摘要:
提出了一种基于射频直线加速器的多脉冲X光照相系统,有望用于材料动态性能诊断等流体物理动力学研究.基于射频加速器的特点,该套照相系统能够产生时间跨度10 μs以上、数个脉冲间隔可调、脉宽为几十至一百ns的脉冲电子束,产生电子束束斑半高宽尺寸小于1 mm.通过蒙特卡罗模拟程序Geant4,分析计算了特定的几何布局以及不同厚度及电子束束斑条件下,电子束打靶后在靶中的能量沉积,靶中的电子束散射对X光焦斑的影响,以及1 m处的照射量,探讨了这套X光照相系统的应用可行性.结果表明,在30 MeV,400 nC电子束轰击厚度为1 mm的靶条件下,1 m处照射量约为9.1R,靶厚在1～2 mm范围内并未引起X光焦斑的明显增大.较小横向尺寸的电子束会引起靶体局部升温严重,将会制约脉冲数量;采用旋转靶能够提升脉冲数量,通过分析二维旋转靶的应力,分析了靶材升温以及钽/钽合金屈服强度对脉冲间隔的限制作用.
Abstract:
A multi-pulse X-ray radiography system,based on an RF linear accelerator,was suggested to be employed in diagnosis for hydrodynamic test.The system can provide several interval-adjustable electron pulses,with pulse widths of tens to a hundred nanoseconds and beam transverse size (FWHM) less than 1 mm,within a duration of 10 μs.We used Monte Carlo codes,Geant4,to simulate bremsstrahlung characteristics,such as exposure dose,energy deposit in target and increment of X-ray spot size by electron scatter,of 30 MeV electron beams bombarding tantalum target with various thickness in a certain radiography layout.Simulation results show that the exposure dose at 1 m away from the target right ahead was about 9.1 R and the X-ray spot sizes were not increased obviously with the thickness increment.The pulse number was limited by temperature rise in target,which was increased intensely with a very tiny beam transverse size.The rotating target could be employed to break the limitation of pulse number,but the pulse interval was limited by decrement of yield strength with the rise of target temperature.
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