GRAPhEME: a setup to measure (n, xnγ) reaction cross sections

Most of nuclear reactor developments are using evaluated data base for numerical simulations. However, the considered databases present still large uncertainties and disagreements. To improve their level of precision, new measurements are needed, in particular for (n, xn) reactions, which are of great importance as they modify the neutron spectrum, the neutron population, and produce radioactive species. In 2003, the IPHC group started an experimental program to measure (n, xn gamma) reaction cross sections using prompt gamma spectroscopy and neutron energy determination by time of flight. Measurements of (n, xn gamma) cross section have been performed for U-235,U-238, Th-232, (nat,182,183,184,186) W, Zr-nat. The experimental setup, consisting of HPGe detectors and a fission chamber, is installed at the neutron beam at GELINA (Institute for Reference Materials and Measurements (IRMM), Geel, Belgium). It has recently been upgraded with the addition of a highly segmented 36 pixels planar HPGe detector. The setup is equipped with a high rate digital acquisition system. The analysis of the segmented detector data requires a specific procedure to account for cross signals between pixels. An overall attention is paid to the precision of the measurement. The setup characteristic and the analysis procedure will be presented along with the acquisition and analysis challenges. Examples of results and their impact on models will be discussed. Finally, the perspectives on complimentary experiments will be presented.