Development of Ionisation Chambers for the Simultaneous Measurement of the Neutron-induced Capture and Fission Cross Section of 233U

Abstract

A new simultaneous measurement of σ(n,f) and σ(n, γ) will be performed at the neutron time-of-flight facility GELINA in Geel (Belgium). The fission events will be detected by a multi-plate high-efficiency ionisation chamber (IC). An efficient array of C6D6 scintillators will be used for the detection of gamma-rays. The disentanglement between fission and capture gamma-rays can be achieved by using anticoincidence events between the IC and the C6D6 detectors. Given the difference in the fission and capture cross sections, the assignment of a gamma-ray to one or the other reaction type has to be very efficient and reliable. The IC efficiency is not 100 % and a correction has to be applied to take into account the undetected fission events. To keep this correction factor low and reliable, the efficiency parameter of the IC should be high and known with a high degree of accuracy. The IC efficiency towards fission can be defined as a ratio between the number of detected neutrons in coincidence or not with fission fragments. It is therefore a value directly extractable from the experimental data. Results from test experiments of the IC will be presented and discussed, along with IC MCNPX simulations.