A multi-cell fission chamber for fission cross-section measurements at the Back-n white neutron beam of CSNS

A multi-cell fast ionization chamber (FIC) has been designed and built as an initial detector for fission cross section measurement on the Back-n neutron beam at the China Spallation Neutron Source (CSNS). The current FIC has been carefully optimized to match the features of the neutron beam with capability of mounting up to 10 cells. The basic principle and characters of this detector and the front-end electronics are presented, together with the performance test during the first measurement campaign on the Back-n beam line. Some signal processing methods have been applied to deal with the poor γ-flash signals induced by the low intensity neutron beam. The current FIC shows good performances in high timing precision and clear background discrimination.