Measurement of the beam spot characteristics at the CSNS Back-n white neutron source

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) plays a significant role in nuclear data measurement, irradiation experiments, and neutron resonance imaging. As one of the key characteristics of the neutron beam, the measurement and detailed analysis of the beam spot are essential. In this study, systematic measurements of multiple beam spots were conducted at different neutron time-of-flight distances in the two experimental stations of Back-n, utilizing a ZnS( 6 Li) neutron-photon conversion screen coupled with a high-time-resolution iCMOS camera. The study focuses on analyzing the profiles, dimensions, and beam halo characteristics of these commonly used beam modes. These characteristics are fundamental for users conducting various physics experiments, such as nuclear data measurement and neutron imaging, at the back-n white neutron source.