Design of bremsstrahlung target of 4 MeV flash X-ray machine
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摘要: 对4 MeV闪光X光机的轫致辐射靶参数进行了设计和模拟计算。利用蒙特卡罗程序，计算得到当轫致辐射靶的有效钽靶材厚度约为0.6 mm时，靶正前方1 m处产生的单脉冲X光的照射量值最大，可以达到约2.86×10－3 C/kg，满足4 MeV闪光X光机对其单脉冲X光的设计要求。对不同能量下的单脉冲电子束加载在轫致辐射靶上的能量沉积密度进行了计算和比较，分析研究了不同结构下的靶破坏，结果表明：轫致辐射靶采用叠靶结构的钽靶能够满足4 MeV闪光机的实验需求。Abstract: Bremsstrahlung converter target is one of the key factors for flash X-ray machine. The bremsstrahlung radiation process in which the electron beam impinges on the target is simulated utilizing the Monte Carlo method, by which the influence of the effective target thickness on the exposure is analyzed, the optimal target thickness and the exposure are also obtained for the 4 MeV flash X-ray machine. The damages of target impacted by the electron beam are compared and discussed for various electron energy deposit density from different sources, such as 12 MeV LIA, Dragon accelerators and 4 MeV flash X-ray machine. The results show that the tantalum distributed target may be the satisfactory solution for the bremsstrahlung target of 4 MeV flash X-ray machine.
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Key words:
- bremsstrahlung /
- Monte Carlo /
- exposure /
- energy deposit /
- distributed target
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图 2 归一化X光照射量随钽靶厚度的变化曲线
Figure 2. Curve of normalized X ray exposure versus tantalum thickness
图 3 0.6 mm钽靶产生的归一化光通量随辐射角分布
Figure 3. Curve of normalized photon flux versus radiation angle for 0.6 mm tantalum target
图 6 不同脉冲作用下的神龙二号加速器钽叠靶的破坏
Figure 6. Damage of the tantalum distributed target impinged by different electron beams from Dragon-Ⅱ accelerator
图 5 神龙一号加速器钽叠靶破坏
Figure 5. Damage of tantalum distributed target for Dragon-Ⅰaccelerator
表 1 照射量转换因子的能量依赖关系
Table 1. Exposure conversion factor change with photon energy
$h\nu $/MeV $\varepsilon $ /（J·m－2·R－1） 0.01 0.019 0.02 0.171 0.05 2.151 0.1 3.847 0.2 3.294 0.5 2.940 1 3.140 2 3.731 3 4.258 4 4.668 5 4.960 6 5.291 8 5.706 10 5.979 15 6.419 20 6.364 
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表 2 单脉冲电子束作用下靶正前方1 m处X光照射量比较
Table 2. Comparison of X ray exposure at 1 m just in front of the target impacted by the single pulse electron beam
methods W/MeV I/kA $\tau $/ns X/(C·kg－1) Martin formula 4 2.5 60 2.07×10－3 MCNP simulation 4 2.5 60 2.86×10－3
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表 3 单脉冲电子束作用下不同轫致辐射靶的破坏比较
Table 3. Comparison of damage for different bremsstrahlung targets impacted by single pulse electron beam
W/MeV I/kA $\tau $/ns X-ray spot/mm D/（J·mm－2） target structure target destroyed 12 MeV LIA 12 2.5 80 3.2 298.6 slab melting ablation/perforation distributed no change Dragon-Ⅰ 20 2.0 60 1.5 1358.8 distributed perforation Dragon-Ⅱ 20 2.0 60 2 764.3 distributed perforation 4 MeV X-ray machine 4 2.0~2.5 60 2 152.9～191.1 distributed no transformation (estimated)
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