Study on collimator design for Neutron Science Facility of RAON accelerator complex

摘要

The RAON heavy ion accelerator complex is under development for the Rare Isotope Science Project (RISP) in Korea. The Neutron Science Facility (NSF) in RAON will perform Time of Flight (TOF) experiments in order to measure cross section data of fast neutrons. Fast neutrons are produced from a graphite target irradiated by a 53 MeV of deuteron beam. Consequently, a collimator that provides a highly focused neutron beam to the TOF system while reducing the background in the TOF hall should be considered. The collimator was designed by optimizing several design parameters such as the beam channel diameter, beam channel shape, and collimator type. Additionally, for the safety of workers during the operation of the NSF, an activation analysis was carried out. As a result, the final design of the collimator for the RAON NSF has a 4 m length, and channel of 0.5/2 cm in the entry/exit radius in a conical-opened shape. Materials were arranged in a ring type by setting 1 cm of the iron inside, and 20 cm of 5% borated polyethylene outside. With the final design of the collimator, a 95.7% background reduction was achieved while maintaining the original neutron beam intensity. The shut-down dose rate inside the TOF room satisfies the exposure limit.