MCNP模拟钴-60辐照装置空间剂量场

为模拟辐照室中辐照工位外的周围空间剂量场分布，采用蒙特卡罗粒子输运程序MCNP建立钴-60辐照装置模型。以单板源架中心点为坐标原点的笛卡尔坐标系，考虑钴-60源的γ射线非自吸收和自吸收两种情况，研究坐标轴方向上每隔10 cm间距的空气平面的剂量率和坐标轴上剂量率的变化规律。结果表明，辐照室中辐照产品占满辐照工位的情况下，周围空间剂量场空气面剂量率整体较小；单板源架中心坐标轴上的剂量率变化规律更符合二项式拟合函数。在钴-60源γ射线自吸收情况下，单板源架端面坐标轴附近的空气面剂量率明显偏小，且随着空气面远离单板源架，空气面上的高剂量率区域向两侧移动；在钴-60源γ射线非自吸收情况下，单板源架端面处的空气面高剂量区域始终位于坐标轴附近。MCNP理论模拟计算分析对于利用钴-60辐照装置辐照工位外的周围空间剂量场具有重要的实际指导意义。

MCNP Simulating the Apatial Dose Field of Cobalt-60 Irradiation Facility

The Monte Carlo particle transport code program MCNP is used to establish a cobalt-60 irradiation device model and simulate the peripheral spatial dose field distribution outside the irradiation station in the irradiation room. The Cartesian coordinate system is established with the center point of the single-rack source frame as the coordinate origin. Considering the γ-rays non-self-absorption and the γ-rays self-absorption of cobalt-60 source, the dose rate distribution of the air surface at intervals of 10 cm along the coordinate axis and the variation law of dose rate on the coordinate axis are studied. The results show that the dose rate of the peripheral spatial dose field is relatively small, when the irradiation products of the irradiation room occupy all the irradiation stations. The variation law of dose rate on the coordinate axis of the single-rack source frame is more consistent with binomial fitting function. In the case of γ-rays self-absorption of cobalt-60 source, the dose rate near the coordinate axis of the single-rack source frame is obviously low, and the high-dose-rate region of the air surface moves to both sides as air surface moves away from the single-rack source frame. In the case of γ-rays non-self-absorption of cobalt-60 source, the high-dose-rate region of the air surface at the end face of the single-rack source frame is always located near the coordinate axis. The theoretical simulation calculation and analysis of MCNP has important practical guiding significance for the peripheral spatial dose field outside the irradiation station in the irradiation room of the cobalt-60 irradiation facility.