Development of an experimental set-up for the measurement of neutron-induced fission and capture cross sections of highly radioactive fissile nuclei

¹ Centre d'Etudes Nucléaires Bordeaux Gradignan, CNRS/IN2P3, Univ. Bordeaux 1, Chemin du Solarium, F-33175 GRADIGNAN, France
² EC-JRC, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, B-2440 Geel, Belgium
³ CEA/Saclay - DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette, France
⁴ Laboratoire de Physique Subatomique et de Cosmologie, CNRS/IN2P3, Univ. Joseph Fourier, INPG, 53 avenue des Martyrs, F - 38026 Grenoble Cedex, France

^a Corresponding author: mathieu@cenbg.in2p3.fr

Published online: 1 April 2014

Abstract

The measurement of neutron-capture cross sections of many actinides is complicated by the difficulty in separating capture γ-rays from the large fission-fragment prompt γ-ray background. For example, current estimates of the capture cross section of ²³³U show large discrepancies, with differences of more than 20%. To improve the accuracy of data, a new experimental set-up for the simultaneous measurement of the neutron-induced capture and fission cross sections was designed, assembled and optimized. The measurements will be performed at the GEel LINear Accelerator (GELINA) neutron time-of-flight facility in Belgium, where neutron cross sections can be measured over a wide energy range with high energy resolution. The fission detector consists of a dedicated multi-plate high-efficiency ionization chamber (IC). The γ-rays produced in capture reaction are detected by an array of C₆D₆ scintillators. Fission γ–rays are distinguished from capture γ–rays by the anticoincidence signals from the IC and the C₆D₆ detectors. For the undetected fission events a correction has to be applied based on the efficiency of the IC that should be high and known with a high accuracy. The performance of the IC during dedicated test experiments is presented, focusing on the determination of the detection efficiency.