Preliminary results on the 233U α-ratio measurement at n_TOF

233 U is the fissile nuclei in the Th-U fuel cycle with a particularily small neutron capture cross setion which is on average about one order of magnitude lower than its fission cross section. Hence, the measurement of the 233 U(n, γ ) cross section relies on a method to accurately distinguish between capture and fission γ -rays. A measurement of the 233 U α -ratio has been performed at the n_TOF facility at CERN using a so-called fission tagging setup, coupling n_TOF 's Total Absorption Calorimeter with a novel fission chamber to tag the fission γ -rays. The experimental setup is described and essential parts of the analysis are discussed. Finally, a preliminary 233 U α -ratio is presented.