Simulation and source design of large area uniform bremsstrahlung field
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摘要: 基于蒙特卡罗方法建立了单环及双环平行电子束轰击钽靶模型，以此模拟环形二极管产生轫致辐射场的过程。模型选用电子束能量为1.5 MeV，钽金属靶厚度为200 μm，并采用探测器计数方法对单环电子束在靶后10 cm产生的轫致辐射场剂量进行模拟研究。对于单环二极管结构，环内径是影响靶后轫致辐射场均匀性的主要因素，内径越大，中心剂量均匀性越差。相比环内径，环宽则主要影响辐射场的剂量大小，对于均匀性的影响较小。当单环内径为19 cm、外径为20 cm时，能得到最大面积为
2 290.221 cm2的均匀辐射场。双环二极管结构对比单环结构能得到更大面积的均匀辐射场。但外环环径的变化会导致辐射场剂量分布出现多级峰值，同时对辐射场各个区域的均匀性造成影响。模拟结果表明，通过在上述单环结构外侧添加内径为43.5 cm、外径为44.167 cm的同心外环，可将满足均匀度要求的辐射场面积增大至7 238.229 cm2。Abstract: Bremsstrahlung diode is an important device for obtaining large area uniform bremsstrahlung field in laboratory. In this paper, based on Monte Carlo method, a model of single and double ring parallel electron beam bombarding tantalum target is established to simulate the process of bremsstrahlung field generated by ring diode. The electron beam energy is 1.5 MeV, the tantalum target thickness is 200 μm, and the dose of bremsstrahlung field generated by a single ring electron beam 10 cm behind the target is simulated by detector counting method. For single-ring diode structure, the inner diameter of the ring is the main factor affecting the bremsstrahlung field uniformity behind the target, and the larger the inner diameter, the worse the central dose uniformity. Compared with the inner diameter of the ring, the ring width mainly affects the dose of the radiation field, but has little influence on the uniformity. When the inner diameter of a single ring is 19 cm and the outer diameter is 20 cm, a uniform radiation field with a maximum area of2290.221 cm2 can be obtained. When the inner diameter of a single ring is 19 cm and the outer diameter is 20 cm, a uniform radiation field with a maximum area of2290.221 cm2 can be obtained. The double-loop diode structure can obtain a larger area of uniform radiation field than the single-loop structure. However, the variation of the outer ring diameter leads to multi-level peaks in the dose distribution of the radiation field, which also affects the homogeneity of each region of the radiation field. The simulation results show that by adding a concentric outer ring with an inner diameter of 43.5 cm and an outer diameter of 44.167 cm to the outside of the single ring structure, the radiation field area meeting the uniformity requirement can be increased to7238.229 cm2.-
Key words:
- X-ray /
- ring diode /
- bremsstrahlung /
- Monte Carlo method /
- homogeneity
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图 2 靶后10cm轫致辐射场分布
Figure 2. Dose distribution of the 10 cm bremsstrahlung radiation field after the target
图 3 不同内径下的剂量峰值以及中心均匀度大小
Figure 3. Dose peak and center uniformity at different inner diameters
图 4 最大均匀辐射场面积与内径的关系
Figure 4. Relationship between the area of the maximum uniform radiation field and the inner diameter
图 7 靶后10 cm轫致辐射场分布
Figure 7. Dose distribution of the 10 cm bremsstrahlung radiation field after the target
图 8 不同外环内径下的辐射场参数
Figure 8. Radiation field parameters under different inner diameters of outer rings
图 9 靶后10 cm轫致辐射场分布（r3=43.5cm）
Figure 9. Dose distribution of the 10 cm bremsstrahlung radiation field after the target (r3=43.5cm)
表 1 不同内径对应次级凹陷处的均匀度大小
Table 1. Different inner diameters correspond to the uniformity of the secondary depression
r3/cm dose uniformity r3/cm dose uniformity 42 0.5454 43 0.5168 43.5 0.5019 44 0.4892 
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