Analysis of the shielding effect of protective door of an 18 MV linear accelerator debugging room and its influencing factors
Objective To study the shielding effect of the protective door of a maze-free debugging room for an 18 MV medical linear accelerator and its influencing factors,and to provide guidance for protection of debugging personal against radioactive occupational disease hazards.Methods The investigation focused on the protective door of a newly construc-ted maze-free debugging room for an 18 MV medical linear accelerator.The protective door was made of the following shielding materials from inside to outside:2.5 cm steel plate+20 cm lead+41 cm polyethylene containing 5%boron+6 cm lead+2.5 cm steel plate.The right side of the protective door was provided with a groove(commonly known as"door pock-et")lap.With different lap widths,irradiation directions,and installation positions of the accelerator base,FLUKE451P and WENDI Ⅱ neutron detectors were used to measure the ambient dose equivalent rate of the points of interest outside the pro-tective door.The shielding effect and influencing factors were analyzed.Results When the lap width at both sides of the protective door was 300 mm,the ambient dose equivalent rates outside the protective door were(1.37±0.05)μSv/h on the side with"door pocket"and(4.71±0.11)and(4.19±0.11)μSv/h on the side without"door pocket".When the primary beam of the accelerator was directed towards the east,the ambient dose equivalent rates at the points of interest outside the protective door were higher than those of the corresponding points of interest when the primary beam was directed towards other directions.When the accelerator base was located on the south side of the machine room,the ambient dose equivalent rates of the points of interest outside the protective door under the same irradiation conditions were lower than those when the accelerator base was located on the north side of the machine room.Conclusion The study of an 18 MV accelerator and its maze-free debugging room showed that the radiation of photons and neutrons should be taken into consideration when designing the protective door at the entrance.The protective door with shiplaps on both sides of the wall has improved shielding effect outside the door.
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