A Preliminary Study for Safety Shutter design to Protect Streaming of Residual Radiation Passing through Beamline in Pre-Separator Room of ISOL

RAON is a heavy ion accelerator under construction by the Institute for Basic Science (IBS) in Korea. As one part of the RAON accelerator, ISOL is a facility to generate and separate rare isotopes for various experiments. In ISOL facility, isotopes generated from the reaction between 70 MeV proton beam and UC₂ target are transferred to pre-separator room. Almost all isotopes accumulated in slit of pre-separator except specific isobars, which are set for experiments. Residual radiations are generated from accumulated isotopes because these isotopes are unstable. Streaming of residual radiation by the beamline is weak point for radiation shielding design. In this study, safety shutter was designed. Residual radiation generated from accumulated isotopes at slit of pre-separator was estimated using following conditions: (1) the isotopes generated by proton-target reactions are accumulated at slit with 10 % accumulation rate; (2) it was assumed that the radioactive isotopes are uniformly distributed in the cylindrical slit which have 1 cm height and 15 diameter. To design optimized safety shutter, following steps were performed: (1) thickness and diameter of the bulk shield material were evaluated to optimize safety shutter material; (2) additional shielding structure was proposed using dose contribution of each additional shielding wall