Studies of back-streaming white neutrons at CSNS

Back-streaming neutrons through the incoming proton channel at the spallation target station of China Spallation Neutron Source (CSNS) are harmful to the proton beam line and should be dealt with carefully. On the other hand, those back-streaming neutrons may be useful for other applications. This paper presents preliminary studies on the characteristics of the neutrons, which have a very wide energy spectrum (white neutrons) and are very suitable for nuclear data measurements. The corresponding yields and time structures of the neutrons in the energy range of 1 eV to 1 MeV from a tungsten target for a proton beam of 1.6 GeV in energy and 63 μA in average current have been simulated. From the simulation results, one can obtain an uncollimated neutron flux of around 2.0×105 n/cm2/pulse within the given energy range at 80 m away from the target, which accounts for about 53% of the total neutrons. The time resolution of 0.3–0.9%, which is important for the time-of-flight method, is obtained for both the parasite operation mode with two proton bunches and the dedicated operation mode with a single proton bunch.