys J 644:229–259, 2006, [1]), and the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact on the problem is \(^{7}\)Be(n,p)\(^{7}\)Li. Despite of the importance of this reaction in BBN, the cross-section has never been directly measured at the energies of interest for BBN. Taking advantage of the innovative features of the second experimental area at the n\(\_\)TOF facility at CERN (Sabate-Gilarte et al. in Eur Phys J A 53:210,…
The n_TOF facility: Neutron beams for challenging future measurements at CERN
The CERN n TOF neutron beam facility is characterized by a very high instantaneous neutron flux, excellent TOF resolution at the 185 m long flight path (EAR-1), low intrinsic background and coverage of a wide range of neutron energies, from thermal to a few GeV. These characteristics provide a unique possibility to perform high-accuracy measurements of neutron-induced reaction cross-sections and angular distributions of interest for fundamental and applied Nuclear Physics. Since 2001, the n TOF Collaboration has collected a wealth of high quality nuclear data relevant for nuclear astrophysics, nuclear reactor technology, nuclear medicine, etc. The overall efficiency of the experimental prog…
Be7(n,α)He4Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN
The energy-dependent cross section of the (7)Bed(n,alpha)He-4 reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of Be-7 and by the low reaction cross section have been overcome at n_TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n_TOF facility at CERN, the availability of a sufficient amount of chemically pure Be-7, and a specifically designed experimental setup. Coincidences between the two alpha particles have been…
The Nuclear astrophysics program at n_TOF (CERN)
An important experimental program on Nuclear Astrophysics is being carried out at the n_TOF since several years, in order to address the still open issues in stellar and primordial nucleosynthesis. Several neutron capture reactions relevant to s-process nucleosynthesis have been measured so far, some of which on important branching point radioisotopes. Furthermore, the construction of a second experimental area has recently opened the way to challenging measurements of (n, charged particle) reactions on isotopes of short half-life. The Nuclear Astrophysics program of the n_TOF Collaboration is here described, with emphasis on recent results relevant for stellar nucleosynthesis, stellar neut…
The 33S(n,α)30Si cross section measurement at n TOF-EAR2 (CERN): From 0.01 eV to the resonance region
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).
Measurement of the Pu-242(n,gamma) cross section from thermal to 500 keV at the Budapest research reactor and CERN n_TOF-EAR1 facilities
The design and operation of innovative nuclear systems requires a better knowledge of the capture and fission cross sections of the Pu isotopes. For the case of capture on 242Pu, a reduction of the uncertainty in the fast region down to 8-12% is required. Moreover, aiming at improving the evaluation of the fast energy range in terms of average parameters, the OECD NEA High Priority Request List (HPRL) requests high-resolution capture measurements with improved accuracy below 2 keV. The current uncertainties also affect the thermal point, where previous experiments deviate from each other by 20%. A fruitful collaboration betwen JGU Mainz and HZ Dresden-Rossendorf within the EC CHANDA project…
The 236U neutron capture cross-section measured at the n TOF CERN facility
International audience; The $^{236}$U isotope plays an important role in nuclear systems, both for future and currently operating ones. The actual knowledge of the capture reaction of this isotope is satisfactory in the thermal region, but it is considered insufficient for Fast Reactor and ADS applications. For this reason the $^{236} \text{U}(n, \gamma)$ reaction cross-section has been measured for the first time in the whole energy region from thermal energy up to 1 MeV at the n_TOF facility with two different detection systems: an array of C$_6$D$_6$ detectors, employing the total energy deposited method, and a 4$\pi$ total absorption calorimeter (TAC), made of 40 BaF$_2$ crystals. The t…
High precision measurement of the radiative capture cross section of 238U at the n_TOF CERN facility
The importance of improving the accuracy on the capture cross-section of 238U has been addressed by the Nuclear Energy Agency, since its uncertainty significantly affects the uncertainties of key design parameters for both fast and thermal nuclear reactors. Within the 7th framework programme ANDES of the European Commission three different measurements have been carried out with the aim of providing the 238U(n,γ) cross-section with an accuracy which varies from 1 to 5%, depending on the energy range. Hereby the final results of the measurement performed at the n-TOF CERN facility in a wide energy range from 1 eV to 700 keV will be presented. © The Authors, published by EDP Sciences, 2017.
Radiative neutron capture on Pu242 in the resonance region at the CERN n_TOF-EAR1 facility
The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with uranium to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. However, an extensive use of MOX fuels, in particular in fast reactors, requires more accurate capture and fission cross sections for some Pu isotopes. In the case of Pu242 there are sizable discrepancies among the existing capture cross-section measurements included in the evaluations (all from the 1970s) resulting in an uncertainty as high as 35% in the fast energy region. Moreover, postirradiation experiments evaluat…
The measurement programme at the neutron time-of-flight facility n_TOF at CERN
Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN’s neutron time-of-flight facility n TOF has produced a considerabl…
Measurement of the 241Am neutron capture cross section at the n-TOF facility at CERN
New neutron cross section measurements of minor actinides have been performed recently in order to reduce the uncertainties in the evaluated data, which is important for the design of advanced nuclear reactors and, in particular, for determining their performance in the transmutation of nuclear waste. We have measured the 241 Am(n,γ) cross section at the n TOF facility between 0.2 eV and 10 keV with a BaF2 Total Absorption Calorimeter, and the analysis of the measurement has been recently concluded. Our results are in reasonable agreement below 20 eV with the ones published by C. Lampoudis et al. in 2013, who reported a 22% larger capture cross section up to 110 eV compared to experimental …
Nuclear data activities at the n_TOF facility at CERN
International audience; Nuclear data in general, and neutron-induced reaction cross sections in particular, are important for a wide variety of research fields. They play a key role in the safety and criticality assessment of nuclear technology, not only for existing power reactors but also for radiation dosimetry, medical applications, the transmutation of nuclear waste, accelerator-driven systems, fuel cycle investigations and future reactor systems as in Generation IV. Applications of nuclear data are also related to research fields as the study of nuclear level densities and stellar nucleosynthesis. Simulations and calculations of nuclear technology applications largely rely on evaluate…
The MEGA project
Abstract We describe the development of a new telescope for Medium Energy Gamma-Ray Astronomy (MEGA) for the energy band 0.4–50 MeV. As a successor to COMPTEL and EGRET (low energies), MEGA aims to improve the sensitivity for astronomical sources by at least an order of magnitude. It could thus fill the severe sensitivity gap between scheduled or operating hard-X-ray and high-energy γ-ray missions and open the way for a future Advanced Compton Telescope. MEGA records and images γ-rays by completely tracking Compton and Pair creation events in a stack of double sided Si-strip track detectors surrounded by a pixelated CsI calorimeter. A scaled down prototype has been built and calibrations us…