• Energy Research

We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to Reviews of Modern Physics 70 (1998) 1265. 54 pages, 20 figures, version to be published in Reviews of Modern Physics; various typos corrected and several updates made

Nuclear data are fundamental quantities for developing nuclear energy concepts and research. They are essential for the simulation of nuclear systems, safety and performance calculations, and reactor instrumentation. Nuclear data improvement requires a combination of many different know-hows that are distributed over many institutions along Europe. In the EURATOM call for Nuclear Fission and Radiation Protection NFRP-2018, two nuclear data projects were started in September 2019: the Coordination and Support Action ARIEL (Accelerator and Research reactor Infrastructures for Education and Learning) and the Research and Innovation Action SANDA (Solving Challenges in Nuclear Data for the Safety of European Nuclear facilities). The ARIEL project integrates education and training of young scientists and technicians with access to neutron beam research infrastructures and supports scientific visits to conduct short-term research projects relevant to thesis works. The SANDA project is focuses on research innovation actions, including detector and nuclear target development, important nuclear data measurements, nuclear data evaluation, and validation. A description of these ongoing projects, including the first results, is the subject of this article.

Abstract The radiation source ELBE ( E lectron L inear accelerator with high B rilliance and low E mittance) at Forschungszentrum Dresden-Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to I e - = 1 mA at energies up to E e - = 40 MeV can be delivered with a pulse width of less than 10 ps. With these parameters the electron beam allows to generate sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and producing neutrons by bremsstrahlung photons through (γ, n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n, γ), (n, n′γ), (n, p), (n, α), and (n, f) at a time-of-flight arrangement with a short flight path of only a few meters it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons, which would broaden the neutron pulses. It is the primary physics objective of this neutron source to measure neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select materials with low activation cross sections, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. Furthermore experiments can be performed which address problems of nuclear astrophysics. The power deposition of the electron beam in the small neutron radiator volume of 1 cm 3 reaches up to 25 kW. This is such a high power density that any solid high Z number material would melt. Therefore, the neutron radiator consists of liquid lead circulated by an electromagnetic pump. The heating power introduced by the electrons is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are between 1 m/s and 5 m/s in the radiator section. From the thermal and mechanical point of view, molybdenum turned out to be the most suited target wall material in the region where the electrons impinge on the neutron radiator. To reduce the radiation background at the measurement position, the neutrons are decoupled from the radiator at an angle of about 90° with respect to the impinging electrons. Particle transport calculations using the Monte Carlo codes MCNP and FLUKA predict a neutron source strength in the range of 7.9 × 10 12 n / s to 2.7 × 10 13 n / s for electron energies between E e - = 20 and 40 MeV. At the measuring place 3.9 m away from the radiator, a neutron flux of about 1.5 × 10 7 n / ( cm 2 s ) will be obtained. The short beam pulses allow for a neutron energy resolution of better than 1% for neutron energies between E n = 50 keV and 5 MeV. The usable energies range up to about 10 MeV.

The 235U(n, f) reaction cross section was measured relative to neutron-proton elastic scattering for the first time in the energy region from 10 MeV to 440 MeV at the CERN n_TOF facility, extending the upper limit of the only previous measurement in the literature by more than 200 MeV. For neutron energies below 200 MeV, our results agree within one standard deviation with data in literature. Above 200 MeV, the comparison of model calculations to our data indicates the need to introduce a transient time in neutron-induced fission to allow the simultaneous description of (n, f) and (p, f) reactions.