Abstract: Presents a methods for calculation of the thickness of a concrete roof for shielding the angularity distributed X-ray radiation produced by a L-6000HRO 15MeV X-ray Linear Accelerator. The required roof thickness was found to be 31cm in order to ensure the dose equivalent rate to be 0.0025mSv. h^-1 at an observation point 20 m away from the machine. This radiation comes mainly from skyshine. The thickness of that concrete roof was further optimized and found to be 50 cm. The dosimetric measurements made after the accelerator building had constructed showed that the shielding design was safe and econonic, and the skyshine radiation had been decreased to a level as low as reasonably achievable.

Key words: X-ray, linear accelerator, calculation of roof thickness, optimization, skyshine, concrete

摘要： 提出了具有角分布辐射源的屋顶厚度计算方法，计算了L-6000HRO15MeVX射线直线加速器在离源d_s=20m处，由天空回散照射产生的剂量当量率降低到2.5×10^-3mSv·h^-1时，所需的混凝土屋顶厚度为31cm, 最优化的屋顶厚度为50cm，竣工后检测，周围环境剂量当量率为本底水平，达到了可以合理达到的尽量低的水平。用本方法计算的屋顶屏蔽厚度，既有足够的安全水平，又能节省投资。

关键词: X射线, 直线加速器, 屋顶厚度计算, 最优化, 天空回散照射, 混凝土