A compact multi-plate fission chamber for the simultaneous measurement of ²³³U capture and fission cross-sections

E-ISSN： 2100-014x|146|issue|03027-03027

ISSN： 2100-014x

Source： EPJ Web of Conference, Vol.146, Iss.issue, 2017-09, pp. : 03027-03027

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Abstract

²³³U plays the essential role of fissile nucleus in the Th-U fuel cycle. A particularity of ²³³U is its small neutron capture cross-section which is about one order of magnitude lower than the fission cross-section on average. Therefore, the accuracy in the measurement of the ²³³U capture cross-section essentially relies on efficient capture-fission discrimination thus a combined setup of fission and γ-detectors is needed. At CERN n_TOF the Total Absorption Calorimeter (TAC) coupled with compact fission detectors is used. Previously used MicroMegas (MGAS) detectors showed significant γ-background issues above 100 eV coming from the copper mesh. A new measurement campaign of the ²³³U capture cross-section and alpha ratio is planned at the CERN n_TOF facility. For this measurement, a novel cylindrical multi ionization cell chamber was developed in order to provide a compact solution for 14 active targets read out by 8 anodes. Due to the high specific activity of ²³³U fast timing properties are required and achieved with the use of customized electronics and the very fast ionizing gas CF₄ together with a high electric field strength. This paper describes the new fission chamber and the results of the first tests with neutrons at GELINA proving that it is suitable for the ²³³U measurement.