Ten years of use of powerful spectrometers at the JRC-Geel site linear accelerator
In collaboration with users of the JRC-Geel site linear accelerator (GELINA), JRC scientists provided a summary of the experiments and findings from the use of two specific detectors at GELINA through studying gamma-emission from nuclei excited by neutron scattering.
The so-called inelastic neutron scattering process is perhaps amongst the poorest characterised reactions with an important impact on criticality estimates of power reactors. This fact significantly limits the possibility of achieving low uncertainties in criticality assessments.
The JRC-Institute for Reference Materials and Measurements (IRMM), located in Geel, Belgium, hosts a powerful linear accelerator used by scientists, not only from the JRC-IRMM, but also from many nuclear research organisations worldwide. Two powerful spectrometers, GAINS (Gamma Array for Inelastic Neutron Scattering) and GRAPHEME (Germanium Array for Actinides Precise Measurements, an instrument from the Hubert Curien Multidisciplinary Institute (IPHC) Strasbourg) were developed since ten years ago to improve the knowledge of this process. The overall aim was to achieve accurate measurements with high selectivity and resolution by a combination of the best available gamma-detectors and the neutron time-of-flight technique. The two arrays (now 12 and 5 detectors, respectively) have taken full advantage of technological developments in data-acquisition and detector technology.
Combined with large germanium detectors, GAINS focuses on high neutron energy resolution for non-radioactive materials such as iron, chromium, magnesium while GRAPhEME works with thin actinide targets such as Th-232, U-235, U-238. The newly available data challenge theoreticians and evaluators with a volume of data for which modelling is qualitatively reasonable but not in quantitative agreement with the measurements. The latter is needed for the consistent inclusion of the data in high quality evaluated nuclear data files that may be used in taxing applications such as criticality estimates.
The experts concluded by expressing the need to maintain and develop strong collaborations with both evaluators and theoreticians in the field of nuclear reaction modelling. Such collaborations will enable the provision of high-quality experimental data of interest.