Preliminary results on the $^{233}$U $\alpha$-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,$\gamma$) cross section relies on a method to accurately distinguish between capture and fission $\gamma$-rays. A measurement of the $^{233}$U $\alpha$-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 $\gamma$-rays. The experimental setup is described and essential parts of the analysis are discussed. Finally, a preliminary $^{233}$U $\alpha$-ratio is presented.